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Incoming Plate and Forearc Structure of the East-Central Alaska-Aleutian Subduction Zone From 3D Local Earthquake Tomography

Session: Amphibious Seismic Studies of Plate Boundary Structure and Processes [Poster]

Type: Poster

Date: 4/20/2021

Presentation Time: 04:15 PM Pacific

Description: 

The Alaska Amphibious Community Seismic Experiment (AACSE) deployed 75 broadband ocean bottom seismometers and 30 land seismometers over the east-central Alaska peninsula region. This dense array was deployed for ~15 months between 2018 and 2019. The campaign crosses the Alaska-Aleutian subduction zone from the arc to the incoming Pacific plate, and encompasses the SW Kodiak segment, the Semidi segment, and part of the Shumagin seismic gap. These are segments with a history of large earthquake (> M7.4) ruptures, and distinct along-strike variations in plate locking fraction and seismic behavior. We aim to address whether these variations can be correlated with properties or geologic features that can be seismically imaged with the AACSE earthquake data. Are subducted seamounts, subducted fracture zones, variations in incoming plate hydration, or structural anomalies in the overriding plate associated with present-day seismic behavior of the plate interface? We will present 3-D seismic velocity (Vp, Vs, Vp/Vs) models of the region encompassed by the AACSE array. We use a local earthquake tomography code (LOTOS, Koulakov (2009), doi:10.1785/0120080013) and a catalog of P and S arrival times from events detected by the AACSE and other regional networks during the first four months of the AACSE deployment. To build our dataset we chose 1760 earthquakes, detected at 178 stations in the study region, with the criteria that events have at least 9 P-wave arrivals, 4 S-wave arrivals, a rms travel time residual less than 1.2 seconds, and are shallower than 150 km. Checkerboard tests show that structural anomalies in the horizontal plane are detectable down to at most ~30 by ~30 km. Results from the preliminary inversion for Vp and Vs structures show a first order boundary that likely corresponds to the top of the slab. These are promising initial results; at the 2021 SSA Annual Meeting we will present results from our on-going analysis.

Presenting Author: Liam Moser

Student Presenter: Yes

Authors