INVESTIGATING IMPACTS OF SLOW SLIP EVENTS ON GPS STATION VELOCITY AND SUBDUCTION ZONE COUPLING IN CASCADIA

GPS stations anchored across the Olympic Peninsula in Washington have been recording daily position data for the past 20 years, showing overall eastward movement as strain accumulates on the overriding plate of the Cascadia subduction zone. Approximately every 11-19 months, motion reverses during a Slow Slip Event, or SSE. This study seeks to identify patterns in station velocities before and after the SSEs: whether the eastward velocity following an event is consistent with that prior to the event, and whether motion has a signature change before a SSE that could allow prediction of SSEs and could give insight into what controls the occurrence of SSEs.

The first critical step of investigating inter-event velocities was to identify and remove the SSEs from the position time series. Previously, SSEs had been identified visually, and each event was defined by the first and last day any GPS station felt the event. Here we present an algorithm to objectively and consistently identify the SSEs station by station, which allows for spatial variation in how strongly the events were felt, while still including checks to filter out false positives from noisy data. We identify patterns in velocities both spatially and temporally, at regional levels and for individual stations. Significantly, inter-event velocity vectors have rotated clockwise since 1996, particularly in the eastern Olympic Peninsula, which may suggest a change in coupling patterns on the Cascadia subduction zone.

Session No. 33--Booth# 4

Structural Geology and Tectonics (Posters)

Tuesday, 22 March 2016: 8:00 AM-12:00 PM

Convention Hall (Empire State Plaza Convention Center)

Geological Society of America Abstracts with Programs. Vol. 48, No. 2
doi: 10.1130/abs/2016NE-272177

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