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Using Low-Frequency Earthquake Families on the San Andreas Fault as Deep Creepmeters

Amanda Thomas, N. M. Beeler, Quentin Bletery, Roland Bürgmann, & David R. Shelly

Published January 22, 2018, SCEC Contribution #7965

The central section of the San Andreas fault hosts tectonic tremor and low-frequency earthquakes (LFEs) similar to subduction zone environments. LFEs are often interpreted as persistent regions that repeatedly fail during the aseismic shear of the surrounding fault allowing them to be used as deep creepmeters. We test this idea by using the recurrence intervals of individual LFEs within LFE families to estimate the timing, duration, recurrence interval, slip, and slip rate associated with inferred slow slip events (SSEs). We formalize the definition of a creepmeter and determine whether this definition is consistent with our observations. We find that episodic families reflect surrounding creep over the interevent time while the continuous families and the short timescale bursts that occur as part of the episodic families do not. However, when these families are evaluated on timescales longer than the interevent time these events can also be used to meter slip. A straight-forward interpretation of episodic families is that they define sections of the fault where slip is distinctly episodic in well defined SSEs that slip 16 times the long term rate. In contrast, the frequent short-term bursts of the continuous and short-timescale episodic families likely do not represent individual creep events but rather are persistent asperities that are driven to failure by quasi-continuous creep on the surrounding fault. Finally we find that the moment-duration scaling of our inferred creep events are inconsistent with the proposed linear moment-duration scaling. However, caution must be exercised when attempting to determine scaling with incomplete knowledge of scale.

Thomas, A., Beeler, N. M., Bletery, Q., Bürgmann, R., & Shelly, D. R. (2018). Using Low-Frequency Earthquake Families on the San Andreas Fault as Deep Creepmeters. Journal of Geophysical Research: Solid Earth, 123(1), 457-475. doi: 10.1002/2017JB014404.