New Perspectives on Newport-Inglewood Fault Geometry

Natasha Toghramadjian, Andreas Plesch, Izabella Sabharwal, & John H. Shaw

Published August 14, 2020, SCEC Contribution #10610, 2020 SCEC Annual Meeting Poster #010 (PDF)

Poster Image: 
The Newport-Inglewood Fault is an active, right-lateral fault system that forms the southwestern edge of the Los Angeles Basin and passes through one of the most intensely urbanized regions of California. The southern portion of the fault ruptured in the 1933 Long Beach (Mw 6.4) earthquake, and the fault system poses high seismic hazard to the nearly 20 million people living in the greater metropolitan area. We revisit this urban fault and present holistic new perspectives on its 3D geometry to depth, with an initial focus on the Long Beach and Seal Beach segments.

Following the approach of Riesner et al. (2017), we integrate 2D and 3D seismic reflection surveys, robust stratigraphic controls from decades of oil industry well records, and hypocenter and focal mechanism catalogs recently expanded through template-matching (Yang et al., 2012, Ross et al., 2019). We generate 3D fault geometry via an objective and reproducible method that treats these data as weighted interpolation constraints. Our initial 3D fault models highlight the complexity of the fault geometry, which includes multiple splays and complex linkage patterns at depth. Some portions of this fault system appear to reactivate Miocene-age normal faults, which have been rotated into near-vertical geometries that are conducive to strike-slip motion in the present transpressional regime. Overall, these models show similar levels of complexity to recent strike-slip earthquake ruptures (e.g., the 2019 M6.4 and M7.1 Ridgecrest sequence, Plesch et al., 2020), which has important implications for seismic hazard assessment.

Citation
Toghramadjian, N., Plesch, A., Sabharwal, I., & Shaw, J. H. (2020, 08). New Perspectives on Newport-Inglewood Fault Geometry. Poster Presentation at 2020 SCEC Annual Meeting.


Related Projects & Working Groups
Earthquake Geology