Use of Source-Region-Station Time Corrections at NTS for Depth Estimation
TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA ANALYSIS CENTER
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Travel time residuals may be obtained from a least-squares location program which is run with the depth constrained to the known true value. When these residuals are used as travel-time corrections in the same program run depth-free, nearby events are located with smaller errors in depth. An elaboration of this technique has been denoted the SRST Source-Region-Station- Time technique by K. Veith. In this study the technique is applied to Nevada Test Site NTS explosions. The mean estimated depth is changed from approximately 50 km to approximately 0 km with standard deviations of 30 km for a well-distributed 5-station network, and 20 km for a 9-station network. It is pointed out that the technique can be in serious error is deep earthquakes are used to determine residuals for shallow explosions in a source area where the earth structure between the earthquake and surface is different from that implied by the travel-time table used. It is also shown that there is no evidence for change of travel-time residuals with time for arrivals from NTS at RKON, NPNT, BUL, ane PRE. There is, however, evidence that significant changes in residuals are correlated with location at Pahute Mesa and that the changes may be due to interactions with a deep volcanic plug under Pahute Mesa.