A Time-Domain Approach for Accurate Spectral Source Estimation with Application to Ridgecrest, California, Earthquakes
Bulletin of the Seismological Society of America(2023)
摘要
We determine the seismic moment and corner frequency of earthquakes using narrowband, time-domain measurements of the maximum shear-wave displacement amplitude. Each S wave is passed through a set of one-octave band-pass filters between 0.25 and 32 Hz to measure the peak amplitude on the horizontal components. Following the development of Richter (1935) local magnitude scale, we derive a functional form of maximum amplitude versus distance, but separately for each frequency band, and use them to estimate wave attenuation as a function of frequency and distance. Attenuation is a strong function of frequency, approximately proportional to 1/f, with path averaged Q increasing (attenuation decreasing) with propagation distance. We use these empirical attenuation curves to correct the time-domain peak amplitudes to a reference distance of 10 km to recover the source spectrum. We find that the spectral shape is consistent with the Brune model, showing a well-defined plateau at low frequency and a decay at high frequency proportional to ω−2. We use the median spectrum for stations at distances up to 120 km for each event to measure the moment and corner frequency. This time-domain method provides a reliable and efficient way to accurately measure earthquake source parameters.
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关键词
accurate spectral source estimation,earthquakes,ridgecrest,time-domain
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