Tremor and LFE activities using mini seismic array in the Alaska-Aleutian subduction zone

Bo LI, & Abhijit Ghosh

Published September 1, 2016, SCEC Contribution #6753, 2016 SCEC Annual Meeting Poster #215

Tremors and low frequency earthquakes (LFEs) have been well studied and observed as coupled phenomena in several subduction zones, such as the southwestern Japan, Cascadia and Costa Rica [Ghosh et al., 2012; Shelly et al., 2006; Brown et al., 2009]. In the Alaska-Aleutian subduction zone, the harsh weather conditions, the limited land and seismic station coverage, and the interference of the volcanic activities make it difficult to study tectonic (non-volcanic) tremor and LFE activities. In this study, we use continuous seismic data recorded by a mini array for two months to detect and locate tremors and LFEs. The array is composed of 11 stations with three components, deployed on Akutan Island in 2012. We use the beamprojection method [Ghosh et al., 2009; Ghosh et al., 2012] to automatically scan the continuous array data for tremors, and detect an average of 1.3 hours tremor activities per day. Then we use the local earthquakes recorded in the Advanced National Seismic System (ANSS) Composite Earthquake catalog during this period in the study region to calibrate the array. After calibration, the tremors locate into two clusters. The major one is located at the southern edge of the Unalaska Island and a smaller cluster to the southeast of the Akutan Island, with a gap around 30 km between them. Besides several visually detected LFEs, we apply a method similar to the beamforming network response method [Frank et al., 2014] to detect the LFEs using a sliding time window of 15 s, with a 0.025 s step. We detect hundreds of LFEs and classify them into 11 families. Then we use the LFEs detected as templates to search for the repeating LFEs over the two-month period by applying the matched-filter method. During the tremor activity, the LFEs show a much shorter interval time than non-tremor period. The locations of LFEs using first arrivals of P- and S-waves match well with the tremor clusters. To better understand the subduction fault dynamics, an additional mini array was installed in 2014 and another two are deployed in the summer 2015. The improved azimuth coverage enables us to detect and locate more tremors and LFEs, and provides us a good opportunity to study the spatiotemporal distribution of slow and fast earthquakes, and their potential connection in the Alaska-Aleutian subduction zone.

Citation
LI, B., & Ghosh, A. (2016, 09). Tremor and LFE activities using mini seismic array in the Alaska-Aleutian subduction zone . Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology