On seismological moments and magnitudes
B. A. Bolt
1991, Earthquakes & Volcanoes (USGS) (22) 111-112
My approach to seismology over the years has always been from the point of view of applied mathematics, as exemplified broadly by the work of the late Sir Harold Jeffreys and Professor K. E. Bullen. Both stresses the development of mathematics in the context of physical systems and of modeling,...
The southeastern Illinois earthquake of 10 June 1987: The later aftershocks
C.J. Langer, G. A. Bollinger
1991, Bulletin of the Seismological Society of America (81) 423-445
The 10 June 1987 southeastern Illinois earthquake (mbLg = 5.2) was the seventh in a series of moderate magnitude (≧ 4.5) MMI VII shocks to occur in the Wabash Valley seismic zone of southeastern Illinois and southwestern Indiana since 1891. Located about 200 km east of St. Louis, Missouri, the...
Jurassic normal and strike-slip faults at Crater Island, northwestern Utah
D. M. Miller, R.W. Allmendinger
1991, Geological Society of America Bulletin (103) 1239-1251
At Crater Island, northern Silver Island Mountains, northwestern Utah, an unbroken Tertiary fault block within the Basin and Range province exhibits Jurassic or older structures that are virtually unmodified by subsequent tectonism, providing an opportunity to examine the tectonics of the Jurassic back arc of the Cordillera. Widespread high-angle faults,...
Geohydrology of the High Plains aquifer system, Cheyenne urban area, Wyoming
Maurice E. Cooley, Marvin A. Crist
1991, Water-Resources Investigations Report 92-4047
The Cheyenne area is on broad tablelands that form part of the High Plains aquifer. Surficial deposits, along with the Ogallala Formation and the White River Group, are included in the High Plains aquifer in the study area, and both unconfined and confined ground-water conditions exist within 100 feet of...
Brine evolution and mineral deposition in hydrologically open evaporite basins
W. E. Sanford, W.W. Wood
1991, American Journal of Science (291) 687-710
A lumped-parameter, solute mass-balance model is developed to define the role of water outflow from a well-mixed basin. A mass-balance model is analyzed with a geochemical model designed for waters with high ionic strengths. Two typical waters, seawater and a Na-HCO3 ground water, are analyzed to illustrate the control that...
Multicycle slip distribution along a laboratory fault
Chi-Yu King
1991, Journal of Geophysical Research (96)
Slip distribution along a laboratory fault, which consists of eight spring-connected blocks that are elastically driven to slide on a frictional surface, has been examined for a “long” sequence of slip events to test the applicability of some conceptual models proposed recently in the literature. The...
Stress magnitudes in the crust: constraints from stress orientation and relative magnitude data
M.L. Zoback, M. Magee
1991, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences (337) 181-194
The World Stress Map Project is a global cooperative effort to compile and interpret data on the orientation and relative magnitudes of the contemporary in situ tectonic stress field in the Earth's lithosphere. The intraplate stress field in both the oceans and continents is largely compressional with one or both...
Mineral remains of early life on Earth? On Mars?
E. Iberall-Robbins, A. S. Iberall
1991, Geomicrobiology Journal (9) 51-66
The oldest sedimentary rocks on Earth, the 3.8‐Ga Isua Iron‐Formation in southwestern Greenland, are metamorphosed past the point where organic‐walled fossils would remain. Acid residues and thin sections of these rocks reveal ferric microstructures that have filamentous, hollow rod, and spherical shapes not characteristic of crystalline minerals. Instead, they resemble...
Estimates of velocity structure and source depth using multiple P waves from aftershocks of the 1987 Elmore Ranch and Superstition Hills, California, earthquakes
J. Mori
1991, Bulletin of the Seismological Society of America (81) 508-523
Event record sections, which are constructed by plotting seismograms from many closely spaced earthquakes recorded on a few stations, show multiple free-surface reflections (PP, PPP, PPPP) of the P wave in the Imperial Valley, California. The relative timing of these arrivals is used to estimate the strength of the P-wave...
