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Estimating earthquake source parameters from S-wave maximum amplitudes: Application to the 2019 Ridgecrest sequence

Ian Vandevert, Peter M. Shearer, & Wenyuan Fan

Submitted September 10, 2023, SCEC Contribution #13112, 2023 SCEC Annual Meeting Poster #033

Earthquakes rupture in complex ways, radiating a wide spectrum of seismic energy. The rupture complexities are reflected in earthquake stress drops. Spectral decomposition is a popular approach to resolve earthquake stress drops, in which the source spectra are separated from station and path effects and fit to a theoretical source model. The method is effective in estimating relative stress drops for a group of earthquakes spanning a broad range of magnitudes, when large data sets of earthquakes and receivers are available. However, poor signal-to-noise ratios at low frequencies for smaller earthquakes prevents spectral decomposition from accurately measuring the moments and corner frequencies of the larger events, which require unbiased low-frequency constraints. Here we experiment with a new method termed amplitude decomposition, which first measures the maximum shear-wave amplitude of bandpass-filtered seismograms as a function of event-dependent effects, station-dependent effects, and path effects. We then assemble the decomposed results in the frequency domain and infer stress drops for a group of closely located earthquakes. The method can reliably measure source spectra at lower frequencies, allowing for better estimation of source parameters. We apply the method to the 2019 Ridgecrest earthquake sequence and estimate uncertainties of the source parameters. We find that seismic moment is more accurately inferred for the larger events, and that in some cases more reliable estimates for earthquake source parameters can be inferred. We plan to apply this method to larger datasets and those in other regions, which will help in understanding the distribution of source parameters, including differences resulting from fault types and geologic setting.

Vandevert, I., Shearer, P. M., & Fan, W. (2023, 09). Estimating earthquake source parameters from S-wave maximum amplitudes: Application to the 2019 Ridgecrest sequence. Poster Presentation at 2023 SCEC Annual Meeting.

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