USGS identifier

Science Goals

Goal 1--Conduct geologic hazard assessments for mitigation planning

Natural geologic hazards, such as earthquakes, landslides, volcanic eruptions, coastal erosion, and floods, result in considerable human suffering and billions of dollars in losses in the United States every year. Although the occurrence of these hazards generally cannot be prevented, the resulting losses to life and property can be significantly diminished through disaster mitigation based on scientific assessments of potential damage. These assessments indicate where and how often natural geologic disasters might occur, as well as provide information on their size and the effects these disasters could have on infrastructure.

The USGS is the acknowledged national leader in developing geologic-hazard assessment methods and products and will continue to strengthen and expand this role. The GD provides two essential types of hazard assessments. Deterministic assessments describe the effects that a particular disaster may have on a region. Probabilistic assessments describe the likelihood of a specific type of hazard and its geologic effects. For example, in a deterministic assessment, scientists could calculate the geologic effects of a magnitude 7.5 earthquake on a specific segment of the San Andreas fault, largely on the basis of observations of damage from past earthquakes. In contrast, a probabilistic assessment could portray the likelihood of earthquake-induced ground motion exceeding a particular threshold, due to an earthquake or any combination of earthquakes, in a given region over a set time period. This information is being used to help define national building codes, appropriate insurance rates, and local zoning regulations (see Highlight 5). GD hazard assessments will focus primarily at the national and regional scale, and will be supplemented by detailed local investigations in carefully selected high-risk areas. These local investigations are intended to lead to fundamental advances in hazard-assessment methodology and will be conducted in close collaboration with State and local agencies. The utility and credibility of geologic hazard assessments are based on the continuing long-term scientific research carried out by the GD, particularly studies of factors controlling the geographic distribution, magnitude, timing, and geological consequences of hazardous events. The cost-effectiveness of this integrated research and assessment effort has been demonstrated many times and will continue to provide similar benefits to the Nation.


Regional- and national-scale probabilistic hazard maps and interactive data bases.
These maps and data bases will be prepared for hazards such as earthquakes, volcanoes, landslides, coastal erosion, and floods (the last in collaboration with the WRD). For all probabilistic hazard maps, the likelihood of future hazardous events must be determined first. GD scientists make this determination on the basis of a chronology of past events and an understanding of physical causes for variability in event recurrence. Once the probability of such events is established, the resultant harmful effects can be quantified, as long as a variety of important source, site-response and other parameters can be estimated (see Highlight 6). Future generations of probabilistic seismic hazard maps should incorporate more complete scientific information on fault rupture characteristics, the materials through which seismic waves are transmitted, the response of surface deposits to shaking, the time elapsed since the last major seismic event, and possible stress transfer effects following large earthquakes.

Deterministic scenarios to aid in local and regional planning efforts.
Even when the probability of a given event is low, deterministic modeling allows land-use managers, urban and infrastructure planners, and emergency-preparedness groups to envision and plan for the range of potential consequences of natural catastrophes. For example, landslides and mudflows from Pacific Northwest volcanoes pose threats not only to local communities but also to transportation networks and power transmission lines that provide electricity to regional urban centers. Government agencies, private industry, and the public must be made aware of the full consequences of hazardous geologic events and ongoing geologic processes in order to plan appropriately.

Multihazard assessments for selected urban areas.
The GD will prepare these assessments in cooperation with State and local agencies. Individual hazardous events can have a range of spin-off effects that cause significant damage. For example, wildfires remove vegetation from entire hill slopes, creating the potential for subsequent landslides and floods. Earthquakes can cause liquefaction of soil, floods from collapsed dams, and fires (such as the one that devastated San Francisco in 1906). It is important to incorporate multiple, interrelated hazards in hazards assessments and models, particularly for major metropolitan regions.

Vulnerability maps and interactive data bases for geologic hazards.
These maps and data bases will incorporate information on the tendency of earth materials to fail or be remobilized by natural and manmade processes. For example, a vulnerability map showing areas underlain by artificial fill and other water-bearing sediments can help identify buildings and critical facilities at risk due to high levels of shaking or ground failure during earthquakes. Maps of playas and dunes will show sources of airborne sediment that are likely to be activated during dust and sand storms. Maps depicting the distribution of soils and poorly cemented sediments can be used to predict which areas are most susceptible to erosion during flash floods and coastal storms. In addition to providing data to be incorporated into the first three products, vulnerability maps and interactive data bases are useful in and of themselves for informing local planning agencies and the public about the types of human activities that may increase vulnerability to certain kinds of hazards.

Strategic Actions

Conduct detailed geological and geophysical field investigations.
These investigations will support probabilistic hazard mapping, deterministic scenarios, multihazard assessments, and vulnerability mapping in critical, high-risk (mostly urban) areas. This work, to be conducted in cooperation with USGS and non-USGS partners, will involve surficial and bedrock geologic mapping, surface-based geophysical imaging, shallow geotechnical studies, geomorphic analysis, and other investigations.

Document the recent geologic history of major hazardous events in the United States in unified data bases.
A chronology of past events is a critical ingredient in most probabilistic approaches to hazard assessment. These nationwide data bases will include the slip history of all faults with surface ruptures during the Holocene (the past 10,000 years) and selected faults with surface ruptures during the Quaternary (the past 1.8 million years). The data bases will also include the Quaternary eruption and debris-flow history for all active U.S. volcanoes and the history of major Holocene floods and landslides. Such work involves a mixture of geologic mapping, stratigraphy, Quaternary geochronology, and other investigations and will be undertaken in cooperation with non-USGS partners.

Investigate factors controlling the geographic distribution, magnitude, and timing of hazardous geologic events.
As the physical processes that lead to natural disasters and control their magnitude are more fully comprehended, we can better quantify potential effects and predict and mitigate damage as the disaster occurs (see Goal 2). Also, some types of hazardous events occur independently of one another, whereas other types of events (such as earthquakes) may be linked through a variety of physical processes affecting when and where they will occur. Understanding the physical basis for event frequency and clustering is critical to any quantitative hazard assessment.

Determine the physical processes responsible for variations in local site response to natural hazards.
The consequences of a hazardous event depend not only on its intrinsic magnitude, but also on the characteristics of the affected areas, such as topography, rock and soil properties, and sedimentary basin geometry. The GD will develop easily measured proxies that can be substituted for parameters that are difficult to determine directly.

Develop and use consistent methods for local-, regional-, and national-scale hazard assessments for each type of hazard.
In addition, whenever possible, use similar hazard-assessment methods for different types of hazards. For example, techniques comparable to those now being used to calculate probabilities for earthquakes should be used to determine probabilities for floods and volcanic debris flows.

<----- Back to Contents || Back to Working with Others || Continue to Goal 2 ----->

This page is <>
Maintained by L. McElroy
Last updated 04.10.98