SCEC Award Number 24126 View PDF
Proposal Category Collaborative Research Project (Multiple Investigators / Institutions)
Proposal Title Dynamics of potential earthquakes on the Newport-Inglewood Fault
Investigator(s)
Name Organization
David Oglesby University of California, Riverside John Shaw Harvard University
SCEC Milestones C2-1, D3-2, A3-4, D1-1 SCEC Groups FARM, CEM, Seismology
Report Due Date 03/15/2025 Date Report Submitted 03/17/2025
Project Abstract
 The Newport-Inglewood fault (NIF) is located in the heart of the Los Angeles metropolitan area, posing a significant hazard to the communities it passes through and more broadly throughout Southern California. The 1933 M 6.4 Long Beach earthquake propagated northward along this fault, [Wood, 1933], and likely terminated at a complex, multi-segment restraining bend/stepover structure in the Signal Hill area [Hough and Graves, 2020]. An accurate estimate of seismic hazard in the region may depend on investigation of the earthquake potential of this geometrically complex feature. We use a high-resolution, data-constrained 3D fault model of the Long Beach restraining bend system of the Newport-Inglewood fault (NIF) [Toghramadjian and Shaw, 2024] as input for 3D dynamic rupture simulations using the mixed-flux discontinuous Galerkin code drdg3d [Zhang et al., 2023]. Our current models incorporate the Cherry Hill (CHF) and Northeast Flank (NEFF) fault segments, and we are implementing the other fault segments at this time. We vary our nucleation locations to determine how rupture directivity affects rupture branching behavior between the fault segments. We find that rupture propagation from southeast to northwest tends to produce significant slip on both the CHF and NEFF segments, uplifting the Signal Hill region, in agreement with geological evidence of slip on these structures. Rupture in the opposite direction on the NIF produces slip almost entirely bypassing the NEFF. The results may have implications for both the seismic hazard in the region and the dynamics of 3D branching faults in general.
SCEC Community Models Used Community Stress Model (CSM)
Usage Description We used the SCEC CSM to define our initial stress pattern for our faulting models.
Intellectual Merit The current results help to elucidate the earthquake potential of the Newport-Inglewood fault, and particularly its rupture pattern and near-surface behavior, which are critical for ground motion generation and surface offset and deformation. It also helps to explore the behavior of branched and offset fault systems that merge to simpler structures at depth. In particular, we show that approaching a branch from below, rather than simply along strike, can have important implications for slip partitioning between branches.
Broader Impacts This project illustrates how different groups in SCEC with complementary research specialties (in this case, fault structure and dynamic modeling) can combine forces to produce accurate models of faulting scenarios in California. The project has introduced three graduate students (one of whom is from a group traditionally underrepresented in science) to a new and very promising 3D dynamic modeling method, helping to develop their research skills.
Project Participants SCEC researchers David Oglesby (UCR), John Shaw (Harvard), and Andres Plesch (Harvard) have worked on this project, as well as graduate students Natasha Toghramadjian (Harvard), Lupita Bravo (UCR), and Adam Margolis (UCR).
Exemplary Figure Figure 3: Final slip from models with nucleation on the southeastern edge of the modeled CHF (a), center of the modeled CHF (b), and northwestern edge of the modeled CHF (c). Different nucleation locations produce different branching behaviors, leading to different slip partitioning between the faults.
Linked Publications

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