Collaborative Research: Investigating the role of dynamic strain fields in earthquake triggering processes by simulating full wavefield with 3D seismic velocity structures

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Observations of earthquakes caused by perturbations from other earthquakes, both close by and far away, are important for understanding how earthquakes happen and the mechanisms that trigger them. Triggered earthquakes caused by passing seismic waves suggest that earthquake processes are not completely random and independent on disconnected faults. For example, the 2002 Denali magnitude 7.9 earthquake in Alaska triggered abundant earthquakes in the western US. Why do earthquakes correlate with the passing seismic waves, and how do these tiny ground motions cause earthquakes? A better understanding of such processes will help our fundamental understanding of complex earthquake rupture processes and will aid in mitigating seismic hazards by accurately assessing where and when the next earthquake may occur. This project will take advantage of newly developed computational tools and characterizing the relationships between the patterns of the triggered earthquakes and the waves generated by distant earthquakes. The project will develop a new statistical approach to identify triggered earthquakes in southern California and the Caribbean region. The spatial and temporal evolutions of these triggering responses will be examined across multiple fault systems in these regions of interest. The project supports a collaboration between scientists at the University of California, San Diego and the University of Miami. Graduate students, undergraduate students, and postdoctoral fellows will all participate in the project. The work will be of broad interest to those who study earthquakes and their associated hazards. Major earthquakes frequently dynamically trigger seismic events at multiple disconnected faults up to thousands of kilometers away. The correlation between the passing seismic waves and triggered seismicity is robust yet puzzling. A key challenge in understanding dynamic triggering is comparatively characterizing the realistic dynamic strain fields at seismogenic depth and how the associated elevated seismicity evolves through time and space. This project aims to systematically model dynamic strain fields of earthquake sequences and their relation to dynamically triggered earthquakes within a framework of heterogeneous 3D seismic velocity media. The primary goal of the project is to investigate the time-dependent fault zone stress state and fault zone material properties. The project will first identify dynamic triggering cases in southern California and the Caribbean region by developing a new statistical approach that uses distributions of statistics instead of the statistics solely to find significant cases. The project will then simulate realistic dynamic strain fields of these cases with high-resolution 3D velocity models and the SPECFEM 3D algorithms. The project plans to develop a high-resolution body wave velocity model and earthquake catalogs for the Caribbean region. A central element of this work is using the spatiotemporal migration patterns of regional seismicity as tracers of the evolving stress state and material characteristics and cross-examining these patterns with characteristics of the full dynamic wavefields.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.