Accession Number:

ADA169413

Title:

Body and Surface Wave Modeling of Observed Seismic Events.

Descriptive Note:

Semi-annual rept. no. 1, 14 Jan-13 Jul 85,

Corporate Author:

CALIFORNIA INST OF TECH PASADENA SEISMOLOGICAL LAB

Report Date:

1985-01-22

Pagination or Media Count:

51.0

Abstract:

This research covered two major topics modeling the effects of laterally heterogeneous source structure on Rayleigh waves, and modeling the effect of large horizontal gradients on body waves using a mixture of generalized ray theory and WKBJ or Disk rays. Results are presented for the modeling of fundamental Rayleigh waves from explosions where the source region geology differs from the propagation path using the representation theorem RT to couple finite element source regions calculations to model calculations at teleseismic distances. For the fundamental mode Rayleigh waves generated by explosions with constant moment, the amplitude of the wavetrain increases when the rigidity of the source material is decreased. Amplication factors of 6 were found when the source material was an order of magnitude less rigid than the surrounding medium. These amplitudes were not predicted by the Conversation of Lateral Energy Flux CLEF approximation. However, when the impedance contrast is gradational across the boundary the CLEF results agree more closely with the RT calculations. Techniques for calculating synthetics on structure models involving large horizontal gradients in velocity are presented. Recent models of earth structure suggest large horizontal gradients, especially in shear velocities. Changes in existing methods are required to construct synthetics for broadband signals in many situations, especially when energy can reach the receiver by up-going as well as down-going paths. This can be accomplished by allowing locally dipping structure and making modifications to generalized ray theory.

Subject Categories:

  • Seismology
  • Numerical Mathematics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE