We image the San Jacinto fault zone at Blackburn Saddle using earthquake waveforms recorded by a ~ 2-km across-fault linear array with 108 three-component sensors separated by ~ 10–30 m. The length and spatiotemporal sampling of the array allow us to derive high-resolution information on the internal fault zone structure with spatial extent that can be merged with regional tomography models. Across-fault variations in polarization, amplitude, and arrival time of teleseismic P waves indicate abrupt changes in subsurface structure near the surface trace of the fault (sensor BS55) and ~ 270 m to the northeast (sensor BS34). Analysis of fault zone head waves from local events reveals the existence of a deep bimaterial interface that extends from the array to at least 50 km southeast and has a section with > 10% velocity contrast. This analysis also corroborates the teleseismic results and indicates a broad damage zone primarily northeast of the fault bounded by a shallow bimaterial interface near BS34 that merges with the deep interface. Detection and waveform inversions of Love-type fault zone trapped waves generated by local events indicate a trapping structure within the broader damage zone with width of ~ 150 m, velocity reduction of ~ 55% from the surrounding rock and depth extent of ~ 2 km. The performed analyses provide consistent results on the subsurface location of the main seismogenic fault and properties of a major bimaterial interface and damage structure. The imaged fault zone properties are consistent with preferred propagation direction of earthquake ruptures in the area to the northwest.
Bibliographical noteKAUST Repository Item: Exported on 2021-03-10
Acknowledged KAUST grant number(s): OCRF-2014-CRG3-2300
Acknowledgements: We thank Marianne Karplus and Jerry Schuster for providing geophones for the experiment, and Hsin-Hua Huang, Elizabeth Berg, Yadong Wang, Scott Palmer, Kathleen Ritterbush, Jon Gonzalez, Jerry Schuster, Robert Zinke and Cooper W. Harris for assistance during the array deployment. The research was supported by the King Abdullah University of Science and Technology (Award OCRF-2014-CRG3-2300), the National Science Foundation (Grants CyberSEES-1442665 and EAR-1620601), and the Department of Energy (Awards DESC0016520 and DE-SC0016527). The data collected with the BS array are stored at the University of Utah Seismograph Stations and are available upon request. Most maps are made using the Generic Mapping Tools (Wessel et al. 2013). The manuscript benefitted from useful comments by two anonymous referees.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.
ASJC Scopus subject areas
- Geochemistry and Petrology