SCEC Award Number 24014 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title Unraveling rupture propagation history from near-fault ground motion signatures: A mechanics-informed approach utilizing 3-D rupture models with fault zone complexity.
Investigator(s)
Name Organization
Ares Rosakis California Institute of Technology
SCEC Milestones D3-1, D3-2 SCEC Groups FARM, Seismology, GM
Report Due Date 03/15/2025 Date Report Submitted 04/02/2025
Project Abstract
 This study investigates the distinctive characteristics of ground motion signatures that differentiate supershear from subshear earthquake ruptures. Supershear ruptures, where propagation velocities exceed the surrounding rock’s shear wave speed, produce higher-frequency seismic waves resulting in intense energy pulses and more pronounced ground shaking. A hallmark feature of supershear ruptures is the formation of a shear Mach Cone at the rupture tip, leading to enhanced fault-parallel ground motion along the shock front—contrasting with the enhanced fault-normal motion observed in subshear rupture. This phenomenon has been documented in major earthquakes including the 2002 Denali, 2018 Palu, and 2023 Kahramanmaras event. Recent work by our group provided evidence for supershear propagation during the 2023 Kahramanmaras earthquake through analysis of strong ground motion records and dynamic rupture modeling, demonstrating correlation between rupture speed and fault-parallel motion enhancement. Despite substantial theoretical, numerical, and experimental evidence, debate persists regarding the reliability of fault parallel to fault-normal ground motion ratios as indicators of supershear rupture[12]. This research addresses the need for comprehensive frameworks that account for complex fault geometries and heterogeneous material properties to better constrain rupture propagation speed based on ground motion signatures.
Intellectual Merit We investigate how material heterogeneity affects ground motion signatures during earthquake ruptures. Using 3D dynamic rupture models, we discovered that sediment layers can cause local supershear propagation even when deeper rupture remains subshear, significantly altering ground motion characteristics. Unlike in homogeneous models, layered media showed that larger fault-normal than fault-parallel velocity doesn't rule out shallow supershear propagation. Sediment layers enhance fault-parallel velocity pulses during deep supershear propagation while increasing vertical ground motion in all scenarios. We identified a non-monotonic relationship between sediment properties and supershear transition. These findings underscore the importance of incorporating realistic subsurface heterogeneity in earthquake hazard assessment.
Broader Impacts This proposal partially funded one postdoctoral researcher, Dr. Mohamed Abdelmeguid, as part of his ongoing research on the role of fault zone complexity on ground motion characteristics. The research conducted as part of this proposal also engaged with other faculty members at Caltech, including Prof. Asimaki, on the role of ground motion variability on structural response, as part of a collaborative effort to understand the impact of fault zone complexity on ground motion. The research outcomes were presented at the 2023 SCEC annual meeting and were published in the Geophysical Journal International[
Project Participants The work done was conducted by Ares Rosakis and Mohamed Abdelmeguid at California Institute of Technology. We engaged in collaborations with Ahmed Elbanna at University of Illinois Urbana Champaign and Domniki Asimaki at California Institute of Technology.
Exemplary Figure Figure 1: The role of sediment layer contrast in altering rupture propagation and ground motion characteristics for Model A-1. (a) snapshots of the rupture propagation at different times (t = 2.5, 12.8, 18.0 and 23.1 s). (b) Contours of the fault-parallel and fault-normal particle velocity wave-field within near field of the fault at later stages of rupture propagation (t = 18.0 s, and t = 23.1 s). The fault-parallel velocity field shows the formation of a Mach cone structure at the free surface.
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