HR: 14:25h
AN: T33E-04    [Abstracts]
TI: Slab-Forearc Density Structure and Rigidity Controlling the Seismogenic Behaviour Along the Peru-Chile Subduction Zone
AU: * Tassara, A
EM: andres@dgf.uchile.cl
AF: Departamento de Geofisica Universidad de Chile, Blanco Encalada 2002, Santiago, 00000, Chile
AU: Hackney, R
EM: rhackney@geophysik.uni-kiel.de
AF: Institut für Geowissenschaften Universität Kiel, Otto-Hahn-Platz 1, Kiel, 24118, Germany
AU: Legrand, D
EM: denis@dgf.uchile.cl
AF: Departamento de Geofisica Universidad de Chile, Blanco Encalada 2002, Santiago, 00000, Chile
AB: The rupture area and recurrence time of historical earthquakes along the Peru-Chile subduction zone and seismicity recorded by modern networks show a distinctive spatiotemporal distribution defining a characteristic segmentation of the seismogenic zone. It is unclear what factors control this segmentation. Knowledge about this topic is urgent to understand the processes generating devastating subduction earthquakes and to improve its hazard assessment. We are studying this problem for the Peru-Chile subduction zone from two perspectives. First, we applied a wavelet-based spectral isostatic analysis of topography and gravity to compute a high resolution map of the flexural rigidity along the subduction zone. This parameter is a function of the thermo- mechanical structure of both converging plates and the frictional properties of the subduction channel between them. Spatial variations on this map show correlation with the seismogenic segmentation, suggesting that rigidity and the associated physical factors play a fundamental role for the seismogenic behaviour along the margin. Second, we used an existing 3D density model to derive a map of vertical stress acting on the subducting slab below the forearc. This stress is a function of the thickness and density structure of the forearc resulting from long-term geological processes, and is the main component of the normal stress that regulates the magnitude of shear stresses to be released during earthquakes. The spatial variations of vertical stresses show significant correlations with the seismogenic segmentation, implying that the geologically-inherited density structure of the forearc is an important parameter for sustaining a time-persistent seismic segmentation. Of particular interest is the analysis of the giant (Mw 9.5) 1960 Valdivia earthquake, which nucleated in a region of high rigidity and high vertical stress and propagated southward into a region of very low rigidity and vertical stress. This could have important consequence for our understanding of the physical processes and factors interacting along seismogenic zones in general and the Peru-Chile trench in particular
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8140 Ophiolites (3042)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting