NSF Org:	EAR Division Of Earth Sciences
Recipient:	THE LELAND STANFORD JUNIOR UNIVERSITY
Initial Amendment Date:	April 29, 2003
Latest Amendment Date:	February 14, 2006
Award Number:	0309148
Award Instrument:	Continuing Grant
Program Manager:	Eva Zanzerkia EAR  Division Of Earth Sciences GEO  Directorate for Geosciences
Start Date:	June 1, 2003
End Date:	September 30, 2006 (Estimated)
Total Intended Award Amount:	$203,129.00
Total Awarded Amount to Date:	$203,129.00
Funds Obligated to Date:	FY 2003 = $101,375.00 FY 2004 = $101,754.00
History of Investigator:	Paul Segall (Principal Investigator) segall@stanford.edu
Recipient Sponsored Research Office:	Stanford University 450 JANE STANFORD WAY STANFORD CA  US  94305-2004 (650)723-2300
Sponsor Congressional District:	16
Primary Place of Performance:	Stanford University 450 JANE STANFORD WAY STANFORD CA  US  94305-2004
Primary Place of Performance Congressional District:	16
Unique Entity Identifier (UEI):	HJD6G4D6TJY5
Parent UEI:
NSF Program(s):	Geophysics
Primary Program Source:	app-0103  app-0104
Program Reference Code(s):	0000, OTHR
Program Element Code(s):	157400
Award Agency Code:	4900
Fund Agency Code:	4900
Assistance Listing Number(s):	47.050

ABSTRACT

EAR-0309148
Segall


Postseismic Processes Following the 1999 Chi-Chi, Earthquake and Models of Active Crustal Deformation in Taiwan

The Mw = 7.5, 1999 Chi-Chi, Taiwan earthquake occurred in the center of a dense GPS network. In the first 200 days after the earthquake displacements of as much as 10 cm accumulated in both the horizontal and vertical components. The dense spatial coverage and extraordinary signal to noise ratio make the postseismic deformation field of the Chi-Chi earthquake arguably the best ever recorded. Preseismic displacement rates provide unique information on the geometry and slip-rates of active faults, the earthquake loading cycle, and tectonics of an active arc continent collision.
Afterslip, viscous flow, and poroelastic relaxation have all been proposed to explain transient postseismic deformation. The data from the Chi-Chi earthquake is of such high signal to noise ratio that it is possible to discriminate between these processes. The early postseismic transient (3 months) is best explained by afterslip, however analysis of deformation over the subsequent years may reveal viscoelastic and/or poroelastic relaxation. Inversion results reveal that afterslip encircled the zone of large coseismic slip, consistent with stable slip being driven by stress changes caused by the earthquake. Inferred afterslip at seismogenic depths raises the question of why this slip occurred slowly rather than rapidly during the earthquake. Space-time inversions combined with mechanical models of slip consistent with laboratory derived friction laws will help to address this and should also elucidate fault zone properties and stresses.
Inversion of both the coseismic and postseismic GPS data are consistent with a ramp-flat geometry for the Chelungpu Fault. The geometry of active faults at greater depths is, however, not fully resolved. One difficulty has been that mechanically consistent models of interseismic deformation in compressional orogenic environments are needed. We propose to develop physical 2D viscoelastic models of the earthquake cycle in Taiwan, which include the first order effects of gravity, and in which the slip rates on faults are driven by far field plate motions rather than imposed kinematically. These models, combined with the available velocity field, will allow estimates of the geometry and slip-rates on active faults in Taiwan.

Please report errors in award information by writing to: awardsearch@nsf.gov.