New Perspectives on Newport-Inglewood Fault Geometry
Session: How Should Low-Probability Earthquakes be Considered in Hazard Assessments?
Type: Oral
Date: 4/23/2021
Presentation Time: 10:15 AM Pacific
Description:
As illustrated by the 2019 Ridgecrest earthquake sequence, the instrumental and computational capabilities that define seismology today enable us to capture the geometric and kinematic complexity of seismogenic fault systems and their rupture processes with increasing precision.
The Newport-Inglewood fault, however, has not had a comparable event in the modern seismic period—and thus aspects of its subsurface geometry and seismogenic potential remain poorly understood. This tectonically active right-lateral system extends for more than 40 km across the Los Angeles basin, California, and last ruptured in the 1933 Mw 6.4 Long Beach earthquake. The fault poses significant seismic hazard to the nearly 20 million people living in the greater Los Angeles metropolitan area.
We generate 3D models of the Newport-Inglewood fault’s subsurface geometry by leveraging numerous diverse, independent data sets—the best alternative in the absence of data from a recent large earthquake. 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) to characterize the subsurface geometry of the fault. To develop 3D fault representations, we follow the objective and reproducible method of Riesner et al. (2017), treating 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 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 Ridgecrest sequence, Plesch et al., 2020), which has important implications for seismic hazard assessment.
Presenting Author: Natasha Toghramadjian
Student Presenter: Yes
Authors
Natasha Toghramadjian Presenting Author Corresponding Author natasha_toghramadjian@g.harvard.edu Harvard University |
John Shaw shaw@eps.harvard.edu Harvard University |
Andreas Plesch plesch@fas.harvard.edu Harvard University |
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New Perspectives on Newport-Inglewood Fault Geometry
Session
General Session