Triggering at an Alaska-Aleutian Arc Tremor Sweet Spot
Abstract
Relative to other regions of the Alaska-Aleutian arc, daily routine visual scanning done for volcano monitoring notes signals with characteristics indicative of tectonic tremor most commonly at stations in the vicinity of Akutan Island. Brown et al. (2012, in press) found ambient tremor in four regions along the Alaska-Aleutian arc, and a total tremor duration in the vicinity of Akutan almost double that in any of the other regions examined. We further tested the inference that the vicinity of Akutan Island is a 'sweet spot' for tremor generation, by examining the tremor response to the nine largest amplitude seismic wavefields recorded across the region since 2006. The three largest of these posited triggering dynamic deformations originated from a M7.2 regional, the 2007 M8.1 Kuril and the M9.0 Tohoku, Japan earthquakes. Clear triggered tremor, bursts of 2-10 Hz energy in sync with passing lower-frequency surface waves, is observed only at seismic stations on Akutan and adjacent islands for the latter two earthquakes. While high frequencies from the triggering waves of the regional earthquake prevent detection of possible triggered signals at Akutan and its neighbors, no triggering is observed at any more distant stations. The only other clear triggered tremor - also at Akutan and its nearest neighbor - is associated with the 2012 M8.6 Sumatra earthquake wavefield, which curiously has smaller amplitudes than other wavefields that did not trigger tremor anywhere within the study region. Since tremor may be a proxy for slow slip on the plate-interface, we hypothesize that this observation suggests slow slip was underway at the time of the Sumatra earthquake and are testing this using GPS data. We also explore other possible explanations, such as differences in the posited triggering wavefields. We conclude that the Akutan region is indeed a sweet spot for tremor, perhaps consistent with its location above a frictionally transitional plate-interface, modeled as almost fully decoupled to the west and down-dip and coupled to the east and up-dip (bounding the down-dip edge the M8.9 1957 rupture). Curiously the Akutan region also straddles the transition between continental and oceanic crust within the overriding plate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.S33B2553G
- Keywords:
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- 7240 SEISMOLOGY / Subduction zones;
- 8118 TECTONOPHYSICS / Dynamics and mechanics of faulting;
- 8123 TECTONOPHYSICS / Dynamics: seismotectonics;
- 8170 TECTONOPHYSICS / Subduction zone processes