INTRODUCTION

The U.S. Geological Survey (USGS) is assisting in the compilation of a series of digital maps of Quaternary faults and folds in Western Hemisphere countries as part of the International Lithosphere Program's (ILP) Task Group II-2 project entitled “World Map of Major Active Faults.” The maps from this project show the locations, ages, and activity rates of major earthquake-related features such as faults and fault-related folds. They are accompanied by databases that describe these features and document current information on their activity in the Quaternary. To date, the project has published fault and fold maps for Costa Rica (Montero and others, 1998), Panama (Cowan and others, 1998), Venezuela (Audemard and others, 2000), Bolovia and Chile (Lavenu, and others, 2000), Argentina (Costa and others, 2000), Colombia (Paris and others, 2000), the Managua region of Nicaragua (Cowan and others, 2000) and Brazil (Saadi and others, 2002). The project is a key part of the Global Seismic Hazards Assessment Program (ILP Project II-0) for the International Decade for Natural Hazard Disaster Reduction.

The project is sponsored by the International Lithosphere Program and funded by the USGS’s National Earthquake Hazards Reduction Program. The primary elements of the project are general supervision and interpretation of geologic/tectonic information (Michael N. Machette, Project Chief), data compilation and entry for fault catalog (all personnel), database design and management (Kathleen M. Haller), and digitization and editing of fault and fold traces (Richard L. Dart) in †ARCINFO. For the compilation of data, we engaged experts in Quaternary faulting, neotectonics, paleoseismology, and seismology. These experts (i.e., Eguez, Alvarado, and Yepes) are the primary authors of this report and questions about individual fault descriptions should be directed to them. Questions about the project, its status, and the GIS map should be directed to the USGS authors.

Prior to initiating this project, no modern or digital map of active or Quaternary faults existed for Ecuador or any other country within South America, even though understanding the extent and character of active and older Quaternary faults are critical elements of seismic hazards analysis. Creation of this map and the accompanying database will help extend the relatively short record of instrumental and felt seismicity in Ecuador by creating a paleoseismic record of surface deformation associated with large (M>6.5) earthquakes. This database can be used to identify both well and poorly studied faults, and can be used as a guide for improving the geologic input to seismic hazard assessments.

Although fault data are available for most of the country, the degree of completeness varies greatly and often is a function of the degree of remoteness and vegetation cover, such as east of the Ecuadorian Andes. A few faults have been the subject of recent investigations involving modern paleoseismic techniques, but most have not. Some regions and faults have been studied in moderate detail, usually in association with concerns about hazards to urban areas or the safety of critical facilities such as lifelines, oil-and-gas pipelines, or power-generating facilities. Thus, considerable effort was required from the primary authors in order to compile information from a wide variety of sources and insure that the national product is up to date and provides fairly uniform coverage for the entire country. Nevertheless, the general state of knowledge for faulting in Ecuador is probably best described as being of a reconnaissance nature. Little is known in a collective sense about the overall rates of fault activity and fault chronology—information that is difficult to acquire, but critical to seismic-hazard assessments. Hopefully, additional paleoseismic studies will help augment this map and database.

STRATEGY AND PURPOSE

For the map of Ecuador, we relied on known, productive experts with strong local or regional knowledge of Ecuador who were willing to participate in this international project. The main compilers were Arturo Eguez and Hugo Yepes, with help from Alexandra Alvarado. Given the limited time Task Group II-2 was given to produce the map, the project was restricted to compilation of just those elements needed for ILP's Global Seismic Hazards Assessment Program (see database). We anticipate that the project will point out the shortcomings of past and current research on Quaternary faulting in Ecuador in terms of quantity, quality, scope, and regional coverage and should help promote new efforts to collect paleoseismological data in previously neglected or known critical areas.

In many cases, seismicity is used to define potentially active faults, especially along active plate margins. However, recent faulting events in the Western Hemisphere have shown that much of the faulting away from active plate margins occurs along faults with no significant level of seismicity and that only a fraction of active faults are characterized by ongoing seismicity. Thus, the information on Quaternary faulting included within this database should help extend the modern (past several hundred years) record of seismicity into prehistoric time, and allow better assessments of active and potentially active faults in Ecuador and other Western Hemisphere countries.

TECTONIC SETTING

Ecuador comprises three main morphostructural regions: the coastal plain, the Andean range consisting of the Cordillera Occidental (western) and Cordillera Real or Oriental (eastern), and the upper Amazon basin (see index map on map). They represent the fore-arc, volcanic arc and back-arc zones (respectively), all related to the active subduction of the oceanic Nazca Plate beneath the continental South America Plate. The general geologic and tectonic framework is a product of a complex geologic history involving several accretionary processes that have produced spatial and temporal overlay of different geotectonic terranes (Eguez and Aspen, 1993; Litherland and others, 1994).

The Andean uplift and the present distribution of terrains are related to active subduction, but they probably started being formed in Mesozoic time and perhaps much earlier. In fact, the above morph-structural regions appear to be controlled by conspicuous NNE-SSW trending fault systems acting partially along regional suture zones.

The Eastern region of Ecuador consists of the Upper Amazon basin formed by dominant sedimentary series floored by the Guyana craton (not exposed). The Subandean zone (Napo and Cutucu foothills) appears at the margin of the Andean range: this zone includes folded Mesozoic sedimentary rocks and is bounded by thrust systems on the east that show significant Neogene motion. The Andean Range is formed by the Cordilleras Real and Occidental (western), which are separated by the Interandean Valley. The Cordillera Real includes metamorphic sequences and Triassic granitoids that are intruded into Paleozoic(?) pelagic sediments and Jurassic volcanic and sedimentary suites assigned to oceanic and continental arc environments (Litherland and others, 1994). The western structural margin of the Real Cordillera outlines the Peltetec suture, which seems to coincide partially with the southern extension of the Romeral system in Colombia. The Cordillera Occidental and the Coastal plain represent the extension of the same morphostructural regions as in Colombia. They comprise allochtonous, unmetamorphosed oceanic rocks as young as Eocene age, confirming that the last accretionary event occurred before the Pacific Plate was reorganization at 26 Ma (Hey, 1977). The eastern structural limit of this oceanic terrain follows the Calacali-Pujili suture zone extended along the western border of the Interandean Valley. It seems to correspond to the southern extension of the Cauca-Patia fault zone reported in Colombia and which is part of the Romeral fault system.

According to Pennington (1981), Ecuador represents a portion of the Northern Andes where the Nazca Plate (slab) dips at 35°E. Nevertheless, a more detailed analysis of the different seismicity profiles shows a more complex behavior of the slab (Gutscher and others, 1999). Thus, Gutscher and others (1999) concluded that Ecuadorian subduction system appears highly controlled by the subduction of the Carnegie Ridge and by the lithospheric tears within the Nazca Plate. The most recent devastating earthquake in Ecuador occured on August 5, 1949. It is not known if this earthquake caused surface rupturing, but it caused nearly 6,000 deaths in north-central Ecuador. The epicentral location is 1.2°S and 78.5°W, near Ambato about 115 km south of Quito. The most recent large subduction zone interface earthquake (Mw 8.8) to strike Ecuador occurred on January 31, 1906 and killed 1,000 people. The epicenter of this subduction zone earthquake was located at 1°N and 81.5°W, about 150 km offshore of an area of northern Ecuador that was not densely populated at the time (nearly 100 years ago).

MAJOR STRUCTURAL ELEMENTS

Preliminary studies suggest that mega faults control the boundaries of the Northern Andes. Campbell (1974) defined the Dolores-Guayaquil Megashear along the Andean ranges, and Pennington (1981) proposed the Eastern Andean Frontal fault zone as the limit of the North Andean block along the Subandean region.

In fact, the North Andean block appears limited by an active NNE-trending dextral strike-slip fault system. These observations suggest that the dextral motion along the NNE regional faults changes to compressional motion where the faults have a N-S trend; all accommodating E-W compressional stress produced by the convergence of the South American and Nazca plates (see tectonic inset map on plate). Field observations show that the main fault systems are oblique to the Ecuadorian Andes, starting at the Gulf of Guayaquil (Pallatanga fault, EC-50) and cutting across the ranges toward the eastern border of the Cordillera Real (Chingual fault, EC-54) in northern Ecuador (Soulas and others, 1991). These two main NE-SW faults show significant strike-slip morphology and kinematic features and they are probably responsible for the main historic earthquakes in Ecuador.

