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Imaging the source region of Cascadia tremor and intermediate-depth earthquakes

Geoffrey A. Abers, Laura S. MacKenzie, Stephane Rondenay, Zhu Zhang, Aaron G. Wech and Kenneth C. Creager
Imaging the source region of Cascadia tremor and intermediate-depth earthquakes
Geology (Boulder) (December 2009) 37 (12): 1119-1122


The subduction of hydrated oceanic crust releases volatiles that weaken the plate boundary interface, trigger earthquakes, and regulate transient phenomena such as episodic tremor and slip (ETS). It is not clear how dehydration can separately induce earthquakes within the subducting plate and ETS, partly because few data exist on their relationship to subduction zone structures. We present results of a seismic experiment in the Washington Cascades, United States, that images a region producing both earthquake types. Migration of scattered teleseismic waves provides images of low-velocity subducting crust at depths <40-45 km with sharp boundaries above and below it. The sharp upper boundary indicates a layer of weak sediment or an overpressured fault zone that terminates abruptly downdip at 40-45 km depth. Regular earthquakes are at the top of the mantle within the downgoing plate everywhere the plate is <95 km deep, but ETS only exists where the sharp upper boundary occurs. The ETS location supports models of slow slip that require near-lithostatic fluid pressure, whereas regular earthquakes nucleate closer to the origin of metamorphic dehydration. Very low shear stresses on the plate boundary may limit seismicity to ETS and similar phenomena.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 37
Serial Issue: 12
Title: Imaging the source region of Cascadia tremor and intermediate-depth earthquakes
Affiliation: Lamont-Doherty Earth Observatory, Palisades, NY, United States
Pages: 1119-1122
Published: 200912
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 34
Accession Number: 2010-007904
Categories: SeismologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2009277
Illustration Description: illus. incl. sects., sketch map
N46°30'00" - N47°30'00", W124°30'00" - W120°30'00"
Secondary Affiliation: Schlumberger Data and Consulting Services, USA, United StatesMassachusetts Institute of Technology, USA, United StatesUniversity of Wyoming, USA, United StatesUniversity of Washington, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201005
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