Thermodynamic assessment of hydrothermal alkali feldspar-mica-aluminosilicate equilibria
D.A. Sverjensky, J.J. Hemley, W. M. d’Angelo
1991, Geochimica et Cosmochimica Acta (55) 989-1004
The thermodynamic properties of minerals retrieved from consideration of solid-solid and dehydration equilibria with calorimetric reference values, and those of aqueous species derived from studies of electrolytes, are not consistent with experimentally measured high-temperature solubilities in the systems K2O- and Na2O-Al2O3-SiO2-H2O-HCl (e.g., K-fs — Ms — Qtz — K+ — H+)....
Exploration drilling and reservoir model of the Platanares geothermal system, Honduras, Central America
F. Goff, S.J. Goff, S. Kelkar, L. Shevenell, A.H. Truesdell, J. Musgrave, H. Rufenacht, W. Flores
1991, Journal of Volcanology and Geothermal Research (45) 101-123
Results of drilling, logging, and testing of three exploration core holes, combined with results of geologic and hydrogeochemical investigations, have been used to present a reservoir model of the Platanares geothermal system, Honduras. Geothermal fluids circulate at depths ??? 1.5 km in a region of active tectonism devoid of Quaternary...
Metasomatic oxidation of upper mantle periodotite
A. V. McGuire, M.D. Dyar, J. E. Nielson
1991, Contributions to Mineralogy and Petrology (109) 252-264
Examination of Fe3+ in metasomatized spinel peridotite xenoliths reveals new information about metasomatic redox processes. Composite xenoliths from Dish Hill, California possess remnants of magmatic dikes which were the sources of the silicate fluids responsible for metasomatism of the peridotite part of the same xenoliths. Mo??ssbauer spectra of mineral separates...
Moment-tensor solutions estimated using optimal filter theory: global seismicity, 1988-1989
S.A. Sipkin, R.E. Needham
1991, Physics of the Earth and Planetary Interiors (67) 221-230
Moment-tensor solutions, estimated using optimal filter theory, are listed for 201 moderate-to-large earthquakes occurring from 1988 to 1989. ?? 1991....
Pre-exploitation state of the Ahuachapán geothermal field, El Salvador
Z. Aunzo, C. Laky, B. Steingrimsson, G.S. Bodvarsson, M.J. Lippmann, A.H. Truesdell, C. Escobar, A. Quintanilla, G. Cuellar
1991, Geothermics (20) 1-22
The lithology and structural features of the Ahuachapán geothermal area and their impact on the movement of cold and hot fluids within the system are described, as well as the development and evaluation of the natural state model of the field. Four major lithologic units are present in Ahuachapán and...
Re - Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle
R.J. Walker, L.M. Echeverria, S.B. Shirey, M.F. Horan
1991, Contributions to Mineralogy and Petrology (107) 150-162
The Re - Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155??43 Ma. Subsequent episodes of volcanism produced basalts at 88.1??3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important...
Development of a land-cover characteristics database for the conterminous U.S.
Thomas R. Loveland, J.W. Merchant, D.O. Ohlen, Jesslyn F. Brown
1991, Photogrammetric Engineering and Remote Sensing (57) 1453-1463
Information regarding the characteristics and spatial distribution of the Earth's land cover is critical to global environmental research. A prototype land-cover database for the conterminous United States designed for use in a variety of global modelling, monitoring, mapping, and analytical endeavors has been created. The resultant database contains multiple layers,...
Calibration of a texture-based model of a ground-water flow system, western San Joaquin Valley, California
Steven P. Phillips, Kenneth Belitz
1991, Ground Water (29) 702-715
The occurrence of selenium in agricultural drain water from the western San Joaquin Valley, California, has focused concern on the semiconfined ground-water flow system, which is underlain by the Corcoran Clay Member of the Tulare Formation. A two-step procedure is used to calibrate a preliminary model of the system for...