Between these faults, the slip motion is accommodated by minor NE-SW oblique faults and by N-S fault zones along the Interandean Valley, where folds, flexures, and related reverse faults (including the Quito fault, EC-31) have been identified. Also, a transpressional NNE-SSW fault system along the Subandean zone partially accommodates E-W compression.

The tectonic regime of the coastal region appears highly controlled by subduction of the Carnegie Ridge and by the oblique convergence of the Nazca Plate. Thus, normal and reverse faults bound small blocks in front of the Carnegie Ridge and a main transpressional fault system limits the northern coastal ranges, thus defining active fore-arc basin filled by alluvial fans on the piedmont of the Cordillera Occidental.

PREPARATION OF MAP AND DATABASE

This compilation shows evidence for activity on Quaternary faults and folds in Ecuador and offshore regions in the Pacific Ocean. The data were compiled during 1994-97 from the available published literature (through 1998), recent geological investigations, and from interpretation of aerial photographs by the senior authors. Arturo Eguez mainly compiled the surface traces of the Quaternary faults and folds. Offshore traces are based primarily on marine geophysical studies and bathymetric maps; these traces are inherently less well defined and located, and should be considered approximate. Michael Machette edited most of the text and map data and provided guidance for the project under the International Lithosphere Program's Task Group II-2 "Major Active Faults and Folds of the World," for which he is the Co-chairman (Western Hemisphere).

Richard Dart used GIS (Geographic Information System) technology to produce the fault and fold maps. The traces of Quaternary faults and fold were digitized, attributed for age, sense of slip, and line type (continuous, discontinuous, and concealed or inferred), and reprocessed using a Mercator projection. The maps were prepared with ARC/INFO version 7.1.2 running under Solaris version 2.5.1 on a Unix workstation. Data for the fault length and average strike were generated from the ARC/INFO files.

The base-map information was taken from the Digital Chart of the World, which was created for use with ARC/INFO (copyright 1993 by the Environmental Systems Research Institute, Inc.). The Digital Chart of the World was compiled at a scale of 1:1,000,000, but is reasonably detailed at the printed scale of the map (1:750,000). It was originally developed for the United States Defense Mapping Agency (DMA) and is primarily derived from the DMA Operational Navigation Chart (ONC) Series.

Map

The map of Quaternary faults and folds of Ecuador was compiled on an overlay using the Ecuador geologic map as a base; the faults were digitized at a scale of 1:1,250,000. The GIS data is scale independent but should not be used at scales greater (more detailed) than 1:750,000 (about twice as detailed as the original scale). The GIS data allows output as a single-country map (1:1,000,000 to 1:2,000,000 scale) or provincial and regional maps (about 1:750,000 scale) while retaining all significant digital information. In addition to fault location and style, the map shows time of most recent movement and estimates of slip rate (as a proxy for fault activity). Although as many as five categories of Quaternary faults can be depicted on the Western Hemisphere maps, only three categories were used in Ecuador:

Historic (generally <300 years depending on location),

Holocene and latest Pleistocene (<15,000 years or <15 ka),

Quaternary (<1,600,000 years or <1.6 Ma).

Categories for differentiating late Quaternary (<130 ka) and late and middle Quaternary (<750 ka) ruptures were not used owing to the general lack of stratigraphic and chronological control needed to make these age differentiations. Nevertheless, this categorical time scheme allows some flexibility in reporting between countries owing to the differing levels of investigation and abilities to date prehistoric faulting.

Three ranges of slip rates depicted by differing line thicknesses are shown on the map in order to differentiate known rates of fault activity:

>5 mm/yr—Plate-boundary faults and subduction zones,

1-5 mm/yr—Lesser strike-slip and major extensional or transpressional faults,

<1 mm/yr—Most extensional and intraplate faults.

Most faults in Ecuador with "unknown slip rates" are drawn with the <1 mm/yr line thickness.

Database

The purpose of the database is to provide fault data that can be readily accessed using a variety of search parameters. For this database, we anticipate that the user would want search-and-retrieve capabilities from a personal computer. The user may want to sort the data by such parameters as fault name, time of most recent movement (one of three categories), slip rate (one of four categories), sense of movement, or by multiple parameters.

The process of data compilation starts with data acquisition and synthesis. In the case of faults, the compiler must determine if the structure is a simple one, or if it qualifies as having sections (increased complexity of geometry or fault history). Then using the appropriate form, the compiler tabulates information on the fault’s parameters.

After this report is released, we will incorporate suggested changes and additions; then import the data to the computer database. Each of the fields is a potential search object. The use of a computer database program allows us to custom format the reporting of data and to collapse unused fields or notes. The basic fields are restricted to 256 characters, but we use the note option for more explanatory information (shown under comments in this report).

The fault and fold data will be released in several forms. This open-file report constitutes a traditional hard-copy catalog (database and map) for Ecuador. The Ecuador data will eventually be part of a larger relational computer database for the Western Hemisphere that should be available on the World Wide Web (WWW). This interactive WWW product allows the user to browse, sort, and print the data. However, we do not anticipate allowing the database to be altered using only the run-time WWW version of the database program.

DEFINITION OF DATABASE TERMS

The following terms,provide data for specialized fields, most of which will be searchable when the computer database is released. In addition specialized fields, more detailed information is provided in the "Comments" section that follows some fields. If a field is empty, marked unknown, or has been deleted, no pertinent information was found in the published literature. The following description provides definitions of fields (in alphabetic order) and indicates where various data, if known, can be found. Citations of references are in a traditional (USGS) format, although foreign language citations are as provided by the compilers.

Average dip General down-dip direction of the structure, where known.

Average strike The length-weighted average strike of the trace of the structure is reported in the northwest and northeast quadrants of the compass (i.e., N30°W, versus S30°E). The error limits that follow the strike are for all vectors contained with the trace of that particular fault or collection of faults. These values are included only to provide a general impression of the sinuosity or variability in strike of the mapped structures. Some fault zones include a number of faults with a wide variety of strikes, and thus the error limits are not meaningful.

Compiler, affiliation and date of compilation The name and affiliation of the person(s) primarily responsible for compilation or update of data presented for the structure. Also shown is the date when data were compiled for this project (e.g., January 1997).

Fault geometry This heading includes geographic information pertinent to the fault or fold being described. The data include length, average strike, average dip, and sense of movement.

Fault/fold name (see Name)

Fault/fold number (see Number)

Geomorphic expression General description of the structure’s geomorphic expression including information on the presence or absence of fault scarps, offset streams, monoclines, shutter ridges, associated landslides, etc.

Historical surface faulting When the timing of most recent movement on a fault is historic, then this field(s) describes evidence for surface faulting associated with historical earthquakes. Also included is seismological information for the historical earthquake.

Length This field specifies the end-to-end length of the Quaternary-age fault as measured from the most distal ends of the trace. The ends of overlapping or echelon traces are projected to a line defined by the average strike and the length is then determined from those projected end points. Also shown (in parentheses) is the cumulative length of all surface traces included in the fault, fault zone, or collection of faults.

Name (Fault name or Section name) The earliest referenced name for a structure or fault section (where appropriate) generally is given preference, except in cases where a more commonly accepted name is widely used in the recent literature. "Comments" may also contain other names and references in which they are used, the geographic limits of the structure, north to south or west to east, as shown in this compilation; various geographic limits that are different than in other studies are also included. Minor changes in original name may have been made for reasons of clarity or consistency (such as segment to section) where appropriate. We have found no faults in Ecuador that justify using the term “segment”, owing to a lack of precise timing information.

Number
Structure number The structure (fault or fold) is assigned a number that is preceded by a two character abbreviation (Ecuador fault number 1 is EC-01) that is unique to each of the countries in the Western Hemisphere. References to the same structure shown in other compilations, such as CO-01 or PE-01 are included in "Comments".
Section number An alpha character is assigned to the northernmost or westernmost section of a fault (e.g., fault EC-02 has two sections: EC-02A and EC-02B).

