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Earthquake Source Parameter Analysis Using Peak Narrow Band Displacement Amplitudes

Description: 

We present a source parameter analysis of nearly 13,000 earthquakes in the 2019 Ridgecrest sequence as part of the SCEC Stress Drop Validation Study. We measure an apparent spectrum defined as the maximum amplitude of the S-wave displacement seismogram after it is passed through a series of bandpass filters. From each seismogram we extract 17 peak amplitude measurements in half-octave bands between 0.125 and 46 Hz. The apparent spectrum is defined by the half-octave peak amplitudes. Given an S-wave arrival for each event, this workflow is fully automated and reproducible. We compare two different methods which use these spectra to measure stress drops.

In the first method, we obtain the source spectrum by applying corrections for site and path effects using a frequency-dependent distance correction based on Richter's local magnitude relation (-log(A0)). Our frequency-dependent attenuation relations account for geometric spreading, attenuation, and local site amplification. We fit an omega-squared Brune model to the median spectrum from all observing stations to obtain the moment and corner frequency for each event. In the second method, we take spectral ratios for close pairs of events to isolate the source effects. We employ the asymptotic spectral ratio method to measure relative stress drops using the high and low frequency levels. This has the benefit that we don’t need to resolve corner frequency, which also means we can compare earthquakes of similar magnitude. Using an inversion with all possible earthquake pairs, we compare relative stress drops to our first method. We find that moment magnitude can be reliably measured using both methods for earthquakes at least as small as Mw 1.0. We find an average stress drop of 3.3 MPa and a clear increase in average stress drop with magnitude.

Session: Understanding and Quantifying the Variability in Earthquake Source Parameter Measurements - I

Type: Oral

Date: 5/3/2024

Presentation Time: 08:45 AM (local time)

Presenting Author: Trey

Student Presenter: Yes

Invited Presentation: 

Authors