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Rapid postseismic transients in subduction zones from continuous GPS

Melbourne, Timothy I. and Webb, Frank H. and Stock, Joann M. and Reigber, Christoph (2002) Rapid postseismic transients in subduction zones from continuous GPS. Journal of Geophysical Research B, 107 (B10). Art. No. 2241. ISSN 0148-0227. doi:10.1029/2001JB000555.

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Continuous GPS time series from three of four recently measured, large subduction earthquakes document triggered rapid postseismic fault creep, representing an additional moment release upward of 25% over the weeks following their main shocks. Data from two M_w = 8.0 and M_w = 8.4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting, and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep. Time series for another M_w = 7.7 event show 30% postseismic energy release, but here we cannot differentiate between afterslip and triggered deeper creep. A fourth M_w = 8.1 event, which occurred in the broad Chilean seismogenic zone, shows no postseismic deformation, despite coseismic offsets in excess of 1 m. For the three events which are followed by postseismic deformation, stress transferred to the inferred centroids (at 34, 60, and 36 km depths) by their respective main shock asperities increased reverse shear stress by 0.5, 0.8, and 0.2 bar with a comparatively small decrease in normal stress (0.01 bar), constraining the Coulomb stress increase required to force slip along the metastable plate interface. Deep triggered slip of this nature is invisible without continuous geodesy but on the basis of these earthquakes would appear to constitute an important mode of strain release from beneath the seismogenic zones of convergent margins. These events, captured by some of the first permanent GPS networks, show that deep moment release is often modulated by seismogenic rupture updip and underscore the need for continuous geodesy to fully quantify the spectrum of moment release in great earthquakes.

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Stock, Joann M.0000-0003-4816-7865
Additional Information:© 2002 American Geophysical Union. Issue published online: 22 Oct 2002; Article first published online: 22 Oct 2002; Manuscript Accepted: 9 Jan 2002; Manuscript Revised: 5 Jan 2002; Manuscript Received: 7 May 2001. We thank Osvaldo Sanchez of the Autonomous University of Mexico (UNAM) for supplying the tide gauge data. Discussion with Jeanne Hardebeck on Coulomb stress transfer was very helpful. Figures were generated with Generic Mapping Tools [Wessel and Smith, 1991]. Jalisco field work was supported under NSF grant EAR-9527810 to J. Stock, while data analysis of subsequent earthquakes was supported under NSF grant EAR-9973191 to T. Melbourne.
Group:Seismological Laboratory
Funding AgencyGrant Number
Subject Keywords:subduction zone; earthquake; postseismic; moment release
Issue or Number:B10
Record Number:CaltechAUTHORS:20140415-125909434
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Official Citation:Melbourne, T. I., F. H. Webb, J. M. Stock, and C. Reigber, Rapid postseismic transients in subduction zones from continuous GPS, J. Geophys. Res., 107(B10), 2241, doi:10.1029/2001JB000555, 2002.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44961
Deposited On:16 Apr 2014 14:32
Last Modified:10 Nov 2021 16:58

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