Number of sections (only used for faults with sections) Numeric value for number of sections (e.g., 2) defined in studies that do not meet the minimum requirements for segments established for this compilation. "Comments" include reference in which sections are discussed; if the term "segment" is used in the literature, an explanation of why "section" is used in the database is provided.

Recurrence interval Time interval in yr (based on historic data, calendar or calibrated radiocarbon dates), in 14C yr (based on uncalibrated radiocarbon dates), or in k.y. (thousand years, based on less precise dating methods, stratigraphy, or geomorphology). Unknown is shown if there is no published recurrence interval value. Alternative published recurrence intervals, starting with that which applies to the most recent time interval, are included in "Comments." Very few faults in Ecuador have established recurrence intervals.

References A bibliographic citation is included for all references pertinent to each structure. Papers published in Spanish are cited in Spanish, and may not conform to USGS style.

Section A geographic, geometric, structural portion of a fault or collection of faults that appear(s) to have a different character than adjacent portions of the fault (or fold). Typically, not enough information exists to show that this portion of the fault acts independently of adjacent portions, and thus does not qualify as a bona fide "segment" of a fault in a paleoseismic sense. There are no known faults with proven segments in Ecuador, although several faults are described as having sections. Further research is needed to document additional faults with sections or those with sections that may in fact be segments.

Sense of movement Includes thrust, less than 45° dip; reverse, greater than 45° dip; right-lateral strike-slip (dextral); left-lateral strike slip (sinistral); or normal faults. For oblique slip, the principle sense of movement is followed by secondary sense (i.e., dextral, normal).

Slip rate The primary field shows an actual value or one of several slip-rate categories used for the map part of this compilation: <1 mm/yr, 1-5 mm/yr, or >5 mm/yr. Very few faults in Ecuador have established slip rates. “Unknown" precedes the suspected slip-rate or slip rate category if no published slip rate is known. "Comments" may include a synopsis of published slip rates and pertinent documentation. Generally speaking, there are two types of slip rates. The first type is termed a “Geologic slip rate” and is derived from the age and amount of offset of surficial geologic deposits. These rates are not precise, but allow one to place broad limits on possible slip rates, and hence characterize the fault in one of the above-mentioned categories. Most slip rates from Ecuador are geologically determined. The second type of slip rate is termed a “Paleoseismic slip rate” and is derived from times of faulting events and amounts of offset of geologic datums or piercing points. This type of slip rate is more precise, but is rare owing to the extensive amount of work involved (i.e., detailed paleoseismologic studies involving trenching and numeric dating).

Synopsis and geologic setting This field provides a short summary that describes the level of study, provides a snapshot of the scope of data that follows in the database and provides a generalized perspective of the fault in terms of its regional geologic setting, amount of total offset, and general age of offset strata. Not all faults in the database have a synopsis and discussion of geologic setting.

Timing of most recent event (faulting or folding event) The primary field shows one of the two prehistoric time categories: latest Quaternary (Holocene and latest Pleistocene, <15 ka) or Quaternary (<1.6 Ma). This field may document historic surface faulting, although details of the earthquake related to the faulting will follow.

Type of studies This field briefly summarizes the types of studies conducted on the fault.

ACKNOWLEDGEMENTS

This project was supported by the USGS’s National Earthquake Hazards Reduction Program (NEHRP) and by the International Lithosphere Program (ILP) under the direction of Task Group II-2 (World Map of Major Active Faults). Carlos Costa provided coordination of the ILP efforts in South America. The Geology Department and Geophysical Institute of the National Polytechnic School (Departamento Geología y Instituto Geofísico, Escuela Politécnica Nacional), Quito, Ecuador, provided space, facilities, time, and technical assistance in order for the senior authors to complete this effort. In addition, they also provided meeting space for a previous ILP Task Group II-2 coordination meeting. We appreciate the thorough and constructive comments of Hans Diederix (formerly of International Institute for Aerospace Survey and Earth Sciences (ITC), Enschede, The Netherlands) who reviewed the manuscript and map.

REFERENCES CITED

Audemard, F.A., Machette, M.N., Dart, R.L., and Haller, K.M., 2000, Map and Database of Quaternary Faults in Venezuela and its Offshore Regions: U.S. Geological Survey Open-File Report 00-018, 76 p., 1 plate (1:2M scale).

Campbell, C.J., 1974, Ecuadorian Andes in Mesozoic-Cenozoic orogenic belt, data for orogenic studies: Geological Society of London Special Publication 4, p. 725-732.

Costa, C., Machette, M.N, Dart, R.L., Bastias, H.E., Paredes, J.D., Perucca, L.P., Tello, G.I., and Haller, K.M., 2000, Map and Database of Quaternary Faults and Folds in Argentina: U.S. Geological Survey Open-File Report 00-0108, 76 p., 90 p., 1 plate (1:4,000,000 scale).

Cowan, H., Machette, M.N., Haller, K.M., and Dart, R.L., 1998, Map and database of Quaternary faults and folds in Panama and its offshore regions: U.S. Geological Survey Open-File Report 98-779, 41 p., 1 plate (1:500,000 scale).

Cowan, Hugh, Machette, M.N., Amador, Xavier, Morgan, Karen S., Dart, R.L., and Bradley, Lee-Ann, 2000, Map and Database of Quaternary Faults and Folds in the Vicinity of Managua, Nicaragua: U.S. Geological Survey Open-File Report 00-0437, 61 p., 1 plate (1:750,000 scale).

Eguez, A., and Aspden, J., 1993, The Mesozoic-Cenozoic evolution of the Ecuadorian Andes: Second ISAG, Oxford (UK), p 179-182.

Gutscher, M.A., Malavieille, J., Lallemand, S., and Collot, J.Y., 1999, Tectonic segmentations of the North Andean margin—An impact of the Carnegie Ridge collision: Earth and Planetary Science Letters, v. 168, p. 255-270.

Haller, K.M., Machette, M.N., and Dart, R.L., 1993, Maps of Major Active Faults, Western Hemisphere; International Lithosphere Program (ILP) Project II-2: Guidelines for U.S. Database and Map: U.S. Geological Survey Open-File Report 93-338, 45 p.

Hey, R., 1977, Tectonic evolution of the Cocos-Nazca spreading center: Geological Society of America Bulletin, v. 88, p. 1404-1420.

Lavenu, A., Thiele, R., Machette, M.N., Dart, R.L., and Haller, K.M., 2000, Map and Database of Quaternary Faults and Folds in Bolovia and Chile: U.S. Geological Survey Open-File Report 00-0283, 38 p., 2 plates

Litherland, M., Aspden, J.A., and Jemielita, R.A., 1994, The metamorphic belts of Ecuador: Overseas Memoir of the British Geological Survey, No. 11.

Montero, W., Denyer, P., Barquero, R., Alvarado, G.E., Cowan, H., Machette, M.N., Haller, K.M., and Dart, R.L., 1998, Map and database of Quaternary faults and folds in Costa Rica and its offshore regions: U.S. Geological Survey Open-File Report 98-481, 63 p., 1 plate (1:750,000 scale).

Paris, Gabriel, Machette, M.N., Dart, R.L., and Haller, K.M., 2000, Map and Database of Quaternary Faults and Folds in Colombia and its Offshore Regions: U.S. Geological Survey Open-File Report 00-0284, 61 p., 1 plate (1:2,500,000 scale).

Pennington, W.D., 1981, Subduction of the eastern Panama basin and seismotectonics of northwestern South America: Journal of Geophysical Research, v. 86, p. 10753-10770.

Soulas, J.P., Eguez, A., Yepes, H., y Pérez, V.H., 1991, Tectónica activa y riesgo sísmico en Los Andes Ecuatorianos y el extremo sur de Colombia: Boletin Geologia Ecuatoriano, v. 2, no. 1, p. 3-11.

DATABASE OF FAULTS AND FOLDS

EC-01, San Lorenzo Lineament

FAULT NUMBER: EC-01

FAULT NAME: San Lorenzo (lineament)

SYNOPSIS AND GEOLOGIC SETTING: This lineament appears to control the shoreline around the mouths of the Cayapas and Santiago rivers. The lineament is likely a fault in bedrock, although Quaternary movement is not proven.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation

FAULT GEOMETRY
LENGTH: 21.9 km (21.9 km)
AVERAGE STRIKE: N31°E±0°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: Linear morphology of the shore line.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)
Comments: Quaternary movement is not proven.

