Seismic Source Locations and Parameters for Sparse Networks by Matching Observed Seismograms to Semi-Empirical Synthetic Seismograms: Improvements to the Phase Spectrum Parameterization

The purpose of this study is to demonstrate the feasibility of full-waveform earthquake location using semi-empirical synthetic waveforms and received data from as few as two regional stations. We previously used a parameterization of the semi-empirical correction (or filter) that assumed range invariant phase spectrum of the correction term. That approach works very well if the two events are close (10 km). However, with greater event separation, the empirical filter is unable to correct the synthetic to match the data particularly at higher frequencies. By modifying the parameterization of the semi-empirical correction to allow for a range dependent phase spectrum, the empirical filter is able to correct the synthetic to match the data even when the event separation is large ( 50 km), and in particular, in cases where the range invariant phase correction fails. The improved parameterization characterizes the spectrum in terms of wave number and range. This approach requires us to isolate individual propagating modes as such. Currently, only the fundamental Rayleigh wave is used in this method, the ray-theory P-wave arrival time is used for time reference, the synthetic is lagged by the predicted arrival time, and the data uses the measured arrival time. With this technique, we are able to obtain GT5 or better locations using the long-period (30 second) Rayleigh waves. Also, we are able to simulate the waveforms from a nuclear explosion (JUNCTION) using the Little Skull Mountain Earthquake. We will present comparisons of the results using both the new approach and the old approach by utilizing ground truth (GT) for a data set of events in California. In particular, we will determine the range at which the accuracy of the new approach (using the long period surface waves) exceeds the old approach (using broadband signals). In addition, we will determine the separation at which the new phase parameterization is no longer able to simulate the observations. Presented at Seismic Research Review (28th): Ground-Based Nuclear Explosion Monitoring Technologies, SSR 2006, held in Orlando, FL on 19-21 Sep 2006 and published in proceedings of the same, v1, p484-492. The original document contains color images.