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A search for tremor-like precursors to earthquakes in southern California

Jessica C. Hawthorne, & Jean Paul Ampuero

Published 2014, SCEC Contribution #6053

We conduct a search for tremor-like precursors to M>3 earthquakes in southern California. We use a frequency-domain phase coherence technique to examine the seismograms in the minutes to seconds before each of about 5000 earthquakes. This approach allows us to identify signals coming from the same location as the earthquake. It uses recordings at multiple stations to identify coherence even when the source-time functions are complicated. If the signals recorded just before an earthquake have the same Green's functions as the earthquake, they should have a high phase coherence with the earthquake records. They should also have high phase coherence with the records of nearby earthquakes. We usually compare potential precursors with nearby earthquakes because temporally persistent noise sources create a bias when we compare the potential precursor with the mainshock.

This method successfully detects previously identified foreshocks. However, among the 5000 earthquakes examined so far, we see no evidence for additional precursory signals. For more than half of these earthquakes, error estimates suggest that we should be able to detect signals with durations of 5 seconds and energy equivalent to a M1 earthquake. We are continuing to examine more earthquakes and to consider the uncertainty introduced by using nearby earthquakes as templates.

Hawthorne, J. C., & Ampuero, J. (2014). A search for tremor-like precursors to earthquakes in southern California . Poster Presentation at 2015 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics