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Ground motion coherence study in multiple distance ranges and frequency bands

Lei Qin, Yehuda Ben-Zion, & Frank L. Vernon

Published August 14, 2017, SCEC Contribution #7581, 2017 SCEC Annual Meeting Poster #032

We analyze one year of continuous waveform data from the Pinon Flats Observatory Array (PY) and Dry Wash linear array (DW) across the San Jacinto fault. PY consists of 13 broadband sensors arranged on three circles with station separated by about 65m, 330m, and 780m. DW is a linear array across the Clark fault in the trifurcation area of the San Jacinto fault zone with 12 short-period sensors separated by about 25m. The examined data include ambient seismic noise and signals generated by teleseismic and local earthquakes. We use multitaper spectral analysis to study the coherence of ground motion in various distance ranges and frequency bands. Noise data are highly coherent in 0.1-1.0Hz when station distance is as small as 65m, and earthquake signals exhibit high coherence in a wider frequency band. The coherence decreases quickly outside the dominant frequency band and with increasing station distance. The high coherence frequency bands exhibit seasonal variations with complex detailed patterns. The coherences functions from PY show high anomalies in ~2-4Hz ~20 days before the 2016 Mw5.2 Borrego Springs event. The coherence from the southern-most DW station pair is low over a wide frequency band, starting ~35 days before the event and lasting for >60 days. The coherence of certain components from several other DW station pairs also show low anomalies starting at different time before the event with different amplitudes and durations. Updated results will be presented in the meeting.

Qin, L., Ben-Zion, Y., & Vernon, F. L. (2017, 08). Ground motion coherence study in multiple distance ranges and frequency bands. Poster Presentation at 2017 SCEC Annual Meeting.

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