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Do earthquakes talk to each other?: Triggering and interaction of repeating sequences at Parkfield

Kate H. Chen, Roland Bürgmann, & Robert M. Nadeau

Published 2013, SCEC Contribution #1687

Knowledge of what governs the timing of earthquakes is essential to understanding the na- ture of the earthquake cycle and to determining earthquake hazard, yet the variability and con- trols of earthquake recurrences are not well established. The large population of small, charac- teristically repeating earthquakes at Parkfield provides a unique opportunity to study how the interaction of earthquakes affects their recurrence properties. We analyze 112 M -0.4 ~ 3.0 re- peating earthquake sequences (RESs) to examine the triggering effect from nearby microseis- micity. We find that the repeating events with a smaller number of neighboring earthquakes in their immediate vicinity tend to recur in a more periodic manner (i.e., the coefficient of varia- tion in recurrence intervals is less than 0.3). The total static stress perturbation from close-by earthquakes, however, does not seem to strongly influence RES regularity. The uneven distri- bution of stress changes in time has a modest but significant impact on recurrence intervals. A significant reduction of recurrence intervals occurs in the case of very high stress changes from neighboring events. Close-by-events influence RES timing in a matter of several days or less by short-term triggering. Events that occurred within less than one day of an RES often im- posed or experienced high stress changes. A static stress increment of ~30 kPa can be enough to produce such short-term triggering. We find that the triggered repeating events are often near the end of their average earthquake cycle, but some events occur following a substantially shortened interval. When comparing the accelerated occurrence at the time of RES events fol- lowing neighboring events with varying magnitudes, we find that the distance of short-term triggering increases from < 1 km to 4 km for M1 to M4 events.

Chen, K. H., Bürgmann, R., & Nadeau, R. M. (2013). Do earthquakes talk to each other?: Triggering and interaction of repeating sequences at Parkfield. Journal of Geophysical Research, 118(1), 165-182. doi: 10.1029/2012JB009486.