Dynamic triggering of remote, intermediate-depth earthquakes in the Mariana subduction zone following the 2012 Indian Ocean earthquakes
Abstract
Although remote dynamic triggering of shallow earthquakes has been well documented, there are no previous reported cases of remote dynamic triggering of intermediate-depth earthquakes. The mechanism producing intermediate depth earthquakes is still uncertain, so observations of dynamic triggering could provide important insights. The 2012 April 11 Indian Ocean M8.6 earthquake and the M8.2 aftershock were unusually prolific in triggering remote shallow earthquakes worldwide. Analysis of data from a temporary, amphibious array in the Mariana subduction zone reveals a dynamically-triggered earthquake sequence of intermediate-depth earthquakes following the M 8.2 aftershock. The first event occurs immediately after the long-period Rayleigh wave arrival. The intermediate-depth seismicity rate increases to 12 times the background seismicity rate in the hour immediately following and continues at twice the background seismicity rate for the subsequent 24 hours. A majority of the events identified in the first 24 hours have preliminary locations of 160-240 km depth and are clustered in the subducting slab beneath the Northern Mariana Islands.
Although previous studies of 2012 Indian Ocean earthquake remote triggering of shallow earthquakes suggested triggering by Love waves, the Mariana islands are near a maxima in the Rayleigh wave radiation pattern, and long period (T > 100 s) Rayleigh waves are stronger than Love waves on the array stations. This indicates that the sequence was triggered by Rayleigh waves. These results suggest that intermediate depth faults are critically stressed, such that extremely small strains can cause seismicity. The 2012 earthquakes may have been unusually productive in triggering earthquakes because the occurrence of two large earthquakes close in time may have increased the effective duration of the triggering strain, as proposed for shallow 2012 triggered events. Since intermediate depth earthquakes are attributed to dehydration reactions that involve changes in density, the association of intermediate depth triggering with Rayleigh waves raises the possibility that slight changes in density associated with the wave passage may have a role in triggering.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S41C0537P
- Keywords:
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- 7215 Earthquake source observations;
- SEISMOLOGYDE: 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS