HR: 0800h
AN: S41A-0249 [Abstracts]
TI: P-wave Tomographic Image Across the Central Transverse Ranges Region From Inversion of Local Earthquake and Active Source Data, Southern California
AU: * Li, L
EM: li.li@mail.uh.edu
AF: TGS-NOPEC Geophysical Co., 2500 Citywest Blvd, suite 2000, Houston, TX 77042, United
States
AU: * Li, L
EM: li.li@mail.uh.edu
AF: University of Houston, 4800 Calhoun Rd., SR1, Rm312, Houston, TX 77204, United States
AU: Zhou, H
EM: h.zhou@ttu.edu, hzhou@uh.edu
AF: University of Houston, 4800 Calhoun Rd., SR1, Rm312, Houston, TX 77204, United States
AU: Zhou, H
EM: h.zhou@ttu.edu, hzhou@uh.edu
AF: Texas Tech University, Dept of Geosciences, Lubbock, TX 79409, United States
AB:
The central Transverse Ranges region is considered as a place that has documented significant evidence of
tectonic history of southern California. To investigate such a region associated with extensive Cenozoic tectonic
activities, we apply a new deformable-layer tomography approach to determine layers of varying thickness as a
direct product of tomographic imaging. 1,546 P-wave first arrival data from local earthquakes and 10,869 from
active shots of Los Angles Regional Seismic Experiment (LARSE) I have been used together to invert the velocity
structure along a northeastern trending 2-D profile across the Central Transverse Ranges region. The combined
data result in highly dense ray path distribution, especially within the upper crust. In addition, Moho depths from
previous study have been incorporated into the inversion to improve solving the model in the deep and sparsely
sampled areas. The tomographic inversion procedure implemented in this study is as follows: first, a long
wavelength model is constructed by inverting local earthquake arrivals only with sparse Moho constraints;
second, this tomographic model is refined by adding surface seismic arrivals and introducing lateral velocity
variations within layers. Along the profile, our tomographic image shows high resolution, detailed near-surface
geological features besides those long-wavelength features resolved in the previous studies. The existence of
the San Andreas Fault is clearly evidenced, which is characterized by a vertical low-velocity zone to at least 20-km
depth. The sedimentary basin boundaries are observed unconformably lying above the high velocity basement.
Near the northern edge of the Los Angeles Basin and southern foothills of the San Gabriel Mountains in the upper
crust, the high velocity gradient units on two sides of this high velocity feature represent that the transition from
sedimentary rocks to crystalline rocks is abrupt, which could be indicative of the major basin-bounding faults,
such as the Whittier fault and the Sierra Madre fault zones. Our new tomographic image represented by both
layers and cells has provided new insights across the Central Transverse Ranges region, and the resolution of
the tomographic solution has been greatly improved by using local earthquake data and surface seismic data
jointly.
DE: 0935 Seismic methods (3025, 7294)
DE: 6982 Tomography and imaging (7270, 8180)
DE: 7270 Tomography (6982, 8180)
DE: 8180 Tomography (6982, 7270)
SC: Seismology [S]
MN: 2007 Fall Meeting