Remote Dynamic Triggering of Intermediate-Depth Earthquakes in the Mariana Subduction Zone Following the 2012 Indian Ocean Earthquake

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

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 6 minutes 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 locations of 160-240 km depth and are clustered in the subducting slab beneath the Northern Mariana Islands.

Although previous studies of remote shallow earthquake triggering by the 2012 Indian Ocean earthquakes suggested triggering by Love waves, calculated radiation patterns at intermediate depths show the Mariana Islands lie along the Rayleigh wave amplitude maxima, with maximum amplitudes at long periods (T > 100 s). Conversely, this azimuth corresponds to a Love wave node and amplitudes are small at all periods. The slight density change associated with the passage of the Rayleigh wave may have triggered dehydration reactions, which is associated with a proposed mechanism that produces intermediate-depth earthquakes, on optimally-oriented, critically stressed faults.

Presenting Author: Amanda Price

Authors