Repeating Earthquakes Trigger Themselves

Justin L. Rubinstein, & William L. Ellsworth

Published August 12, 2020, SCEC Contribution #10434, 2020 SCEC Annual Meeting Poster #089

Previous studies of repeating earthquake sequences in Parkfield, Taiwan, and Japan yield that repeating earthquake behavior is better predicted by a characteristic earthquake model with fixed inter-event time or fixed slip than it is by the time- and slip-predictable models. This implies that the elastic rebound model that underlies the time- and slip-predictable models offers no predictive information in an event-to-event sense. While we find no predictive power in the time- and slip-predictable models, there is a scaling between slip and the preceding recurrence time for some repeating earthquake sequences in Parkfield, whereby the magnitude increases with increasing inter-event time. We believe this scaling arises from an elastic behavior where the loading rate or coupling coefficient on a slip-patch instantaneously increases at the time of rupture and decays back to a constant rate over time. This would mean that the seismic slip budget would always be increasing, but it would accumulate more rapidly immediately following slip on the asperity.

To test this model, we analyze repeating aftershocks of the Parkfield earthquake. The repeating aftershocks of the Parkfield Earthquake were predominantly driven by afterslip, which was rapid at first and decayed logarithmically with time. This is similar to the event-event re-loading that we propose above. For the Parkfield aftershocks, we find short repeat times for the early aftershocks that progressively get longer. The magnitudes of the aftershocks, though, are consistent over time. Thus, we can conclude the temporally decaying loading combined with the increasing recurrence time produces the constant magnitudes. This is consistent with our hypothesis of the repeating earthquakes re-loading themselves. Thus, we can conclude that outside of mainshock-aftershock behavior, repeating earthquakes trigger themselves.

Key Words
repeating earthquakes, recurrence, creep, aseismic

Citation
Rubinstein, J. L., & Ellsworth, W. L. (2020, 08). Repeating Earthquakes Trigger Themselves. Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)