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Measuring Source Parameters With Filtered Peak S-Wave Amplitudes Using the Asymptotic Spectral Ratio Method

Description: 

Measuring stress drop, a physical source characteristic that relates the average slip to fault size, is important for ground motion prediction and earthquake source physics. Different studies commonly find strong variability in stress drops within the same datasets, but much of this apparent variability arises due to difficulty in accurately measuring the corner frequency. As part of the community stress drop validation study, we present a method using spectral ratios and apply it to the Ridgecrest sequence. Stress drop ratios remove the common path and site effects from co-located events, to determine stress drop variability without the need to directly calculate corner frequencies. To form the ratios, we first calculate an earthquake’s observed frequency spectrum using maximum amplitudes in a series of band-pass filters on a displacement seismogram. Spectra determined this way have shown reliable moments and corner frequencies. From a pair of co-located events, we take the ratio of observed spectra, where the low-frequency asymptote is the ratio of the moments, and the high-frequency asymptote is the ratio of the slips. From these quantities we measure the stress drop ratio between both events. This method doesn’t rely on distinguishing corner frequencies, so unlike traditional spectral ratio methods, it can be used on earthquakes of similar size. These measurements will help determine how variable stress drops are, and have the potential to provide particular insight into potential differences in similar-sized events.

Session: Understanding the Variability in Earthquake Stress Drop Measurements [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Trey Knudson

Student Presenter: Yes

Invited Presentation: 

Authors