Fault Name Index
Eureka Peak Fault
TYPE OF FAULTING: right-lateral strike-slip
LENGTH: about 20 km
NEAREST COMMUNITIES: Yucca Valley, Joshua Tree
LAST MAJOR RUPTURE: June 28, 1992, Mw7.3; may have actually ruptured at the surface during a large aftershock
SLIP RATE: roughly 0.6 mm/yr
INTERVAL BETWEEN MAJOR RUPTURES: unknown
PROBABLE MAGNITUDES: MW5.5 - 6.8; larger when combined with other faults, as in 1992
OTHER NOTES: The Eureka Peak fault is a fairly short fault with a few significant claims to fame. First, the southernmost surface rupture during the Landers earthquake of 1992 (see below) occurred on this fault, breaking about 10 kilometers of the fault with a maximum surface offset of 21 centimeters. While a seemingly trivial point to note (compared to the offsets of several meters experienced elsewhere), this rupture actually marked the discovery of the Eureka Peak fault, as similar rupture revealed the existence of the nearby Burnt Mountain fault. Second, this fault probably handles a significant portion of the slip transferred from the San Andreas fault zone -- the Pacific/North American plate boundary -- to the Eastern California Shear Zone, northward across the Mojave, and may have been the fault responsible for the Joshua Tree earthquake in April 1992, which almost certainly prompted the Landers rupture to occur in June 1992.
The 1992 "Landers" rupture on the Eureka fault seems to have occurred in two separate (though very close together, timewise) events, followed by a period of "afterslip". The first ground breakage occurred some 30 seconds after the mainshock was felt in the Yucca Valley area. The second rupture episode was probably linked to a magnitude 5.6 aftershock less than 3 minutes after the Landers mainshock. Additional movement on the fault probably occurred in the form of afterslip.