HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by McNeill, A. F. Articles by Shragge, J. C. Search for Related Content GeoRef GeoRef Citation

The Effect of Forearc Mantle Serpentinization on Ground Motions from Megathrust and Intraslab Events in the Cascadia Subduction Zone

Department of Earth and Ocean Sciences
University of British Columbia
Vancouver, British Columbia, Canada
(A.F.M., M.G.B.)

Pacific Geoscience Centre
Geological Survey of Canada
Sidney, British Columbia, Canada
(G.C.R.)

Department of Geophysics
Stanford University
Stanford, California
(J.C.S.)

We re-examine large-scale structural controls on ground motions from megathrust and intraslab events in the Cascadia subduction zone in light of recent evidence pointing to a highly hydrated and serpentinized forearc mantle. We employ 2D P-SV pseudospectral synthetic seismograms, double-couple line sources, and a structural model for Cascadia based on the study of Bostock et al. (2002) that includes both serpentinized forearc mantle and eclogitized oceanic crust. As in a previous study (Cohee et al., 1991), we note that ground motions at greater epicentral distances are dominated by postcritical reflections from the Moho. However, in our modeling of megathrust earthquakes, we find that the presence or absence of serpentinized forearc mantle dictates whether maximum ground motions in the Pacific Northwest urban corridor (Portland, Seattle, Vancouver, Victoria) result from postcritical reflection at the oceanic Moho or continental Moho, respectively, as well as their range dependence. Moreover, serpentinization reduces the efficacy of the subducting oceanic crust as a wave guide by allowing energy to escape through the overlying wedge. This effect is particularly important for intraslab (Wadati-Benioff) events, as it allows focusing of upward-propagating energy toward the surface that would otherwise be redirected downward. Consequently, ground motions from intraslab sources at lower frequencies (0-2 Hz) can be up to 5 times greater than those modeled in the absence of a serpentinized forearc mantle. At higher frequencies, the lower Q of serpentine may act to reduce this amplification.

This article has been cited by other articles:

				V. M. Zobin and J. A. Pizano-Silva Macroseismic Study of the Mw 7.5 21 January 2003 Colima, Mexico, Across-Trench Earthquake Bulletin of the Seismological Society of America, August 1, 2007; 97(4): 1221 - 1232. [Abstract] [Full Text] [PDF]

				G. A. Ichinose, H. K. Thio, and P. G. Somerville Moment Tensor and Rupture Model for the 1949 Olympia, Washington, Earthquake and Scaling Relations for Cascadia and Global Intraslab Earthquakes Bulletin of the Seismological Society of America, June 1, 2006; 96(3): 1029 - 1037. [Abstract] [Full Text] [PDF]