Densities of liquids and vapors in boiling NaCl-H2O solutions: a PVTx summary from 300° to 500°C
James L. Bischoff
1991, American Journal of Science (291) 309-338
Experimental data for densities of liquids and vapors on the two-phase surface of the system NaCl-H2O were compiled and evaluated to provide a complete summary between 300° and 500°C. The results are added to a previously published PTx summary compiled in the same manner to provide a PVTx summary of...
Numerical assessment of a landfill compliance limit
Bruce R. Hensel, Donald A. Keefer, Robert A. Griffin, Richard Berg
1991, Groundwater (29) 218-224
The PLASM and Random Walk ground-water flow and contaminant transport models were used to assess the potential impact of various proposed regulatory compliance distances on landfill siting. Contaminant transport modeling was performed for 16 generalized geological sequences representative of hydrogeological conditions over an estimated 90...
Sensitivity analysis of a ground-water-flow model
Lynn J. Torak
Lennon Gerard P.Rouhani Shahrokh, editor(s)
1991, Conference Paper, Symposium on Ground Water
A sensitivity analysis was performed on 18 hydrological factors affecting steady-state groundwater flow in the Upper Floridan aquifer near Albany, southwestern Georgia. Computations were based on a calibrated, two-dimensional, finite-element digital model of the stream-aquifer system and the corresponding data inputs. Flow-system sensitivity was analyzed by computing water-level residuals obtained...
Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon
T.Z.L. Tourrette, D.S. Burnett, C. R. Bacon
1991, Geochimica et Cosmochimica Acta (55) 457-469
Crystal-liquid partitioning in Fe-Ti oxides and zircon was studied in partially melted granodiorite blocks ejected during the climactic eruption of Mt. Mazama (Crater Lake), Oregon. The blocks, which contain up to 33% rhyolite glass (75 wt% SiO2), are interpreted to be portions of the magma chamber walls that were torn...
Capture zones for simple aquifers
Carl D. McElwee
1991, Ground Water (29) 587-590
Abstract. The protection and cleanup of aquifers is a matter of high priority for all states and the federal government. One concept that is receiving increased attention is that of wellhead protection. Capture zones showing the area influenced by a well within a certain time are...
Geochemistry of lavas from Taal volcano, southwestern Luzon, Philippines: evidence for multiple magma supply systems and mantle source heterogeneity
Asta Mikijus, M.F.J. Flower, J.P.P. Huijsmans, S.B. Mukasa, P. Castillo
1991, Journal of Petrology (32) 593-627
Taal Volcano is a highly active center in the southwest Luzon volcanic field. Recent eruptions are confined to Volcano Island, a plexus of cinder cones and tuff rings surrounding a central crater, occupying (and post-dating) a massive volcano-tectonic depression resulting from multiple phases of collapse. Taal lava series can...
A lead isotopic study of the Stillwater Complex, Montana: constraints on crustal contamination and source regions
J. L. Wooden, G.K. Czamanske, M. L. Zientek
1991, Contributions to Mineralogy and Petrology (107) 80-93
Analyses of the Pb isotopic compositions of plagioclase from 23 samples covering the stratigraphic thickness of the Stillwater Complex indicate a narrow range of apparent initial isotopic compositions (206Pb/ 204Pb=13.95; 207Pb/204Pb=14.95-15.01; 208Pb/204Pb=33.6). The uniformity of our data is in contrast to, but not necessarily contradictory to, other recent investigations which...
Petrology of lower crustal and upper mantle xenoliths from the Cima Volcanic Field, California
H. G. Wilshire, A. V. McGuire, J.S. Noller, B. D. Turrin
1991, Journal of Petrology (32) 169-200
Basaltic rocks of the Cima volcanic field in the southern Basin and Range province contain abundant gabbro, pyroxenite, and peridotite xenoliths. Composite xenoliths containing two or more rock types show that upper-mantle spinel peridotite was enriched by multiple dike intrusions in at least three episodes; the mantle was further...
