The Effects of Structure and Source Complexity on Waveforms: Crustal Structure of Tibet and the Recovery of Complex Seismic Sources
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 km/s 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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 07, 1989
- Accession Number
- ADA218202
Entities
People
- Terry C. Wallace
Organizations
- University of Arizona