A Reciprocity Method for Multiple Source Simulations

Citation

Eisner, Leo (2001) A Reciprocity Method for Multiple Source Simulations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Y9S0-0S33. https://resolver.caltech.edu/CaltechETD:etd-08302001-030958

Abstract

This thesis develops and applies the reciprocity method to assess the seismic site and path effects at a chosen location of interest. To do this, we show that the reciprocity theorem is valid for this application, and develop a technique to represent velocity models of sedimentary basins. Using these tools we test the accuracy of synthetic seismograms computed for southern California. Finally, we apply the reciprocity technique to evaluate the site and path effects for three selected sites in southern California.

The first chapter describes the reciprocity method for simulating seismograms due to multiple earthquake sources at a site of interest. It shows a theoretical proof of the method and discusses the practical implementation and accuracy for the finite difference technique. The numerical tests show that the reciprocal simulations can be performed with the same level of accuracy as the forward calculations.

The second chapter develops a new methodology to represent models of sedimentary basins with extremely low near surface velocities by replacing these velocities with equivalent medium parameters for a finite frequency signal. The new model has a higher minimum velocity, which makes the numerical simulations feasible, and minimizes the difference between the seismograms from the original and new model.

The third chapter validates the velocity model by comparing synthetics and data. It applies the reciprocity method and compares the full waveform synthetic seismograms with a large number of weak motion data. The discrepancies between the predicted waveforms and the data are interpreted by analyzing the attributes of seismograms to find regions of the model that are in error.

Finally the reciprocity technique is applied to calculate site and path effects in the Los Angeles area for three selected sites by simulating 75 source scenarios on 5 major southern California faults. The largest amplitudes at the selected sites are obtained from earthquakes on local faults rather than an earthquake on the San Andreas fault.

Thesis Files