Path Calibration, Source Estimation and Regional Discrimination for the Middle East: Application to the Hindu-Kush Region.
Scientific rept. no. 1,
WOODWARD-CLYDE FEDERAL SERVICES PASADENA CA
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We have analyzed observations of earthquakes occurring in the Hindu-Kush region to establish a basis for location and discrimination using the new broadband station NIL, a GSETT-3 beta station, which is located near the site of the GSETT-3 alpha array PKAR in Pakistan. Preliminary analyses of the regional data at NIL in terms of energy ratios the integrated energy in the short-period Pn1 wavetrain, divided by the intermediate-period, three component, surface wave integrated energy produces plots not unlike those produced by a similar analysis of TERRAscope data for the southwestern U.S.. NTS explosions consistently plot higher than regional earthquakes in the latter population, Woods and Helmberger 1996. In the NIL earthquake population, there are observed events with high ratios which look like explosions but appear to be deep events where the surface waves have become weak relative to the body waves. The identical problem occurs for the mbMs discriminants for events in this region. Thus, the ability to determine the source depth becomes crucial in this region as a complimentary method to infer the source type. To calibrate the regional paths we selected 5 crustal and 5 sub-crustal events 5.5 Mw 4 to study in detail both teleseismically and regionally. Most of these local events were recorded by the temporary local arrays in Pakistan PAKN and in Kyrgyzstan KNET and by the IDC network of far-regional teleseismic stations.