A PRELIMINARY EARTHQUAKE HAZARD MAP FOR AFGHANISTAN

With funding from the U.S. Agency for International Development, the U.S. Geological Survey has prepared a series of probabilistic seismic hazard maps to aid in the ongoing reconstruction in Afghanistan. Our probabilistic methodology involved a complete hazard analysis for ~35,000 sites in the study area and accounted for the rates of earthquake activity from many potential seismic sources. We incorporated modeling uncertainty using logic trees for source and ground-motion parameters.

Producing the maps was challenging because of limited relevant geological and seismological data. The available data included a catalog of historical seismicity and poorly constrained slip rates for only a few of the many active faults. Much of the hazard is derived from a new catalog of instrumentally recorded earthquakes from 1964 to the present, with magnitudes ³4.5, and depths of £250 km. Our model includes four specific faults: the Chaman with a slip rate of 10 mm/yr, the Central Badakhshan with a slip rate of 12 mm/yr, the Darvaz with a slip rate of 7 mm/yr, and the Hari Rud with a slip rate of 2 mm/yr. For these faults and for shallow seismicity £50 km deep, we used published ground-motion estimates from analogous tectonically active regions of western North America, Europe, and the Middle East. For deeper seismicity, we used published ground-motion estimates derived from data in subduction-zone environments.

Our analysis shows that seismic hazard is high in northeastern Afghanistan and much lower in the western half of the country. Hazard levels in Kabul, with contributions from the regional seismicity and the nearby Chaman fault, are roughly similar to the hazard in seismically active parts of the Intermountain West of the United States. We estimate that Kabul has a 2-percent chance in 50 years of exceeding a peak ground acceleration of 50 percent g, and a 10-percent chance in 50 years of exceeding a peak ground acceleration of 27 percent g. Hazard increases northeast of Kabul through the highly seismic Hindu Kush, especially at sites near the Central Badakhshan and Darvaz faults, where hazard levels approach those found in some seismically active parts of California. Our hazard analysis is available in USGS Open-File Report 2007-1137 (http://pubs.usgs.gov/of/2007/1137/).