SCEC Award Number 25250 View PDF
Proposal Category Collaborative Research Project (Multiple Investigators / Institutions)
Proposal Title Investigating Near-fault Ground Motions with Dense Arrays
Investigator(s)
Name Organization
Xiaofeng Meng University of Southern California Camilo Ignacio Pinilla Ramos University of Southern California Yehuda Ben-Zion University of Southern California
SCEC Milestones D3-3, B2-1 SCEC Groups GM, Seismology
Report Due Date 03/15/2026 Date Report Submitted 03/25/2026
Project Abstract
 Following the Mw7.1 Ridgecrest, CA, earthquake, 15 dense 1D and 2D arrays (461 sites) were deployed around the main ruptures, including four 1D arrays across the surface rupture of the mainshock. The dense arrays captured numerous aftershocks with magnitudes in the range 0-5.2 within 10 km, and provided an unprecedented dataset for studying near-fault ground motions, which are crucial for near-fault hazards as they impose the strongest shaking and possible permanent displacements. However, In the current ground motion models (GMM), the near-fault motions are extrapolated from data recorded at moderate and large distances, assuming linear behavior which is not necessarily correct. Here, we combine the near-fault ground motion dataset from the Ridgecrest area with a regional dataset to develop a non-ergodic GMM. The developed GMM is used to investigate several aspects of the near-fault ground motions involving source, site, and path effects. Our initial findings include: 1) weak high-frequency energy radiation for shallow events; 2) significant variations in site responses within and around the fault zone in both fault-normal and fault-parallel directions; 3) strong frequency-dependent amplifications of ground motions within the fault zone. We propose to further analyze our near-fault GMM to constrain the effects of the damage zone, compare path effects between small and large events, investigate the near-fault saturation of ground motion, and compare our GMM to the regional GMMs.
Intellectual Merit Near-fault ground motions produce the most severe seismic hazards, due to the strongest shaking, significant displacement, and pulse-like accelerations. However, in the current ground motion models (GMM), the lack of near-fault data, especially from large earthquakes, is a serious shortcoming. In GMMs, the near-fault ground motions are often extrapolated from the data recorded at moderate and large distances assuming linear behavior. Here we seek to systematically study the near-fault ground motions around the Ridgecrest mainshock rupture zone, by developing a partially non-ergodic near-fault GMM. The developed GMM decomposes the ground motion variations into the repeatable source, site, and path effects.
Broader Impacts We develop a near-fault non-ergodic GMM based on small earthquakes and dense arrays data, which shed light on several scientific and engineering problems related to earthquake physics, fault zone properties, and seismic hazard. In particular, our study indicates that the variability in near-fault ground motions cannot be extrapolated from global GMMs and underscores the importance of exercising caution when modeling ground motion near active fault zones, where the spatial correlation is very short. Local non-ergodic GMMs are crucial for improving both the median predictions and uncertainty in near-fault ground motion modeling.
Project Participants Xiaofeng Meng, Camilo Ignacio Pinilla Ramos, Yehuda Ben-Zion
Exemplary Figure Figure 2. (a) δS2S (red lines) and δWS (blue lines) from EAS versus distance to fault strike for arrays B1-B4 at 0.05s. The gray dashed line denotes the approximate location where the array intersects the surface ruptures. The horizontal green and red bars denote the low velocity zone and its inner core identified by Qiu et al., (2021), respectively. (b-e) Same figures with panel (a) at 0.1 s, 0.2 s, 0.5 s, and 1 s period, respectively. (f) The VS30 values along arrays B1-B4. (g1-g4) The cross-section of VP/VS from the 3D velocity model beneath arrays B1-B4.
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