HR: 15:10h
AN: T53C-07 INVITED    [Abstracts]
TI: Signatures for Structural Asymmetry in Fault Zone Rocks from the San Andreas and the North Anatolian Fault Systems: Implications for Preferred Direction of Earthquake Ruptures
AU: * Dor, O
EM: dor@usc.edu
AF: University of Southern California, USC, Earth Sciences 3651 Trousdale Pkwy #117, Los Angeles, CA 90089-0740, United States
AU: * Dor, O
EM: dor@usc.edu
AF: Brown University, Geological Sciences, Brown University 324 Brook st., Providence, RI 02912, United States
AU: Ben-Zion, Y
EM: benzion@usc.edu
AF: University of Southern California, USC, Earth Sciences 3651 Trousdale Pkwy #117, Los Angeles, CA 90089-0740, United States
AU: Rockwell, T K
EM: trockwell@geology.sdsu.edu
AF: San Diego State University, Dept. Geological Sciences MC-1020 5500 Campanile Dr., San Diego, CA 92182-1020, United States
AB: Theoretical considerations indicate that earthquake ruptures on faults separating different solids have a preferred propagation direction (e.g., Weertman, 1980; Ampuero and Ben-Zion, 2007). Repeated occurrence of such ruptures is expected to lead to more shallow damage on the side of the fault with faster seismic velocities at depth (e.g. Ben-Zion and Shi, 2005). To test this hypothesis, expressions for structural asymmetry with respect to the slip zone of major faults in the southern San Andreas and the North Anatolian fault systems were observed and mapped at various scales in several sites along each fault. Geological mapping of shear fabric on a cm to meter fault core scale, subsidiary faults and fault rocks on a 10's of meters fault zone scale and pulverized rocks on a 100's of meters damage zone scale show systematically damage asymmetry. For the San Andreas, San Jacinto and Punchbowl faults the northeast side is more damaged. For of the 1943 and 1944 rupture zones on the North Anatolian fault, the south and north sides are more damaged, respectively. Similar sense of asymmetry for the San Jacinto fault was observed seismically for a ~100 m wide low velocity layer south of the our mapping sites (Lewis et al., 2005) and in a morphometric analysis of erosion patterns in the vicinity of our mapping sites (Wechsler et al., 2007). Asymmetric erosion patterns along the North Anatolian fault including the presence of almost all the river valleys length south of the fault along the 1943 rupture and vice-versa along 1944 rupture, strong asymmetry in drainage density and other related morphometric parameters between two correlative rock bodies on the two sides of the 1944 rupture, and significant difference in the density of gully networks in bad-land terrains across the 1943 rupture. All these signals are consistent with higher rock damage south and north of the 1943 and 1944 ruptures, respectively. The asymmetric damage patterns are compatible with preferred rupture directions northwestward on the examined fault sections of the southern San Andreas system, and eastward and westward on the 1943-1944 rupture sections of the North Anatolian fault, respectively (as occurred in these two recent North Anatolian fault earthquakes). Regional and local tomographic studies (e.g. Fuis et al., 2003; Scott et al., 1994) show that the more damaged northeast sides of the San Andreas and San Jacinto faults are on the blocks with faster seismic velocities at depth. Significant damage content in sedimentary rocks of the Juniper Hills formation on the southwest side of the San Andreas Fault in the central Mojave section indicates that dynamic generation of damage can occur very close to the surface of the Earth, in agreement with other indications for minimal exhumation of pulverized and other damaged fault zone rocks. These asymmetric damage patterns correlated to the velocity structure (where known) with shallow inferred generation depth are compatible with predicted outcomes for rupture along a bimaterial interface (Ben-Zion and Shi, 2005).
DE: 7209 Earthquake dynamics (1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8010 Fractures and faults
DE: 8012 High strain deformation zones
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting