Serving professionals in engineering, environmental,
and groundwater geology since 1957

Click here for more details

Date: ***Tuesday, June 12th***
Topic: Pulverized rocks and the depth of dynamic damage generation along the Mojave section of the San Andreas Fault

Speaker: Ory Dor, Department of Earth Sciences, University of Southern California

Location: Steven's Steak House, 5332 Stevens Place, Commerce, CA
Time: 6:00 p.m.-Social Hour; 7:00 p.m.-Dinner; 7:45 p.m.-Presentation
Cost: $30 per person with reservations, $35 at the door, $15 for students with a valid Student ID
Reservations: ***Please call Jon Relyea at (800) 554-3205
or email***

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 that the northeast side of the San Andreas, San Jacinto and Punchbowl faults, and the south and north sides of the 1943 and 1944 rupture zones on the North Anatolian fault, respectively, are more damaged. Similar sense of asymmetry for the San Jacinto fault was observed in tomographic imaging of a ~100 m wide low velocity layer south of the small scale geological mapping sites (Lewis et al., 2005). 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 the 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 are also consistent with higher damage content south and north of the 1943 and 1944 ruptures, respectively. The asymmetric damage patterns are compatible with preferred rupture directions northwestward on faults of the San Andreas Fault system, and westward and eastward on the 1943-1944 rupture sections of the North Anatolian faults, 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 side of the of the San Andreas and San Jacinto faults is on the block 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. An asymmetric shallow damage structure correlated with the velocity structure at depth is compatible with theoretical predictions of the theory for rupture along bimaterial interface (Ben-Zion and Shi, 2005). Microfractures in the Juniper Hills rocks near the fault, orientated preferably normal to its strike, are compatible with the transient stress field associated with seismic slip events on frictional rough surfaces (Chester and Chester, 2000). The damage fabric of those rocks is anisotropic and not compatible with an absolute tension.

Structural analysis of the orientation and slip data of 115 slip surfaces in the granitic hanging-wall of the Sierra Madre fault shows that their geometry and kinematics are compatible with the plastic respond predicted by Rice et al. (2005) to the violation of Mohr-Coulomb yielding criterion associated with the stress field of propagating mode II ruptures with slip weakening and a self-healing pulse.
Mr. Ory Dor completed undergraduate studies at the Hebrew University in Jerusalem, Israel followed by research exploring fresh and reactivated rupture zones in South African deep mines. Mr. Dor is currently completing a PhD program at the University of Southern California working on multi-scale & signal study of fault zone structure with implications for the mechanics of faulting and earthquakes. Mr. Dor is interested in the nature of earthquake signature as it is expressed by fault zone rocks, by the extent and structure of damage at different scales, and by symmetry properties of fault zones. The work at USC included multi-scale mapping of fault zones of the San Andreas and North Anatolian Fault systems. Mr. Dor uses meso-scale mapping at natural and artificial exposures, regional mapping of pulverized rocks, thin sections, image analysis, GIS analysis and structural analysis methods to infer about the symmetric properties of fault zones, preferred rupture propagation direction, the properties of the newly-defined pulverized fault zone rocks, and to provide constraints for the depth of dynamic damage generation. Post-doc work including rock mechanics experiments with fault zone rocks is planned at Brown University in Providence, RI.