Seismic velocity structure and event relocation in Kazakhstan from secondary P phases. (Reannouncement with new availability information)
Three-component seismic data from a set of presumed explosions recorded by stations at Bayanaul and karkaralinsk in Kazakhstan were analyzed in order to model the crustal structure of the region and to examine the use of the arrival times of secondary P phases, primarily PmP, in regional event location. Polarization analysis aided in the identification of the secondary phases. Low-pass filtered data (4-Hz corner) from the first 5 to 10 sec of 13 presumed explosions were modeled with the reflectivity method. The two chemical explosions in 1987 provided a check on accuracy, as their locations and origin times are accurately known. A good fit to the arrival times and amplitudes in the first 5 sec of the P wave (Pn, Pg, and PmP) was obtained in the epicentral distance range of 100 to 300 km. Beyond 300 km, the simple layered model was not adequate to model the PmP arrival. The crustal P-wave velocity model were derived has an upper crustal velocity increasing fairly rapidly from 4.5 km/sec near the surface to 6.5 km/sec at 15-km depth, then increasing more slowly to 7.05 km/ sec at 50-km depth. The observed difference in the arrival times of the phases Pg, PmP, and Pn in the range between 100- and 250-km distance required a relatively sharp transition at the crust mantle boundary. The model is generally similar to previous estimates of P velocity structure in the region, though with a gentler gradient in the upper crust and a steeper gradient in the lower crust.
- Research Organization:
- Wisconsin Univ., Madison, WI (United States). Dept. of Geology and Geophysics
- OSTI ID:
- 200114
- Report Number(s):
- AD-A--261708/2/XAB; CNN: Contract F19628-90-K-0047
- Country of Publication:
- United States
- Language:
- English
Similar Records
Tomography and Methods of Travel-Time Calculation for Regional Seismic Location
DEPTH OF FOCUS DISCRIMINATION BY CRUSTAL PHASES FOR NTS NUCLEAR EXPLOSIONS. Research Paper P-12