EC-02, Esmeraldas Fault

FAULT NUMBER: EC-02

FAULT NAME: Esmeraldas

SYNOPSIS AND GEOLOGIC SETTING: This structure controls the linear drainage of the Esmeraldas River. Previously, it was inferred to be a major structure that crosses the Andean chain.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation and local field control.

FAULT GEOMETRY:
LENGTH: 58.4 km (63.6 km)
AVERAGE STRIKE: N26°W±13°

NUMBER OF SECTIONS: 2

EC-02a, Northern section

SECTION NUMBER: EC-02a

SECTION NAME: Northern

SECTION GEOMETRY
LENGTH: 21.3 km (21.6 km)
AVERAGE STRIKE: N34°W±12°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: Linear control of the main drainage.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-02b, Southern section

SECTION NUMBER: EC-02b

SECTION NAME: Southern

SECTION GEOMETRY
LENGTH: 41.1 km (42.0 km)
AVERAGE STRIKE: N22°W±13°
AVERAGE DIP: Unknown angle, dips east
SENSE OF MOVEMENT: Transpressional with probable left-lateral (sinistral) and reverse movements.

GEOMORPHIC EXPRESSION: Irregular curved scarps and control of drainages. The asymmetric development of alluvial terraces suggests uplift of the eastern block.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-03, RÍo CanandÉ

FAULT NUMBER: EC-03

FAULT NAME: Río Canandé

SYNOPSIS AND GEOLOGIC SETTING: This fault partially forms the northern boundary of the main fore-arc basin in Ecuador. The structure cuts an anomalous arm of the Cordillera Oriental (Western) and towards the north it seems to control the limit of the Borbón basin and the Andean foothills (Pérez and others, 1994; Alvarado, 19980

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretation of radar images.

FAULT GEOMETRY
LENGTH: 59.6 km (62.3 km)
AVERAGE STRIKE: N74°E±19°

NUMBER OF SECTIONS: 3

REFERENCES

Alvarado, A., 1998, Variation du champs de contrainte et de deformation et quantification des deformations actives du bloc Côtiere de l’Equateur: DEA, Paris Sud Orsay, Unpublished report, 54 p.

Pérez, V.H., Hibsch, C., Alvarado, A. and Yepes H., 1994, Paleosismicidad de la ciudad de Quito (Ecuador) a través del análisis de la paleolicuación Cuaternaria: Estudios de Geografía, Quito, v. 6, p. 31-46.

EC-03a, Western section

SECTION NUMBER: EC-03a

SECTION NAME: Western

SECTION GEOMETRY
LENGTH: 16.0 km (16.5 km)
AVERAGE STRIKE: N83°W±18°
AVERAGE DIP: Unknown angle, dips to the south
SENSE OF MOVEMENT: Normal with right-lateral (dextral) component.

GEOMORPHIC EXPRESSION: Forms discontinuos scarps with triangular facets along fault trace, which is mostly concealed. The drainages are deflected in same direction as the scarp (right lateral).

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma).

EC-03b, Central section

SECTION NUMBER: EC-03b

SECTION NAME: Central

SECTION GEOMETRY
LENGTH: 25.8 km (26.2 km)
AVERAGE STRIKE: N71°E±10°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Right-lateral (dextral)

GEOMORPHIC EXPRESSION: Offset of drainages and topographic control along most of the fault trace.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-03c, Eastern section

SECTION NUMBER: EC-03c

SECTION NAME: Eastern

SECTION GEOMETRY
LENGTH: 19.7 km (19.6 km)
AVERAGE STRIKE: N60°E±3°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Probable right-lateral (dextral)

GEOMORPHIC EXPRESSION: Linear control of the topography and drainages along parts of the fault trace, which is mostly concealed.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-04, Galera fault

FAULT NUMBER: EC-04

FAULT NAME: Galera

SYNOPSIS AND GEOLOGIC SETTING: This is a series of subparallel structures that appears to affect mostly Miocene-Pliocene rocks, but the faults appear to deform Quaternary marine terraces as seen on radar images. The easternmost fault trace is shown as a mostly discontinuous structure, whereas the two western faults are shown as mainly concealed or inferred on the map.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretationof radar images.

FAULT GEOMETRY
LENGTH: 25.1 km (62.3 km)
AVERAGE STRIKE: N55°E±4°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Dextral with normal component

GEOMORPHIC EXPRESSION: Fault scarps and linear control of topography and drainage is most prominent on the easternmost fault trace.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-05, Buga fault

FAULT NUMBER: EC-05

FAULT NAME: Buga

SYNOPSIS AND GEOLOGIC SETTING: This fault forms has a weak expression (lineament) on radar images. It may represent a northward extension of the Cañaveral fault [EC-07] , which is one of the most important fault systems in NW Ecuador.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politecnica Nacional, Departmento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation

FAULT GEOMETRY
LENGTH: N13°E ±13°
AVERAGE STRIKE: 24.6 km (24.9 km)
AVERAGE DIP: Unknown angle to the west
SENSE OF MOVEMENT: Reverse

GEOMORPHIC EXPRESSION: Unknown

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-06, MACHE Lineament

FAULT NUMBER: EC-06

FAULT NAME: Mache (lineament)

SYNOPSIS AND GEOLOGIC SETTING: This lineament is only inferred from radar images, and Quaternary faulting is not proven.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretation of radar images.

FAULT GEOMETRY
LENGTH: 57.5 km (66.7 km)
AVERAGE STRIKE: N39°E±15°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: It forms a weak lineament on radar images.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-07, CaÑaveral Fault

FAULT NUMBER: EC-07

FAULT NAME: Cañaveral

SYNOPSIS AND GEOLOGIC SETTING: The structure belongs to the most important fault system in NW Ecuador. It controls the uplift of basement rocks and the formation of the coastal mountains. The southern section of the Cañaveral fault system [EC-07c] is separated from the central section by a 20 km gap. It has previously been named the Jama fault, but is considered herein to be a discontinuous extension of the Cañaveral fault.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Radar and photo interpretation and field studies.

FAULT GEOMETRY
LENGTH: 137.7 km (173.8 km)
AVERAGE STRIKE: N37°E±16°

NUMBER OF SECTION: 3

EC-07a, Northern section

SECTION NUMBER: EC-07a

SECTION NAME: Northern

SECTION GEOMETRY
LENGTH: 37.5 km (52.7 km)
AVERAGE STRIKE: N31°E±19°
AVERAGE DIP: Probable high angle, dips to the west.
SENSE OF MOVEMENT: Reverse with dextral component

GEOMORPHIC EXPRESSION: Forms discontinuos scarps and controls the course of rivers. Trace shown as mainly concealed owing to discontinuos nature of expression.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-07b, Central section

SECTION NUMBER: EC-07b

SECTION NAME: Central

SECTION GEOMETRY
LENGTH: 34.2 km (34.5 km)
AVERAGE STRIKE: N53°E±10°
AVERAGE DIP: Unknown angle, down to southeast
SENSE OF MOVEMENT: Transtensional; right lateral and normal components.

GEOMORPHIC EXPRESSION: Streams flow along the trace of the fault suggesting major structural control owing to transtensional motion. Topography along a large portion of the fault shows a pronounced scarp and fault defines an extensional basin.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma).

EC-07c, Jama section

SECTION NUMBER: EC-07c

SECTION NAME: Southern

SECTION GEOMETRY
LENGTH: 46.7 km (71.2 km)
AVERAGE STRIKE: N37°E±12°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: This fault forms a well defined lineament (on radar images) that controls the drainage of El Venado River. Elongated hills along the lineament may be shutter ridges related to transpressional movement, although this sense of movement is not well documented.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-07d, San Isidro section

SECTION NUMBER: EC-07d

SECTION NAME: San Isidro

SECTION GEOMETRY
LENGTH: 15.1 km (15.4 km)
AVERAGE STRIKE: N18°E±11°
AVERAGE DIP: Unknown, dips to west
SENSE OF MOVEMENT: Normal with dextral component

GEOMORPHIC EXPRESSION: The fault along Estero Hondo Creek affects Quaternary terraces that show meter-size displacements.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-08, QuinindÉ FAULT

FAULT NUMBER: EC-08

FAULT NAME: Quinindé

SYNOPSIS AND GEOLOGIC SETTING: This structure borders the Quaternary continental sedimentary Santo Domingo basin of the fore-arc coastal zone. The coastal mountains (including their core of basement rock) appears to be uplifted and is limited by this structure. Thus, this fault probably has an ancient heritage.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretationof radar images.

