HR: 15:10h
AN: T33E-07    [Abstracts]
TI: Surface cracks as a long-term record of Andean plate boundary segmentation
AU: * Loveless, J P
EM: jpl34@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University, Snee Hall, Ithaca, NY 14853,
AU: Allmendinger, R W
EM: rwa1@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University, Snee Hall, Ithaca, NY 14853,
AU: Pritchard, M E
EM: mp337@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University, Snee Hall, Ithaca, NY 14853,
AB: Meter-scale surface cracks throughout the northern Chilean and southern Peruvian forearcs provide a long-term record of seismic segmentation along the Andean plate boundary. The cracks, mapped on high-resolution satellite imagery, show strong preferred orientations over large regions and the mean strikes of cracks vary systematically as a function of position along the margin. The spatial scale of this variation suggests that stress fields operating with similar dimensions, namely those produced by strong subduction zone earthquakes, are primarily responsible for crack evolution. The orientations of cracks are consistent with the static and dynamic coseismic stress fields calculated for several recent and historical earthquakes on distinct segments of the subduction interface. Field observations indicate that the cracks have experienced multiple episodes of opening and proximal age evidence suggests that they represent deformation as old as several hundred thousand years. We invert the crack orientation data to solve for plausible slip distributions on the Iquique, Chile segment of the margin (19°--23° S), which last ruptured in a M~8--9 event in 1877. We find that concentrations of coseismic slip resolved by the inversion coincide spatially with negative gravity anomalies, consistent with recent studies correlating subduction zone earthquake slip with forearc structure. These results suggest that distinct seismic segments or asperities on the subduction interface define characteristic earthquakes with rupture dimensions and magnitudes that are similar over many seismic cycles.
DE: 8010 Fractures and faults
DE: 8036 Paleoseismology (7221)
DE: 8104 Continental margins: convergent
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting