Southern Surface Rupture Associated with the M 7.3 1992 Landers, California, Earthquake
Although most evidence suggests that the 28 June 1992 M 7.3 Landers earthquake ruptured unilaterally north, significant surface rupture was mapped on the Eureka Peak and Burnt Mountain faults, to the south of the Landers epicenter. An eyewitness account reports that surface rupture occurred on the northern Eureka Peak fault within approximately 35 sec of the mainshock initiation. Array analysis of the Landers mainshock provides evidence in support of this report; a significant southern subevent in the early mainshock coda. I also analyze dense array recordings of a M 5.6 aftershock that occurred 3 min after the mainshock at 34°7.65′N, 116°23.82′W and show that there is strong evidence that this event was also associated with significant rupture on the Eureka Peak fault. This analysis thus suggests that the Eureka Peak fault rupture was not caused by direct bilateral mainshock rupture but instead was initially triggered less than a minute after the mainshock and reruptured by the M 5.6 aftershock. Results for the evolution of the Landers sequence suggest that mainshock subevents may in some cases be accurately described as aftershocks (i.e., disjoint triggered events) that occur within the duration of mainshock strong ground motion.
© 1994, by the Seismological Society of America. Manuscript received 28 June 1993. E. Sembera, G. Glassmoyer, C. Mueller, and S. Lydeen are gratefully acknowledged for their efforts in instrument deployment, maintenance, and data playback. I acknowledge the cooperation and patience of C, Schultz, G. Whitney, R. Skaggs, and the employees of the Morongo Valley Community Center, and thank J. Treiman, M. Rymer, A. Frankel, J. Mori, P. Spudich, K. Sieh, and D. Eberhart Phillips for helpful discussions, Egill Hauksson for providing his event relocation for the Yucca Valley aftershock, and P. Bodin for calling attention to the southern rupture mapping efforts by J. Treiman. I thank D. Wald for his review of the article, and an anonymous reviewer for helpful criticisms.
Published - 817.full.pdf