FAULT GEOMETRY
LENGTH: 78.2 km (101.2 km)
AVERAGE STRIKE: N25°E±15°
AVERAGE DIP: Unknown angle, dips to the west
SENSE OF MOVEMENT: Probable reverse transpressive.

GEOMORPHIC EXPRESSION: The Quinindé River flows along the trace of the fault. It forms the western limit of the Santo Domingo basin.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-10, BahÍa Fault

FAULT NUMBER: EC-10

FAULT NAME: Bahía

SYNOPSIS AND GEOLOGIC SETTING: Tertiary sediments appear uplifted to the east of the fault. Elongated marine terraces are also involved with this structure.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Radar and photo interpretation

FAULT GEOMETRY
LENGTH: 43.4 km (46.2 km)
AVERAGE STRIKE: N11°W±20°

NUMBER OF SECTIONS 2

EC-10a, Northern section

SECTION NUMBER: EC-10a

SECTION NAME: Northern

SECTION GEOMETRY
LENGTH: 22.2 km (22.4 km)
AVERAGE STRIKE: N24°W±10°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Possible left-lateral

GEOMORPHIC EXPRESSION: It controls the shoreline and forms well developed scarps with triangular facets along the beach.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-10b, Southern section

SECTION NUMBER: EC-10b

SECTION NAME: Southern

SECTION GEOMETRY
LENGTH: 22.2 km (23.8 km)
AVERAGE STRIKE: N1E°±23°
AVERAGE DIP: Unknown, dips to the west
SENSE OF MOVEMENT: Possible reverse to transpressive

GEOMORPHIC EXPRESSION: It forms a weak irregular fault trace suggesting reverse movement.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-11, Calceta fault

FAULT NUMBER: EC-11

FAULT NAME: Calceta

SYNOPSIS AND GEOLOGIC SETTING: The structure forms the west boundary of the coastal mountains. It affects mainly Tertiary sedimentary rocks, but morphologic features along the fault suggest Quaternary activity. The trace of the fault is shown as mainly inferred or concealed.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretationof radar images.

FAULT GEOMETRY
LENGTH: 50.3 km (51.7 km)
AVERAGE STRIKE: N29°E±15°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: The structure forms a lineament along the west margin of the Coastal Range. Unnamed morphologic features along the fault suggest Quaternary activity.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-12, Daule fault

FAULT NUMBER: EC-12

FAULT NAME: Daule

SYNOPSIS AND GEOLOGIC SETTING: The structure constitutes the eastern boundary of the coastal mountains. It probably extends toward the north and may be associated with the Quinindé fault [EC-08]. Although most of the trace of the Daule fault is concealed, there is some seismicity associated with it.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretation of radar images.

FAULT GEOMETRY
LENGTH: 77.9 km (79.9 km)
AVERAGE STRIKE: N32°E±14°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: The Daule River appears to be controlled by this fault where it borders the Quaternary Daule Basin.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-13, Buena Fe fault

FAULT NUMBER: EC-13

FAULT NAME: Buena Fe

SYNOPSIS AND GEOLOGIC SETTING: This structure probably controls alluvial sedimentation along the Quevedo-Babahoyo Basin. The fault’s expression is not clear because river erosion has destroyed all morphologic evidence of recent movement.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretationof radar images.

FAULT GEOMETRY
LENGTH: 61.1 km (62.9 km)
AVERAGE STRIKE: N38°E±15°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: It forms a weak lineament on radar images . However, the fault’s expression is not clear because river erosion has destroyed all morphologic evidence of recent movement.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-14, Jipijapa Fault

FAULT NUMBER: EC-14

FAULT NAME: Jipijapa

SYNOPSIS AND GEOLOGIC SETTING: The structure borders the coastal hills toward the west, where oceanic basement rock appears uplifted suggesting an ancient activity to the fault. Collision of the Carnegie Ridge (Nazca Plate) with the South American Plate could be related to the kinematics of this fault. The Julcuy fault constitutes the southern section of the Jipijapa fault.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretationof radar images.

FAULT GEOMETRY
LENGTH: 43.0 km (39.8 km)
AVERAGE STRIKE: N18°E±11°
NUMBER OF SECTIONS: 2

EC-14A, Jipijapa section

SECTION NUMBER: EC-14A

SECTION NAME: Jipijapa

SECTION GEOMETRY
LENGTH: 23.6 km (23.8 km)
AVERAGE STRIKE: N13°E±10°
AVERAGE DIP: Unknown angle, dips to the west
SENSE OF MOVEMENT: Reverse (inferred)

GEOMORPHIC EXPRESSION: Anomalous border of basin showing irregular escarpment related to inferred reverse fault.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-14B, Julcuy (fault) section

SECTION NUMBER: EC-14B

SECTION NAME: Julcuy(fault)

SECTION GEOMETRY
LENGTH: 15.9 km (16.0 km)
AVERAGE STRIKE: N27°E±9°
AVERAGE DIP: Unknown angle, dips to the west
SENSE OF MOVEMENT: Reverse (inferred)

GEOMORPHIC EXPRESSION: Extension of the Jipijapa [EC-14a] section. Forms escarpment related to reverse(?) faulting.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-15, RÍO COLIMES fault

FAULT NUMBER: EC-15

FAULT NAME: Río Colimes

SYNOPSIS AND GEOLOGIC SETTING: The structure limits the youngest basin of the continental alluvial deposits of the Daule River.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretation of radar images.

FAULT GEOMETRY
LENGTH: 27.2 km (27.3 km)
AVERAGE STRIKE: N53°E±6°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: Drainages are fault controlled (form straight lineament).

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-16, Colonche Fault ZONE

FAULT NUMBER: EC-16

FAULT NAME: Colonche (fault zone)

SYNOPSIS AND GEOLOGIC SETTING: The Colonche fault zone border the Chongón-Colonche Cordillera (Mountains) on the south. It is probably a reactivated fault associated with the formation of the Tertiary Progreso Basin, involving tectonic inversión. Oceanic basement rocks are uplifted on the north. The fault zone has four traces that extend for >100 km in a southeast direction from near the Pacific coast to Guayaquil.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretationof radar images.

FAULT GEOMETRY
LENGTH: 106.4 km (87.9 km)
AVERAGE STRIKE: N59°W±22°

NUMBER OF SECTIONS: 4

EC-16a, Northwestern section

SECTION NUMBER: EC-16a

SECTION NAME: Northwestern

SECTION GEOMETRY
LENGTH: 10.3 km (10.5 km)
AVERAGE STRIKE: N44°W±13°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Probable reverse

GEOMORPHIC EXPRESSION: It forms a weak curved trace suggesting reverse faulting.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-16b, Northern section

SECTION NUMBER: EC-16b

SECTION NAME: Northern

SECTION GEOMETRY
LENGTH: 22.8 km (24.1 km)
AVERAGE STRIKE: N39°W±21°
AVERAGE DIP: Probably to the northeast.
SENSE OF MOVEMENT: Reverse to transpressional.

GEOMORPHIC EXPRESSION: Foothills uplifted along curved fault trace and offset drainages suggest a reverse to transpressional fault escarpment.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-16c, Central section

SECTION NUMBER: EC-16c

SECTION NAME: Central

SECTION GEOMETRY
LENGTH: 20.9 km (20.9 km)
AVERAGE STRIKE: N58°W±4°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Probably dominant left lateral (sinistral)

GEOMORPHIC EXPRESSION: The structure forms a weak but conspicuous straight lineament where drainages show left-lateral displacements.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-16d, Southern section

SECTION NUMBER: EC-16d

SECTION NAME: Southern

SECTION GEOMETRY
LENGTH: 32.1 km (32.4 km)
AVERAGE STRIKE: N79°W±9°
AVERAGE DIP: Unknown, dips to the north
SENSE OF MOVEMENT: Reverse

GEOMORPHIC EXPRESSION: Forms curved trace where the basement is uplifted towards the north. Irregular trace of escarpment suggests dominant reverse faulting.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-17, Carrizal fault

FAULT NUMBER: EC-17

FAULT NAME: Carrizal

SYNOPSIS AND GEOLOGIC SETTING: This fault constitutes an old reactivated structure related to the Progreso basin development (Toro, 1994). It affects Neogene rocks (Benítes, 1995), but Quaternary movement is suspected from the linear control of stream drainages. The trace of the fault is shown as concealed for its entire length.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretation of radar images and seismic records.

