Seismic-event locations using multiple phases. Final report, March-November 1985

Technical Report · Sat Nov 30 04:00:00 EST 1985

OSTI ID:6533157

Chang, A C

This work evaluates the utility of a travel/travel Covariance Matrix Method (COVMTX) for the improvement of the location of seismic events at regional distances using both Pn and Pg arrival times. Correlations between Pn and Pg travel-time residuals are determined for the data set. The correlation of Pn and Pg times, rho/sub PnPg/ for signals received at the same station from the same event was found to be very poor, less than 0.3 in all computations. The Covariance Matrix Method did not improve the results, possibly because the systematic bias due to the clustering of stations is small for the particular network of stations used in the relocation. Nevertheless, the method is still valuable because we must weight each signal differently, especially when multiple phases are used. The Simultaneous Inversion Method often resulted in erroneous depth estimates because the inversion for the depth dependent terms a sub Pn and a/sub Pg/ in the linear travel time formula t = a + b delta may end up with some unacceptable values. By restricting the inversion for the a coefficients, the relocation resulted in the best results. This restriction is similar to the Successive Determinations Method devised by Chang et al. (1981), because it only improves the velocities or the b coefficients. This result suggests that a successive determinations approach may be very useful in locations using later phases, where large local variations in travel times are noted but are unpredictable prior to the location.

• Research Organization: Teledyne Geotech, Alexandria, VA (USA). Alexandria Labs.
• OSTI ID: 6533157
• Report Number(s): AD-A-177778/8/XAB; TGAL-85-10
• Country of Publication: United States
• Language: English

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