Source Parameter Analysis Using Maximum Amplitudes in the Time Domain

ABSTRACT We measure maximum amplitudes in the time domain on recordings of the 2019 Ridgecrest earthquake sequence to convert ground-motion amplitudes to source spectra. To do this, we modify Richter’s local magnitude relation to measure frequency-dependent empirical amplitude-decay curves and station corrections for a series of narrowband time-domain filters. Peak displacement amplitude in each frequency band is used to construct the displacement spectrum. After correction for attenuation, we determine corner frequency and moment from the resulting source spectra. By this approach, we measure moment magnitudes reliably to as small as ML 1.0. We find stress drop increases with both depth and magnitude and discuss whether this could be an artifact through assumptions about the source, path, and site.