FAULT GEOMETRY
LENGTH: 66.0 km (67.9 km)
AVERAGE STRIKE: N53°W±15°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: Linear control of the drainages suggests Quaternary activity of this structure.

RECURRENCE INTERVAL: Unknown

SLIP RATE: <1 mm/yr
Comments: Placed in the <1 mm/yr category, but a slip rate of <0.2 mm/yr was determined from a vertical offset of 1,000 m since Paleogene times (Benítes, 1995). This rate may not apply to the Quaternary.

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

REFERENCES

Benítes, S., 1995, Evolution geodynamique de la province Cotiere sur-equatorienne au Cretace superieur-Teriaire: Grenoble, France, Université Joseph Fournier-Grenoble 1, 221 p.

Toro, J., 1994, Geodinámica de la cuenca sedimentaria Progreso, Provincia de Guayas: Quito, Ecuador, Escuela Politécnica Nacional, thesis, 428 p.

EC-18, La Cruz fault

FAULT NAME: La Cruz

SYNOPSIS AND GEOLOGIC SETTING: Recognized as a Neogene fault related to the formationa of the Progreso basin, with possible reactivation during Pleistocene time.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretation of radar images, seismic records, and microtectonic studies.

FAULT GEOMETRY
LENGTH: 47.8 km (47.8 km)
AVERAGE STRIKE: N50°W±0°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Dextral
Comments: Determined from geophysical studies.

GEOMORPHIC EXPRESSION: Forms a nearly straight lineament which is shown as a concealed or inferred fault on the map.

RECURRENCE INTERVAL: Unknown

SLIP RATE: <1 mm/yr
Comments: Placed in the <1 mm/yr category, but a slip rate of <0.2 mm/yr was determined from vertical offset of 3,000 m since Oligocene time (Benítes, 1995); rate may not be applicable for the Quaternary.

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)
Comments: This fault shows evidence of microseismic activity.

REFERENCES

Benítes, S., 1995, Evolution geodynamique de la province Cotiere sur-equatorienne au Cretace superieur-Teriaire: Grenoble, France, Université Joseph Fournier-Grenoble 1, thesis, 221 p.

Toro, J., 1994, Geodinámica de la cuenca sedimentaria Progreso, Provincia de Guayas: Quito, Ecuador, Escuela Politécnica Nacional, thesis, 428 p.

EC-19, Chanduy fault

FAULT NUMBER: EC-19

FAULT NAME: Chanduy

SYNOPSIS AND GEOLOGIC SETTING: This northwest-trending fault parallels the northern coast of the Gulf of Guayaquil and may be similar to the Posorja fault [EC-19], which is a normal fault system within the Jambelí basin. Marine terraces appear to be defored by this fault.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Interpretation of radar images.

FAULT GEOMETRY
LENGTH: 34.4 km (34.7 km)
AVERAGE STRIKE: N45°W±9°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: Fault forms a straight shoreline and controls drainages as they approach the beach (coast). Shown as a concealed or inferred fault on the map

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-20, Posorja fault

FAULT NUMBER: EC-20

FAULT NAME: Posorja

SYNOPSIS AND GEOLOGIC SETTING: This northwest-trending structure is related to the normal fault system within the Jambelí basin. This fault system allows the opening of Guayaquil Gulf and is probably associated to the Pallatanga fault zone [EC-50].

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Bathymetric and seismic studies (Benites, 1995; Lions, 1995).

FAULT GEOMETRY
LENGTH: 73.5 km (75.0 km)
AVERAGE STRIKE: N74°W±15°
AVERAGE DIP: Unknown angle, dips to the south
SENSE OF MOVEMENT: Normal

GEOMORPHIC EXPRESSION: Although everywhere submerged, it forms submarine scarps.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

REFERENCES

Benites, S., 1995, Evolution geodynamique de la province Cotiere sur-equatorienne au Cretace superieur-Teriaire: Grenoble, France, Université Joseph Fournier-Grenoble 1, thesis, 221 p.

Lions, R., 1995, Evolution geodynamique de un bassin d´avant-arc neogene en contexte décrochant—L'ouverture du Golfe de Guayaquil: Nice, France, Université de Nice-Sophia Antipolis, thesis DEA, p. 35

EC-21, JambelÍ Fault

FAULT NUMBER: EC-21

FAULT NAME: Jambelí

SYNOPSIS AND GEOLOGIC SETTING: The fault is probably a branch of the Pallatanga fault zone [EC-50].

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Bathymetric and seismic studies.

FAULT GEOMETRY
LENGTH: 16.9 km (16.9km)
AVERAGE STRIKE: N58°E±0°
AVERAGE DIP: Unknown angle, dips to the south
SENSE OF MOVEMENT: Normal

GEOMORPHIC EXPRESSION: Although everywhere submerged, it forms submarine scarps.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

REFERENCES

Benites, S., 1995, Evolution geodynamique de la province Cotiere sur-equatorienne au Cretace superieur-Teriaire: Grenoble, France, Université Joseph Fournier-Grenoble 1, thesis, 221 p.

EC-22, PunÁ Fault

FAULT NUMBER: EC-22

FAULT NAME: Puná

SYNOPSIS AND GEOLOGIC SETTING: This northeast-trending fault has been interpreted by Iglesias and others (1991) as part of the Puná-Milagro-Chazo Juan fault system. It bisects the Zambapala Ridge, which is formed by older reverse faults. The Puná fault juxtaposes sediment of the Tablazo Formation (Pleistocene?) against sediment of the Puná Formation (Pleistocene) (Benites, 1995). Interestingly, there is a pull-apart basin on the top of ridge suggesting a sequence of transtensional and transpressional events (Lions, 1995).

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Radar and satellite images.

FAULT GEOMETRY
LENGTH: 43.9 km (43.9 km)
AVERAGE STRIKE: N46°E±0°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Dextral

GEOMORPHIC EXPRESSION: It forms an elongated ridge (Zambapala), fault scarps, and a pull-apart basin on top of the ridge.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

REFERENCES

Benites, S., 1995, Evolution geodynamique de la province Cotiere sur-equatorienne au Cretace superieur-Teriaire: Grenoble, France, Université Joseph Fournier-Grenoble 1, thesis, 221 p.

EC-23, San Isidro fault

FAULT NUMBER: EC-23

FAULT NAME: San Isidro

SYNOPSIS AND GEOLOGIC SETTING: This northeast-trending fault has been interpreted by Soulas and others (1991) as a prolongation of the Colombian Cauca-Patía fault system, which is part of the Romeral fault system [CO-15] in Colombia. The San Isidro fault displaces late Pleistocene glacial moraines and other Quaternary deposits. It may be associated with El Angel fault [EC-24], although they are separated by a 15-km-long gap in faulting.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation and field studies.

FAULT GEOMETRY
LENGTH: 11.7 km (11.7 km)
AVERAGE STRIKE: N36°E±5°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Probable strike slip (dextral)
Comments: Faults to the north and south with the same orientation are known to be dextral.

GEOMORPHIC EXPRESSION: The fault is described as having benches, offset drainages and shutter ridges, all along a clear trace of fault.

RECURRENCE INTERVAL: 1,000-2,000 years
Comments: The above interval has been defined for the whole fault, and this recurrence is believed to be associated with an earthquake having a maximum Ms of 6.9 (Soulas and others, 1991).

SLIP RATE: 0.2-1.0 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Holocene and post glacial (<15 ka)
Comments: It displaces late Pleistocene glacial moraines and other Quaternary deposits.

REFERENCES

Soulas, J.P., Eguez, A., Yepes, H., y Pérez, V.H., 1991, Tectónica activa y riesgo sísmico en Los Andes Ecuatorianos y el extremo sur de Colombia: Bol. Geol. Ecuat., v. 2, no. 1, p. 3-11.

