Aftershock Sequences of Intermediate-Depth Earthquakes Beneath Japan

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Deep earthquakes have been observed to have fewer aftershocks than shallow earthquakes. To determine whether the observed differences are real or due to observational constraints, we study intermediate-depth aftershock sequences beneath Japan using the Japan Meteorological Agency (JMA) earthquake catalog from May 2002 through February 2016. We identify 17 intermediate-depth earthquakes (70-305 km depth) with local magnitude MJ >= 5.7 for further analysis. The mainshocks typically occur at the edges of patches with high background seismicity rates and the aftershocks tend to occur within the same patches. For the high-seismicity and aftershock volume around each earthquake, we calculate the cumulative number of earthquakes with time and the seismicity rate for earthquakes above the magnitude of completeness. For 7 of the earthquakes, we observe aftershock sequences similar to those for shallow earthquakes: the number of earthquakes increases immediately following the earthquake and exponentially decays with time with a p value of ~1. In contrast to shallow aftershock sequences, the magnitude differential between the mainshock and largest aftershock is typically 2-3.5 units. This large magnitude differential would prevent us from observing most aftershocks for the remaining 10 earthquakes. Using an earthquake catalog with a magnitude of completeness 4-5 units below the mainshock magnitude, we are able to observe productive aftershock sequences for intermediate-depth earthquakes beneath Japan.

Presenting Author: Linda M. Warren

Authors