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Subduction Zone Interface Structure Beneath Kodiak Island, Alaska: Constraints from Receiver Functions Across a Spatially Dense Node Array

Session: Recent Development in Ultra-Dense Seismic Arrays with Nodes and Distributed Acoustic Sensing [Poster]

Type: Poster

Date: 4/20/2021

Presentation Time: 04:15 PM Pacific

Description: 

Kodiak Island is an exposed part of an accretionary complex along the Alaska-Aleutian subduction zone that formed as the Pacific plate subducted below the North American plate. Subduction of the Pacific plate beneath Alaska has produced more >M8 earthquakes than any other plate boundary system during the last ~100 yrs, including the 1964 M9.2 Great Alaska earthquake. Kodiak Island lies on a section of the subduction zone that ruptured in the 1964 event and experiences seismic tremor, suggesting multiple modes of plate interface slip. Unconsolidated sediment thickness and fluid distribution along the subduction zone interface are some of the factors thought to affect slip stability. We use Ps receiver functions to identify potential low seismic velocity anomalies and estimate Vp/Vs within the oceanic crust to constrain metamorphism and fluid pressure. The study will allow us to test the hypothesis: Two distinct layers will compose the plate interface beneath Kodiak Island, a shallower LVL related to sediment subduction, and an oceanic layer that has higher velocity than the sediment but lower velocity than the underlying oceanic mantle. In May 2019, we deployed 398 autonomous three-component 5-Hz Fairfield Nodal Zland geophones on Kodiak Island as part of the Alaska Amphibious Community Seismic Experiment. The dense lines consisted of nodes at approximately 200-m spacing recording continuously for about 30 days adjacent to the ~40 km-long Chiniak Highway system across northeastern Kodiak Island. A total of 86 events with an MW > 5.0 were recorded during that time period with 12 events having an MW > 6.0 and an epicentral distance between 30° and 90°. Preliminary imaging results show the continental Moho, the top of the subducting Pacific Plate, the slab Moho and a highly variable amplitude positive arrival between 1 and 10 km that extends the entire length of the profile.

Presenting Author: Evans A. Onyango

Student Presenter: Yes

Authors