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Developing a Near-fault Non-ergodic Ground Motion Model for the Ridgecrest, CA, Area

Description: 

One major obstacle in earthquake research is the lack of near-fault recordings (<10 km). Abundant near-fault recordings could provide important new information about the physics of earthquakes and generation of ground motion at very short distances. In the current ground motion models (GMM), the near-fault motions (and hazards) are extrapolated from the data recorded at moderate and large distances assuming a linear behavior, which is not necessarily correct. However, near-fault seismic motions are crucial for resilience of near-fault structures, as they impose the most severe hazards due to the strongest shaking and possible significant displacement.

Starting at ~8 days following the M7.1 Ridgecrest, CA, earthquake, 15 1D or 2D dense arrays (461 sites) were deployed in the area of the rupture zone, which include four 1D arrays deployed across the surface rupture of the mainshock. The dense arrays recorded continuously for ~30 days and captured numerous aftershocks between magnitude 0 and 5.2. The majority of recordings have epicentral distances smaller than 20 km, with the smallest distance being ~0.1 km, which make it an unprecedented dataset for studying near-fault ground motions. In this work, we first compute FAS and PSA from aftershocks listed in a relocated earthquake catalog, after removing signals from overlapping aftershocks and anthropogenic noise. Next, we combine the dense array ground motion dataset with a regional Ridgecrest ground motion dataset and develop a non-ergodic GMM. Then, we investigate several aspects of the near-fault ground motions that are caused by source, site or path effects. Our current main findings include: 1) much weaker energy radiation at short periods from the shallowest part of the fault zone; 2) significant variations in site responses within the fault zone in both fault-normal and fault-parallel directions; 3) strong amplifications of ground motions within the fault zone by trapped waves and other damage zone waves; 4) evident changes of radiation patterns at short and long periods.

Session: Recent Advances in Modeling Near-source Ground Motions for Seismic Hazard Applications - I

Type: Oral

Date: 4/16/2025

Presentation Time: 08:45 AM (local time)

Presenting Author: Xiaofeng

Student Presenter: No

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