Accession Number:

ADA218202

Title:

The Effects of Structure and Source Complexity on Waveforms: Crustal Structure of Tibet and the Recovery of Complex Seismic Sources

Descriptive Note:

Final rept. May 1987-May 1989

Corporate Author:

ARIZONA UNIV TUCSON DEPT OF GEOSCIENCES

Personal Author(s):

Report Date:

1989-09-07

Pagination or Media Count:

198.0

Abstract:

In an attempt to better understand the effects of both source and path on regional distance waveforms, we investigated the crustal structure of Eurasia and developed an algorithm for investigating complex seismic sources. Part I is a study based on the inversion of 130 regional distance waveforms for average crustal thickness and upper mantle Pn velocity beneath Tibet. Results indicate an increase in Pn velocity, coincident with the increase in crustal thickness, of about 0.2 kms beneath the Plateau. Impulsive Pn arrivals from paths that cross the Tibetan Plateau can be modeled with a positive upper mantle gradient, indicating an upper mantle lid approximately 100 km thick beneath southern Tibet. This shield-like structure has important consequences for the propagation of regional phases Pg, Pn and Sn. Part II discusses an algorithm for time dependent moment tensor TDMT inversion. The algorithm was developed to investigate complex seismic sources, such as multiple earthquakes and, ultimately, explosions with tectonic release contamination. The TDMT inversion algorithm was tested with 3 synthetic data examples with varying degrees of complexity. It was also tested on the long-period body waves for 3 earthquakes the 1982 Yemen, the 1971 San Fernando, and the 1952 Kern County earthquakes. Preliminary modeling in the nearfield of nuclear explosions yielded mixed results.

Subject Categories:

  • Seismology

Distribution Statement:

APPROVED FOR PUBLIC RELEASE