HR: 0800h
AN: T31C-1322    [Abstracts]
TI: Horizontal Displacement of the Hector Mine Earthquake, (California, 16/10/99, Mw 7.1), Derived from Aerial Photography Intercorrelation
AU: * Lorne, A
EM: lorne@ipgp.jussieu.fr
AF: Lab. Tectonique - IPGP, UMR7875 - BP89 4, place Jussieu, Paris, 75005 France
AU: Klinger, y
EM: klinger@ipgp.jussieu.fr
AF: Lab. Tectonique - IPGP, UMR7875 - BP89 4, place Jussieu, Paris, 75005 France
AU: Binet, r
EM: renaud.binet@cea.fr
AF: LDG/CEA, BP12, Bruyeres le Chatel, 91680 France
AU: michel, r
EM: remi.michel@cea.fr
AF: LDG/CEA, BP12, Bruyeres le Chatel, 91680 France
AB: Surficial slip distribution is a key parameter to understand earthquake source processes. GPS, InSAR and field works are the most common methods used to derive the slip function. However, each of those methods bears severe limitation, respectively the small number of measurements, the decorrelation close to the rupture, and the difficulty to estimate the amount of distributed deformation in the rupture zone. Here we apply optic image sub-pixel intercorrelation technique with high resolution aerial photography from USGS to derive the slip function of the Hector Mine earthquake (California, 16/10/99, Mw 7.1). This new technique provides independent measurement of the horizontal displacement every 16 m along the entire rupture length with no near-field saturation problem. We used 15 low altitude air photo pairs (images acquired between 1989 and 2002) to produce a map of the rupture. This map is almost identical to the field survey data where available; the map also images segments that had been assumed from seismologic data but not identified in the field, probably due to distributed deformation in unconsolidated sediments. Slip distribution along the rupture was measured from profiles perpendicular to the fault, and averaged on 500 m long patches. The measurement accuracy varies between 10 and 50 cm according to the area, allowing us to image slip variation at the scale of few km. A systematic correspondence can be established between slip variations and changes in the geometry of the rupture, like bifurcation or change in azimuth. Particularly, two peaks of slip are observed: the first one about 5 m of slip, located 2 km south of the epicenter, and the second one about 4 m of slip, located about 10 km north of the epicenter, with a local minimum of 3 m between the two peaks. This local minimum is probably due to the existence of the second rupture where the epicenter is located. We measured horizontal slip on this branch up to 1 m, whereas almost no slip has been measured in the field. In detail, slip measurements in bedrock areas are in good agreement with field data whereas in sediments, our data are up to 2 m larger. We interpret this discrepancy as the difficulty to estimate the distributed deformation during field measurements when our technique has no difficulty to integrate this deformation. Finally, due to the accuracy of our technique, the slip-curve we propose reconcile surficial displacement measurements with the slip distributions modeled from seismologic, InSAR and GPS data, especially concerning the existence and location of the peaks of larger slip.
DE: 9350 North America
DE: 7230 Seismicity and seismotectonics
DE: 1242 Seismic deformations (7205)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting