The San Mateo County California Gis Project for Predicting the Consequences of Hazardous Geologic Processes

Abstract

Listen

Translate article

San Mateo County, California adjoining San Francisco has several hazardous geologic processes, including movement of the San Andreas fault and associated ground failures, landsliding, flooding, and coastal erosion. In the early 1970’s, county planners requested help from the U.S. Geological Survey in determining the location and severity of the most hazardous processes, and in preparing maps that would help them deal with the problems. Maps were prepared showing the location of fault zones and the most recently active fault traces, areas subject to flooding, and an inventory of past and recently active landslides. Geographic Information Systems (GIS) techniques were used to make a map of landslide susceptibility, but the analysis was done by hand.San Mateo County used these hazard maps to enact ordinances that limit the density of development permitted in geologically hazardous areas to as little as one dwelling unit per 16 hectares, and that require geologic reports and review by the County Geologist before any development is permitted. During the past two decades, these ordinances have been expanded in area and strengthened in application.The availability of this geologic-hazard data base, the innovative use of this information by the County, and the development of computer systems capable of manipulating large data sets and preparing color-separation negatives quickly, inexpensively, and with correct registration prompted a small group of U.S. Geological Survey scientists, engineers, cartographers, geographers, and computer specialists to consider a new set of hazard maps using computer-based GIS technology. Several new maps were prepared including slope and shaded relief maps prepared from a Digital Elevation Model; a map showing the direction and amount of bedding dip; a map showing the seismic-shaking intensities in a repeat of the 1906 San Francisco earthquake; maps showing cumulative damage potential to wood-frame, tilt-up concrete and steel buildings from earthquake ground shaking; a map showing where earthquake-triggered landslides will impact the county during a repeat of the 1906 earthquake; maps showing debris-flow probability; and a map of liquefaction susceptibility. These maps have been used by the county for general planning, to evaluate environmental impact reports, for the design of public facilities, for water supply and quality, and for land capability.KeywordsDebris FlowGeographic Information SystemLandslide SusceptibilityGeological Survey Open File ReportLiquefaction SusceptibilityThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.