New Evidence for a Prehistoric Multi-Fault Rupture of the Calico-Hidalgo Fault System of the Southern Eastern California Shear Zone
Abstract
Complex multi-fault ruptures are a recently recognized form of heterogeneous fault zone behavior. Three such ruptures have occurred in the Eastern California Shear Zone (ECSZ) over the last few decades. The Landers, Hector Mine, and Ridgecrest ruptures all exhibited complex paths involving three or more major strike-slip faults of variable orientation connected by wide, complexly deformed stepovers. It is not clear whether complex, multi-fault ruptures are the norm for the ECSZ, nor whether they result from evolving tectonic conditions or instead are a standard expression of diffuse continental deformation. We have identified a fourth multi-fault sequence in the form of a pre-historic surface rupture on the Hidalgo-Calico fault system. We have mapped more than 20 km of rupture across multiple faults using satellite imagery, Structure from Motion topography, and field observations in the Marine Corps Air Ground Combat Center at Twentynine Palms, CA. The rupture appears as a continuous, irregular white lineament on aerial photos that cuts across alluvial and colluvial surfaces. This lineament corresponds to a zone of loose disturbance, which we interpret was formed by mole-tracks, anastomosing fissures, and subtle vertical scarps. Exposures in gullies along strike of the lineaments reveal fault gouge with steeply-dipping shear fabric. Numerous dextral shutter ridges and stream offsets occur along the zone, typically measuring 2-4 m. The preservation of the trace is likely short-lived (late Holocene?), given that it occurs in loose materials and cuts steep hillslopes, but is not preserved in active, bouldery washes. The trace is lost in soft, sandy alluvial surfaces on both ends, but we speculate that the original rupture was longer and may have even connected to the Holocene scarp along the Mesquite Lake fault 15 km to the south. Similarities in rupture path and slip-distribution with historical events supports the case that complex multi-fault ruptures are the kinematic norm for the evolving ECSZ. More work is required to assess whether these complex ruptures result from geometric or rheologic heterogeneities, dynamic stress triggering, or some other cause, as well as what these imply for seismic hazards.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMT040.0006G
- Keywords:
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- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 8107 Continental neotectonics;
- TECTONOPHYSICS;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS;
- 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS