Late Breaking Session: Ten-Million Years of Deformation along the Eastern California Shear Zone: Context and Characterization of the July 2019 Mw7.1 Ridgecrest Earthquake

Sunday, 22 September 2019
1:45 PM - 5:30 PM
North Ballroom 120D, North Building

SOUTHERN CONTINUATION AND TERMINATION OF THE AIRPORT LAKE FAULT

Program: Late Breaking
Time: 3:45 PM – 4:00 PM

Authors

Abstract

Aftershocks of the M7.1 event extend southward and end at the Garlock fault. Fresh fault scarps of Airport Lake fault go through the Spangler Hills and into Teagle Wash. They end 5.5 km before the Garlock fault but cracking in alluvial surfaces extends southward almost to the fault. Evidence of older left-lateral faulting can be followed to the Garlock fault.

Total right-lateral offset is marked well in Jurassic basement rocks in the Spangler Hills. A distinctive 10 m wide felsic dike intruding mafic plutonic rocks shows a total of ~5 km of right-lateral offset. This dike is a useful displacement marker because it strikes transverse to the faults, has steep dips, and a unique width. A set of narrower felsic dikes occurs parallel to the wide felsic dike is similarly displaced. Offset in older rocks is divided between 2.9 km on a structure coinciding with the main locus of earthquake ruptures, with an additional 2.1 km of left-lateral offset occurs on faults 1.4 km east of the main active scarp. A similar offset pattern is exhibited by the contact of hypabyssal rocks with mafic plutonic rocks as mapped by Jennings et al. (1962). Older (Pliocene(?)) gravel deposits of Smith (2009) may also show this offset pattern possibly as NE-trending paleovalleys, but the clast composition and other attributes need to be field investigated to support matching these gravel deposits.

M7.1 fault scarps continue south of the Spangler Hills into Teagle Wash. There are numerous small scarps in Holocene surfaces, as well as a small fault-bound playa lake. Closer to the Garlock fault a set of right-lateral faults offset Pliocene to Pleistocene strata but do not appear to affect the last glacial high stand lake shorelines of Searles Lake. The Pliocene formation of Pilot Knob Valley is right-laterally offset along two main strands of the Airport Lake fault. These strata were folded and uplifted along fold hinges parallel to the Garlock fault after their 3 Ma deposition. The eastern fault has right-lateral offset of 700 m of a NW-dipping ridge of the Pliocene strata. A parallel fault to the west has 350m of right-lateral offset. These faults can be followed to ~340 m away from the main trace of the Garlock fault where a strand of the Garlock fault left-laterally offsets them by 600 m.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-342036

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