EC-24, El Angel Fault

FAULT NUMBER: EC-24

FAULT NAME: El Angel

SYNOPSIS AND GEOLOGIC SETTING: This northeast-trending fault has been interpreted by Soulas and others (1991) as a prolongation of the Colombian Cauca-Patía fault system. It displaces late Pleistocene glacial glacial moraines and other Quaternary deposits. It may be associated with San Isidro fault [EC-23], although they are separated by a 15-km-long gap in faulting.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation and field control.

SECTION GEOMETRY
LENGTH: 26.3 km (26.3 km)
AVERAGE STRIKE: N43°E±3°
AVERAGE DIP: Unknown angle, dips to the northwest
SENSE OF MOVEMENT: Reverse, strike slip(?) dextral
Comments: Faults to the north and south with the same orientation are known to be dextral.

GEOMORPHIC EXPRESSION: Northeast of El Angel (village), the fault forms some sag ponds, offset hills, and confined (closed) depressions, all of which suggest young (Holocene) movement with a component of dextral motion.

RECURRENCE INTERVAL: 1,000-2,000 years
Comments: The above interval has been indicated for the whole fault, and is believed to be associated with the maximum earthquake magnitude of 6.9 Ms (Soulas and others, 1991).

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Holocene and post glacial (<15 ka)
Comments: It displaces late Pleistocene glacial glacial moraines and other Quaternary deposits.

REFERENCES

Soulas, J.P., Eguez, A., Yepes, H., y Pérez, V.H., 1991, Tectónica activa y riesgo sísmico en Los Andes Ecuatorianos y el extremo sur de Colombia: Bol. Geol. Ecuat., v. 2, no. 1, p. 3-11.

EC-25, RÍo Ambi fault

FAULT NUMBER: EC-25

FAULT NAME: Río Ambi

SYNOPSIS AND GEOLOGIC SETTING: This northeast-trending structure controls the western boundary of the sedimentary Pliocene Chota basin. It mainly affects Pliocene-Quaternary volcanic deposits.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation.

FAULT GEOMETRY
LENGTH: 15.6 km (15.9 km)
AVERAGE STRIKE: N31°E±15°
AVERAGE DIP: Unknown angle, dips to the WNW
SENSE OF MOVEMENT: Reverse, strike-slip(?) dextral
Comments: Faults to the north and south with the same orientation are known to be dextral.

GEOMORPHIC EXPRESSION: The fault forms scarps and elongated hills along the Río Ambi Valley.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-26, Otavalo fault

FAULT NUMBER: EC-26

FAULT NAME: Otavalo

SYNOPSIS AND GEOLOGIC SETTING: Reported and mapped by Soulas (1988) on the west side of Otavalo (village). Its trend is NE-SW. At the north end, this fault continues to Atuntaqui (village), which suggests a left step with the San Isidro fault [EC-24] farther north. At the south end, this fault probably ends at a small transpressive basin near the Chavezpamba fault zone (Eguez and Yepes, 1993).

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation and field control.

FAULT GEOMETRY
LENGTH: 21.3 km (21.3 km)
AVERAGE STRIKE: N42°E±4°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Dextral

GEOMORPHIC EXPRESSION: Benches and shutter ridges have been described along the fault.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

REFERENCES

Eguez, A., Yepes, H., 1993, Estudio sismotectónico y de peligro sísmico para el proyecto hidroléctrico Chespi: Escuela Politécnica Nacional, Instituto Geofísico (inédito).

Soulas, J.P., 1988, Informe de misión en el Ecuador., Proyecto UNDRO-EPN: Programa de prevención y planificación para desastres en el Ecuador y países vecinos: Geneve, Switzerland, UNDRO. p. 21.

EC-27, Billecocha-Huyrapungo fault

FAULT NUMBER: EC-27

FAULT NAME: Billecocha-Huyrapungo

SYNOPSIS AND GEOLOGIC SETTING: The Billecocha-Huyrapungo fault has two sections, each with different apparent sense of movement. The Billecocha section is observed on an eroded plateau that is underlain (formed) by late Miocene and Pliocene volcanic deposits. This plateau is located east of an asymmetric anticline (fold). It is partially covered by Quaternary lava flows and volcanic material from the Cotacachi and Yanaurcu volcanoes. The morphology of the plateau was shaped by the last glaciation (ca. 15 ka) and subsequently smoothed by deposition of Holocene volcanic deposits (Ego and others, 1995).

The Huayrapungo section has been described as a prolongation of the Billecocha section by Eguez and others (1993). This section extends from the Cambugán River on the south to the Muyurcu volcanic domes (probably Pleistocene) on the north, thus having a length of about 30 km. At the south end, traces of this fault section form a horse-tail rupture pattern, with a N-S reverse secondary fault (motion determined from kinematics; Eguez and others, 1993).

Ego and others (1995) interpreted the Billecocha section as a normal fault caused by gravitational effects. Conversely, Eguez and others (1993) interpret the Huayrapungo section as a strike-slip fault of tectonic origin.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Inspection of SPOT images, photo interpretation, as well as fieldwork and microtectonic studies.

FAULT GEOMETRY
LENGTH: 33.2 km (21.9 km)
AVERAGE STRIKE: N33°E±8°

NUMBER OF SECTIONS: 2

EC-27a, Billecocha section

SECTION NUMBER: EC-27a

SECTION NAME: Billecocha

SECTION GEOMETRY
LENGTH: 7.0 km (7.0 km)
AVERAGE STRIKE: N25°E±4°
AVERAGE DIP: Unknown, dips to southeast
SENSE OF MOVEMENT: Normal(?)
Comments: Ego and others (1995) interpreted the Billecocha section as a normal fault caused by gravitational effects (landsliding). The geomorphology, structural setting, and southern (Huayrapungo) section suggest that the fault could have strike-slip movement.

GEOMORPHIC EXPRESSION: The fault forms scarps, sag ponds, and offset drainages. The latter features are suggestive of strike slip movement, but this may be an artifact of terminalogy (sag pond versus ponded drainage) rather than origin.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Holocene and post glacial (<15 ka)
Comentarios: On the basis of the morphology of the fault scarp, Ego and others (1995) suggested only one movement, which was dated between 5,700 and 10,000 yrs B.P.

EC-27b, Huayrapungo Section

SECTION NUMBER: EC-27b

SECTION NAME: Huayrapungo

SECTION GEOMETRY
LENGTH: 14.9 km (14.9 km)
AVERAGE STRIKE: N37°E±4°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Dextral
Comments: The faults kinematics have been determined by microtectonic analysis (Eguez and others, 1993) and its structural setting within a larger system of dextral faults.

GEOMORPHIC EXPRESSION: Fault is characterized by scarps showing triangular facets along linear valleys. Although triangular facets are not entirely diagnostic of faulting, they are believed to be the result of strike slip movement.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

REFERENCES

Ego, F., Sebrier, M., Carey-Gailhardis, E., Beate, B., 1995, Are the Billecocha normal faults revealing of extension due to lithospheric body forces in northern Andes (Ecuador)?: Orsay, France, Université de Paris-Sud, thesis, p. 209

Eguez, A., y Yepes, H., 1993, Estudios sismotectónicos y de peligro sísmico para el proyecto hidroléctrico Chespi: Escuela Politécnica Nacional, Instituto Geofísico (inédito).

EC-28, Apuela fault

FAULT NUMBER: EC-28

FAULT NAME: Apuela

SYNOPSIS AND GEOLOGIC SETTING: This fault partially disturbs the contact between Miocene Apuela intrusive rocks and the Eocene Macuchi and Unacota formations. However, the Apuela fault affects Pleistocene alluvial and glacial deposits. This fault has a sinuous pattern along the Apuela and Intag River valleys. Southward, the fault terminates 7 km west of the Nanegalito fault [EC-29].

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES Photo interpretation and fieldwork.

