HR: 0800h
AN: T51D-1371    [Abstracts]
TI: Regional mapping of crustal structure in Southern California Using Receiver Functions
AU: * Yan, Z
EM: yanmei@gps.caltech.edu
AF: CALTECH, MC252-21, CALTECH, Pasadena, CA 91125
AU: Clayton, R W
EM: clay@gps.caltech.edu
AF: CALTECH, MC252-21, CALTECH, Pasadena, CA 91125
AB: Lateral variations of crustal structure in Southern California are determined from receiver function studies using data from about 175 broadband stations of the Southern California Seismic Network (SCSN) and LARSE surveys. The results include crustal thickness estimates at the stations themselves, and where possible, cross-sections are presented. Large rapid variations in the crustal structure are observed beneath the San Gabriel Mountains (SGM), which include a jump from a two-layered structure to a three-layered structure from east SGM to central SGM, and rapid deepening of the Moho depth from stations south of the San Gabriel fault to stations north of it and then the sudden shallowing further to the north near the San Andreas Fault (SAF). The differences in the subsurface crustal structures correlate with the surficial geological evidence that the stations sit on different allochthonous terranes. This correlation between the surficial geological data and subsurface geophysical data indicates that strong coupling exists between the upper crust and lower crust, and that crustal structure has preserved at least some of its original properties. A root where the Moho ramps in depth from neighboring 30-33 km to 36-39 km is imaged beneath the central portion of the SGM, which confirms the existence of a Mountain root beneath the SGM of Kohler and Davis (1997), but with more details provided here --- the root is not centered beneath the SAF, but two separate roots exist in this area, one is beneath the central SGM south of the SAF, a separate one locating to the north of the SAF, which is related to the uplift of the San Bernardino Mountains. A mid-crustal low-velocity zone at depths ~15-24 km is observed beneath some station groups in the SGM, which correlate with the `Bright Spot' imaged by Ryberg and Fuis (1998). Relatively small variation is observed in the western Mojave Desert, but a shallow Moho of about 23-27 km is observed in the eastern Mojave Desert and a sudden jump of about 8 km occurs beneath the Fenner Valley, east of Amboy, CA (station DAN) over a lateral distance of no more than 12 km. Unusual receiver functions, including Pms arrivals, are observed for some stations in the trans-tensional zones of Dokka's kinematical model (1995), such as the station beneath Barstow (RRX). This indicates that opening between different blocks and thus rotation of the blocks in this type of model might extend to the Moho. A low velocity zone just below the Moho is observed in several station groups in the Eastern Mojave Desert, which indicates that the sub-crustal mantle is unusually hot and probably partially melted there, correlating with the extension and frequent volcanic activities there. Asymmetric extension of Salton Sea is observed --- gradual thinning to the east, and sharp transition to the west. Crustal thickening and local variations are also observed beneath the southern Sierra Nevada and nearby central Basin and Ranges. Large rapid variations in the lower crustal structure and Moho depth are observed in several places, which indicate that the lower crust is strongly laterally heterogeneous in this region.
DE: 7205 Continental crust (1219)
DE: 7218 Lithosphere (1236)
DE: 8108 Continental tectonics: compressional
DE: 8109 Continental tectonics: extensional (0905)
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005