A Close Look at Slow and Fast Earthquakes Under the Aleutian Islands

Date: 4/24/2019

Time: 09:00 AM

Room: Cascade II

We use four mini seismic arrays and additional standalone seismic stations in the Unalaska and Akutan Island, Alaska, to capture the details of slow and fast earthquakes. The arrays are strategically placed to simultaneously image both subduction zone and volcanic seismicity. We find a prolific activity of tremor and repeating low frequency earthquakes (LFE). Interestingly, tremor occurs near-continuously in three patches generating the majority of the tremor on the plate interface. The tremor patches are located at the down-dip edge of the past large megathrust event. The tremor patches are separated by well-defined tremor gaps indicating strong lateral heterogeneity possibly in frictional properties. Unlike in other subduction zones, no clear episodic nature of tremor activity is observed. LFE families are located in the tremor zone, but occur in bursts. Tremor shows interesting slow and rapid migration patterns, in most cases, with both along-strike and along-dip components. Rapid tremor streaking is observed with velocities of several tens on kms per hour. Interestingly, tremor streaks are often characterized by abrupt reversals of migration direction without a significant change in velocity. In addition, tremor also migrates slowly at a velocity of 1 km/day for 3 months mostly along-strike but also with a significant along-dip component. Some of the migration features we see here have not been observed elsewhere. This area is also active in terms of regular fast earthquakes, making it an ideal place to study possible interaction between slow and fast earthquakes. We are exploring correlation between tremor/LFE activity and regular seismicity in space and time. Understanding their dynamics can provide new insights into the processes controlling a broad range of behaviors of fault slip.

Presenting Author: Abhijit Ghosh

Authors