FAULT GEOMETRY
LENGTH: 53.8 km (75.0 km)
AVERAGE STRIKE: N48°E±11°

NUMBER OF SECTIONS: 3

EC-28a, Northeastern section

SECTION NUMBER: EC-28a

SECTION NAME: Northeastern

SECTION GEOMETRY
LENGTH: 25.4 km (25.5 km)
AVERAGE STRIKE: N50°E±12°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Dextral

GEOMORPHIC EXPRESSION: Fault offsets and blocks drainages. Fault trace shown as discontinuos.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-28b, Central section

SECTION NUMBER: EC-28b

SECTION NAME: Central

SECTION GEOMETRY
LENGTH: 20.4 km (20.4 km)
AVERAGE STRIKE: N49°E±7°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Dextral
Comments: Determined from offset drainages.

GEOMORPHIC EXPRESSION: Fault offsets and blocks drainages along most of its trace. Shown as mostly continuous trace on the map.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-28c, Southern section

SECTION NUMBER: EC-28c

SECTION NAME: Southern

SECTION GEOMETRY
LENGTH: 28.4 km (29.1 km)
AVERAGE STRIKE: N46°E±14°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Unknown

GEOMORPHIC EXPRESSION: Poorly expressed, shown as concealed along its trace.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

REFERENCES

Eguez, A., Yepes, H., 1993, Estudios sismotectónicos y de peligro sísmico para el proyecto hidroléctrico Chespi: Escuela Politécnica Nacional, Instituto Geofísico (inédito).

EC-29, Nanegalito fault zone

FAULT NUMBER: EC-29

FAULT NAME: Nanegalito (zone)

SYNOPSIS AND GEOLOGIC SETTING: This fault zone is observed from the Guayllabamba River in the north, to Mindo (village) in the south and is generally about 1.5 km wide. To the north, it continues to near the Quinde and Azabí Rivers, where some evidence of fault control can be observed. Near Nanegalito (village), this fault has caused 2 km of dextral offset of the Alambi River. It also affects the contact of the Nanegalito intrusive body with surrounding rocks. Colluvial deposits of Pliocene-Pleistocene age are faulted.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation, fieldwork, and microtectonic studies.

FAULT GEOMETRY
LENGTH: 43.6 km (49.1 km)
AVERAGE STRIKE: N37°E±8°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Dextral
Comments: Determined from 2 km of long-term offset of the Alambi River.

GEOMORPHIC EXPRESSION: Fault forms trenches, ridges, and triangular facets; all are indicators of young movement.

RECURRENCE INTERVAL: Unknown

SLIP RATE: 1-5 mm/yr
Comments: Inferred from estimated offset of drainages (basis of age is not stated).

TIME OF MOST RECENT OF MOVEMENT: Holocene and post glacial (<15 ka)
Comments: Inferred from young geomorphic expression and high estimated rate of slip.

REFERENCES

Eguez, A., Yepes, H., 1993, Estudios sismotectónicos y de peligro sísmico para el proyecto hidroléctrico Chespi: Escuela Politécnica Nacional, Instituto Geofísico (inédito).

EC-30, El Cinto fault

FAULT NUMBER: EC-30

FAULT NAME: El Cinto

SYNOPSIS AND GEOLOGIC SETTING: The structure affects volcanic deposits of the Quaternary Pichincha and Atacazo volcanoes.

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation and field studies.

FAULT GEOMETRY
LENGTH: 24.4 km (20.4 km)
AVERAGE STRIKE: N43°W±13°

NUMBER OF SECTIONS: 2

EC-30a, GuayacÁn section

SECTION NUMBER: EC-30a

SECTION NAME: Guayacán

SECTION GEOMETRY
LENGTH: 12.2 km (12.4 km)
AVERAGE STRIKE: N38°W±11°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Probable left lateral (sinistral)

GEOMORPHIC EXPRESSION: It forms a straight lineament almost 8 km long related to scarps and shutter ridges along the deeper valleys. The fault is shown as mostly discontinuous on the basis of its geomorphic expresión.

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

EC-30b, RÍo Cinto section

SECTION NUMBER: EC-30b

SECTION NAME: Río Cinto

SECTION GEOMETRY
LENGTH: 8.0 km (8.0 km)
AVERAGE STRIKE: N51°W±9°
AVERAGE DIP: Unknown
SENSE OF MOVEMENT: Left-lateral (sinistral)

GEOMORPHIC EXPRESSION: The fault controls the drainages of the Cinto and Tandacazo rivers (Eguez and Yepes, 1994).

RECURRENCE INTERVAL: Unknown

SLIP RATE: Unknown, probably <1 mm/yr

TIME OF MOST RECENT OF MOVEMENT: Quaternary (<1.6 Ma)

REFERENCES

Eguez, A., and Yepes, H., 1994, Estudio neotectónico y de peligro sísmico para el Proyecto Hidroeléctrico Toachi: INECEL (inédito), 63 p.

EC-31, Quito fault

FAULT NUMBER: EC-31

FAULT NAME: Quito
Comments: Named the Quito-Ilumbisí fault by Soulas and others (1991). The simpler name Quito fault is used here. These faults extend along the eastern margin of a high (uplifted) basin that the city of Quito is built on.

SYNOPSIS AND GEOLOGIC SETTING: These reverse faults limit and produce the elongated ridges that border the eastern side of the Pliocene-Quaternary Quito basin. These en echelon ridges are underlain by fluvial and pyroclastic deposits and form a broad flexure covered by deposits of the Cangahua formation (loess). This structure (plateau) has been described as a fold related to a blind thrust. Gravity-induced normal faults appear on the top and the flanks of the flexure (Soulas and others, 1991; Ego and others, 1995).

COMPILER, AFFILIATION, & DATE OF COMPILATION: A. Eguez, A. Alvarado, and H. Yepes; Escuela Politécnica Nacional, Departamento Geología and Instituto Geofísico; March 1997.

TYPE OF STUDIES: Photo interpretation and fieldwork.

FAULT GEOMETRY
LENGTH: 30.5 km (34.2 km)
AVERAGE STRIKE: N9°E±21°

NUMBER OF SECTIONS: 2
Comments: Sections defined by right step between two parallel strands (sections).

EC-31a, Northern section

SECTION NUMBER: EC-31a

SECTION NAME: Northern
Comments: Northern of two sections. South section is more eastward.

SECTION GEOMETRY
LENGTH: 17.5 km (18.5 km)
AVERAGE STRIKE: N4°E±22°
AVERAGE DIP: 60° to the west.
Comments: The dip was determined from a composite focal mechanism calculated by Bonilla and others (1992) and Guiller (personal communication to compilers).
SENSE OF MOVEMENT: Reverse, with dextral component.

GEOMORPHIC EXPRESSION: This fault section forms a broad asymmetric flexure with a steep eastern limb. The Quito Basin is separated from and about 400 m above the adjacent Interandean Valley (Cumbaya Basin) by the flexural ridge. Other morphological features include disturbed drainages. Scarps involving many landslides are located at the eastern limit of the Quito Basin.

RECURRENCE INTERVAL: 1.5-4.0 k.y.
Comments: Calculated from slip rate reported by Soulas and others (1991)

SLIP RATE: 0.2-1.0 mm/yr
Comments: Determined from offset of Quaternary terraces of the Monjas River (Soulas and others, 1991)

TIME OF MOST RECENT OF MOVEMENT: Holocene and post glacial (<15 ka)
Comments: Inferred from slip rate reported above.

EC-31b, Southern section

SECTION NUMBER: EC-31b

SECTION NAME: Southern
Comments: Southern of two sections. Northern section is more westward.

SECTION GEOMETRY
LENGTH: 15.0 km (15.7 km)
AVERAGE STRIKE: N16°E±19°
AVERAGE DIP: 60° to west.
Comments: The dip was determined from a composite focal mechanisms calculated by Bonilla and others (1992) and by Guiller (personal communication to compilers). This historic earthquake is thought to have been associated with this section of the Quito fault, although no historic surface deformation has been documented.
SENSE OF MOVEMENT: Reverse dextral

GEOMORPHIC EXPRESSION: This section forms a broad flexure with a s

Database and Map of Quaternary faults and folds of Ecuador and its offshore regions

By Arturo Eguez, Alexandra Alvarado, Hugo Yepes, Michael N. Machette, Carlos Costa and Richard L. Dart

Open-File Report 03-289

LIST OF TABLES

PREPARATION OF MAP AND DATABASE

EC-06, MACHE Lineament