Open-File Report 2007–1255
U.S. GEOLOGICAL SURVEY
Open-File Report 2007–1255
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Our goal is to provide hazards information in the form of concrete products needed to support communities in the decision-making process. The research needs for urban-hazard products are highly interdependent, as table 1 illustrates, highlighting the need for cross-cutting research products and interactive analytical tools designed for decision makers’ use. Our first-year and out-year goals incorporate these needs and are influenced by the two-way communication that continues to take place among scientists and between scientists and community decision makers. The working groups will have solidified during the first year, and we list them here to categorize the project activities. All four areas will require significant integration of research across scientific disciplines and with community partners.
Scenario development. The first round of strategic planning workshops with our user community highlighted a high-priority need for planning scenarios that can be used to devise hazard-response training exercises for their organizations. The community wants hazard information provided in a form that is accessible to and understandable by decision makers. During the first year, a scenario will be developed that describes the pre-event and post-event risks and probabilities associated with a southern San Andreas earthquake that triggers landslides (including one underwater) and a dam failure. The scenario will incorporate the general consequences associated with the potential impacts of a strong earthquake (for example, expected shaking intensity, secondary effects such as liquefaction and subsequent lateral spreading, and variations in site conditions based on soil type), landslide (for example, probability of initiation made on the basis of shaking intensity, rock type, slope steepness, and soil moisture conditions), and potential tsunami (probability based on landslide displacement characteristics and historical activity, impact on coastal communities from run-up height and inundation estimates). The potential area that can be inundated by flood waters released by a dam failure will be identified. Moreover, the scenario will demonstrate the effect on infrastructure such as highways, airports, railroads, marine facilities, communications, water supply and waste disposal, electrical power, natural gas, and petroleum fuels. A key element of the scenario will be software that can illustrate the levels of damage on the basis of structure types (for example, unreinforced masonry compared with steel moment frame), age of structure, and hazard-retrofitting history of structure. A related study, begun in 2006, will focus on the effect of an earthquake on water supplies and on how to use ground water to compensate.
Community interface. We will start a training program that will serve as a continuing process for helping communities use our products. The program will expand in FY 2008 to support the use of the new products that will be generated by this project. The information exchange will take place during scheduled workshops that will focus on developing effective mechanisms of communication between the decision makers and scientists before, during, and after hazard events. Two-way information exchange that guides the development of planning scenario content for use by the decision makers will take place during workshops and staff exchange programs. We aim to provide accurate and complete information to support those entities that provide outreach and education to the public and to promote interaction between users and scientific partners.
Information management. A large quantity of data has been accumulated for southern California for different purposes, in different formats, and for different geographical regions. We will be more efficient if we make use of all the existing pieces of relevant data. However, work is necessary to determine what data exist and how they may be useful. During the first year, we will focus on inventorying the data resources, determining both the needs and capabilities of researchers and partners, and developing a management plan for the most cost-effective information management strategy.
Risk modeling. We will initiate a risk-assessment methodology of multiple natural hazards in southern California that incorporates conditional (triggered secondary) hazard probabilities over a range of hazard magnitudes and severities. Probabilities of changes in land-cover, land-use, and demographics will be incorporated into model alternative futures for the communities. The work will involve the consolidation of hypotheses and empirical findings from the economic literature on risk reduction into a single decision framework. A key product will be the development of a tool to reveal decision-maker preferences regarding the key elements of the decision framework.
Southern San Andreas Fault. The southern San Andreas Fault is recognized as southern California’s most likely source of future great earthquakes, but the past history of great earthquakes and the rate at which strain is accumulating towards the next big earthquake is poorly understood. We will study the southern San Andreas Fault to improve the accuracy of hazard assessments of the region and to determine the likelihood of another large earthquake on this fault segment.
Tsunami source. We will move toward a probabilistic assessment of tsunami inundation in southern California by developing an improved understanding of local tsunami sources and the likely time history of their activity. We will re-examine all available geophysical and core data to improve upon our characterizations of tsunami sources and obtain better chronologic control on available core samples near faults and large landslides to better define history of activity and recurrence intervals.
Microzonation. Loose soils and basin deposits locally amplify seismic shaking and can be responsible for substantial damage. The fastest population growth in southern California is occurring in basins near the San Andreas Fault, including the San Bernardino, Coachella, and Antelope Valleys. We will compile existing data on these basins to develop a preliminary shaking amplification model and determine which data are needed to accurately quantify this risk.
Fuel treatments on stability. Soil erosion after large wildfires degrades both the ecologic and urban environments. We will evaluate how vegetation age and landscape fuels affect the rates of erosion following fires, using vegetation age, sediment, and remote imaging data.
Vegetation-type conversions. The shrublands of southern California have undergone significant change of vegetation type in the last century as human activity has brought exotic species to the ecosystems. We will begin the evaluation of the invasive species-fire cycle to determine what role conversion of ecosystems is playing in fire frequency.
Post-fire debris-flow susceptibility. The incidence of debris flows after fires is controlled by the topography and geology of the slope, the severity of the burning, and the intensity and duration of rainfall. Models to predict post-fire debris-flow probabilities, magnitudes, and potential inundation areas using measures of basin shape and materials, burn severity, and storm data will be modified and tested for the southern California environment.
Post-fire erosion. The southern California ecosystem is home to the greatest concentration of endangered species in the Nation. We will develop models and methods to map post-fire physical processes and effects on rare and endangered aquatic populations.
Debris-flow warning system. The results of the southern California models will be used to develop a flash-flood and debris-flow early warning system for release by NOAA for recently burned basins. The warning system will compare rainfall forecasts and rain-gage data with rainfall threshold conditions.
Debris-flow inundation. Identify areas susceptible to debris-flow inundation through a combination of empirical and modeling approaches to (1) identify likely source areas for debris-flow initiation, (2) estimate likely debris-flow volumes and peak discharges, and (3) determine areas likely to be inundated by debris flows. Debris-flow source-area identification will be a combined mapping and Geographic Information System (GIS) endeavor. Mapping of recent debris flows by field and remote sensing techniques will provide an empirical data base of debris-flow initiation locations that can be analyzed within a GIS to assess likely controlling factors such as topography (including slope, hill-slope curvature, and aspect), geology, soils, land-use, and recent disturbance history (such as fire).
Gaging (streams, rain). Install new stream and rain gages in southern California to improve flood and debris-flow forecasting, and real-time monitoring and warning capabilities. The gage locations are being selected with input from local water agencies and the National Weather Service to fill in gaps in the existing ALERT network. The gages will be constructed, instrumented, and operated to provide real-time streamflow information on the web during FY 2007 for access to all interested users.
Flood frequency analysis. Winter storms can produce significant flood runoff and debris flows from basins throughout Southern California. Distinguishing flood flows from debris flows is critical to the proper assessment of flood risk, but there is no USGS database for debris flows. A database for compiling and storing debris-flow data for USGS gaged sites, similar to the Peak Flow File for flood data, will be developed. Assessing flood risk also requires information about magnitude and probability of occurrence (frequency) of annual peak flood discharges. Long-term flood-discharge data are available for the analysis at more than 100 USGS stream gages in southern California, many of which provide flow information on a near real-time basis via the web. Flood-frequency characteristics will be revised and prepared for publication during FY 2007.
Coastal erosion. Severe winter storms have eroded seacoasts, leading to major economic losses. We will develop tools to assess coastal vulnerability to severe storm impact based on elevation and morphology data.
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