Collaborative Research: Roles of rupture complexity, geological structure, stress interaction on earthquake sequences

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Earthquakes remain one of the most significant natural hazards facing society. With the increase of human-induced seismicity, regions that previously had lower seismic risk (e.g., central United States) are now facing earthquake-related hazards. The dramatic increase in the seismicity rate during the past decade in central US, and the improved instrumentation here and in California provide a rich dataset of well-recorded small-to-moderate sized earthquakes in two very different geologic settings; one dominated by tectonic motion on the great San Andreas fault, and the other where human activities induced earthquakes on less continuous, smaller, faults. This provides the opportunity to learn more about the controlling factors and consequences of earthquakes in both settings. By studying and comparing the earthquakes and their interactions in two very differently deforming regions (Northern California and Oklahoma), this project will advance our understanding of the fundamental processes of earthquake physics, their dependence on tectonic setting, and help reduce earthquake related hazards. An improvement in understanding of the relationship between earthquake rupture processes and hazard parameters (seismicity and ground motion) could help to reduce seismic hazard posed to local communities and important infrastructure. This analysis will also combine earthquake and industry 3D seismic data, which will help to develop guidelines to identify potentially hazardous critically stressed faults in Oklahoma. The project includes mentoring and collaboration on a range of levels, contributing to the education of two graduate students (at OU) and support for an early-career PI (at OU). The derived state-of-the-art database of earthquake catalog, cluster characteristics and source parameters will provide fundamental input for many studies, and will be of broad interest to earthquake hazard community, and understanding of earthquake physics. The methods and workflow will feed into activities for classes in earthquake and exploration seismology, and structural geology. The complexity of earthquakes is a significant factor governing earthquake source dynamics and the consequent ground motions, and it is related to complexity in the fault structures on which the earthquakes occur. This project will use both high-quality earthquake seismograms and industrial 3D seismic data, and develop improved techniques to quantify complexity and enhance our understanding of the fundamental earthquake source process on a variety of temporal and spatial scales. The researchers focus on the inherent earthquake source variability, its relationship with geologic structure, and its influence on earthquake sequence evolution and ground motion patterns. They perform a combined spectral and time domain analysis of earthquake sources and geological fault structure in two distinct tectonic settings: northern California which is dominated by the San Andreas plate-boundary fault, and Oklahoma where human activities are inducing earthquakes in a low-strain rate region. Spectral complexity and source-time-function complexity will be quantified, and automatic classification methods will be developed to identify complex earthquakes. Collocated high-resolution industrial 3D seismic data and seismicity enables us to better understand characteristics of seismogenic faults in the basement in detail. The synthesis and integration of multiple datasets will help to understand the interlink between geologic structure and earthquake rupture.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.