M 6.1 1993 Eureka Valley Earthquake; Listric Normal Faulting Constrained from 
Aftershock Relocations and Teleseismic Body Wave Models

Abstract Author(s): Donghong Pei (pei@unr.edu; Nevada Seismological Laboratory, 
MS 174 University of Nevada, Reno, NV 89557), Gene Ichinose (URS Corporation, 
566 El Dorado St. 2nd Floor, Pasadena, CA 91101-2560) and Ken Smith (NSL-UNR)

Abstract: Eureka Valley is located in the northern Eastern California Shear 
Zone in a 
structurally complex region west of the transition between the Furnace Creek 
Fault Zone (FCFZ) and Fish Lake Valley Fault Zone (FLVFZ) and east of the Owens 
Valley Fault Zone (OVFZ).  These major high-slip rate Basin and Range dextral 
systems strike north-northwest. Minor mapped in the EV Valley area that 
accommodate slip transfer associated with these major systems strike both north 
and northeast and show predominantly normal slip.  The M 6.1 May 17, 1993, 
Eureka Valley mainshock (23:20 UTC) was followed by more than 2800 located 
aftershocks over the next five years.  The network density in the Eureka Valley 
area is relatively poor but control on aftershock activity was supplemented by 
portable instrumentation deployed by CalTech and UNR. Regional moment tensor 
solutions for the mainshock from long-period surface are consistent with a 
north-northeast striking 30-60 degree west dipping normal fault.  The 
approximately 20 km long aftershock zone is unusual for an M 6.1 event with 
rupture propagating from north to south.  Detailed aftershock locations and 
teleseismic body wave modeling suggest a component of listric normal faulting. 
Aftershock locations image a concave-upward shaped fault plane changing strike 
southward, that dips west at a lower angle (~20 degree) at depth than near the 
surface.  The complexity is also observed along strike in the aftershock data, 
where the north section (near the hypocenter) dips more steeply than the 
southern end of the rupture.  Forcing a two source solution in modeling 
teleseismic body waves results in a north striking normal faulting source 
dipping 50 degrees west at the north end near the hypocenter but striking 
northeast at a low angle at the southern extent of fault rupture in agreement 
with the fault geometry from aftershock relocations.