EAR-PF: Towards a robust understanding of the spatio-temporal evolution of foreshock sequences from the laboratory to the field

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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).Dr. David C. Bolton has been awarded an NSF EAR Postdoctoral Fellowship to investigate the evolution of earthquake foreshock sequences in time and space, explored through natural and laboratory fault zones. Estimating the timing and location of future earthquakes has been a long-standing goal in the study of seismology. However, progress in this area has been slow due to a poor understanding of the connections between the origins of earthquakes and seismic activity. Foreshocks are small earthquakes that precede the main earthquake and are thought to be indirect evidence that a fault is close to failure. However, foreshocks are not an easily observed feature of all earthquakes, and their connection to the impending earthquake is not well understood. This work will integrate laboratory and field-based observations of foreshocks with an aim to provide a coherent understanding of the evolution of foreshock sequences. A significant focus will be devoted to investigating whether foreshock properties encode information about the mainshock size. This work will provide key insights into the preparatory phase of earthquakes and will help advance earthquake early warning systems and improve earthquake hazard assessment. The project will also join forces with the GeoFORCE outreach program led by the Jackson School of Geosciences at UT-Austin to provide research opportunities to underrepresented communities in southwest Texas. This project will implement novel machine learning and earthquake seismology techniques for developing high-fidelity earthquake catalogs that are rich in small magnitude events. These high-resolution catalogs will illuminate how foreshocks interact with each other, their evolution in space and time, and their connection to the mainshock. The project will utilize laboratory experiments instrumented with acoustic emission monitoring to shed light on the causative processes that drive foreshock sequences. Fault zone properties such as stress, slip displacement, strain, will be integrated with the spatio-temporal patterns of acoustic emissions, allowing for a detailed understanding of the connection between the physics of earthquake nucleation processes and seismic activity. A second key element of the project will involve scaling up the laboratory observations to geologically relevant conditions by detecting and locating foreshocks on the well-characterized and seismically active Apennine fault system in Italy. This multi-scale, integrated research plan represents a unique opportunity to study seismic processes from the laboratory to tectonic scale and will determine if characteristics of laboratory foreshocks can be scaled up to tectonic fault zones. The proposed work has important implications for seismic hazard analysis and could help improve our ability to make accurate hazard forecasts and scientific predictions about earthquake processes.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.