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Vidale, J. E.
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Vidale, J. E.
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- PublicationRestrictedCascadia Tremor Located Near Plate Interface Constrained by S Minus P Wave Times(2009-01-30)
; ; ; ; ; ; ; ;La Rocca, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Creager, K. C.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA. ;Galluzzo, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Malone, S.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA. ;Vidale, J. E.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA. ;Sweet, R.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA. ;Wech, G.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA.; ; ; ; ; ; Nonvolcanic tremor is difficult to locate because it does not produce impulsive phases identifiable across a seismic network. An alternative approach to identifying specific phases is to measure the lag between the S and P waves. We cross-correlate vertical and horizontal seismograms to reveal signals common to both, but with the horizontal delayed with respect to the vertical. This lagged correlation represents the time interval between vertical compressional waves and horizontal shear waves. Measurements of this interval, combined with location techniques, resolve the depth of tremor sources within T2 kilometers. For recent Cascadia tremor, the sources locate near or on the subducting slab interface. Strong correlations and steady S-P time differences imply that tremor consists of radiation from repeating sources.300 31 - PublicationRestrictedTidal Modulation of Nonvolcanic Tremor(2007-11-22)
; ; ; ; ; ;Rubinstein, J. L.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA ;La Rocca, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Vidale, J. E.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA ;Creager, K. C.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA ;Wech, A. G.; Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA; ; ; ; Episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of Japan and Cascadia. In Cascadia, such episodes typically last a few weeks, and differ from “normal” earthquakes in their source location and momentduration scaling. The three most recent episodes in the Puget Sound/Southern Vancouver Island portion of the Cascadia subduction zone have been exceptionally well recorded. In each episode, we see clear pulsing of tremor activity with periods of 12.4 and 24-25 hours, the same as the principal lunar and lunisolar tides. This indicates that the small stresses associated with the solid-earth and ocean tides influence the genesis of tremor much more effectively than they do “normal” earthquakes. Because the lithostatic stresses are 105 times larger than those associated with the tides, we argue that tremor occurs on very weak faults.284 27