Analyses and Simulation of 3D Scattering Due to Heterogeneous Crustal Structure and Surface Topography on Regional Phases, Magnitude Discrimination
Abstract
The main purpose of this study is the understanding of scattering and its effects through step-by-step numerical experiments and waveform modeling, with the goal of providing useful insights into ongoing research for the development of simple empirical models of scattering that can be used in reducing the scatter in measures of Lg and coda wave magnitude and for discrimination purposes as well. We are performing anelastic 3D finite-difference simulations of wave propagation in highly heterogeneous media for a range of source depths, receiver distances and source types. In the first stage of our study we investigated the effect of small-scale crustal heterogeneities on wave propagation scattering. During the second stage we investigated the effect of surface topography combined with crustal heterogeneities on wave propagation scattering. In our simulations of regional wave propagation we used a finite difference computer program using our computer cluster. The seismograms were calculated at up to 3.5 Hz for regional distances of up to 300 km. The topography elevation was simulated using correlated random variations along the free surface. Our simulations show that the surface topography increases the wave-path scattering effects. The combined effects of crustal heterogeneities and surface topography produce Lg, P, and S coda waves with significant energy even for explosion sources. The energy of Lg coda waves depends on the source depth. P/Lg ratios estimated at different frequencies indicate that this ratio could be a good discriminant between explosions and earthquakes when calculated at high frequencies. The wave-path scattering effects were also investigated by simulating observed high frequency source directivity effects, as well as fault zone wave trapping in highly fractured conditions from aftershocks of the Big Bear earthquake sequence.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 2008
- Accession Number
- ADA487729
Entities
People
- Arban Pitarka
- Don V. Helmberger
- Sidao Ni