Characterizing seismic radiation from finite earthquake sources and links to fault physics

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

Scientists use measurements of shaking produced by earthquakes to understand the physics of underlying earthquake sources and to mitigate related hazards. Observations suggest that the total amount and properties of the energy carried by seismic waves may systematically differ for earthquakes produced in different fault settings, such as for large earthquakes occurring on subduction zone faults, like in Japan and Alaska, or major continental faults, like the San Andreas Fault in California. Dr. Lambert and his students will use physics-based computational models of earthquakes in an effort to explain these differences. They will investigate how different physical properties of faults and earthquake ruptures affect the resulting seismic waves, and conversely, how recordings of earthquake ground motions may be used to infer properties of the earthquake fault zone and the rupture. The research findings will help scientists estimate shaking from future great earthquakes, which is vitally important for earthquake hazard assessment and improvement of seismic building codes. This project provides support and training for an early-career scientist and several undergraduate and graduate students. The energy radiated from earthquake sources as seismic waves is a crucial parameter in earthquake physics and a direct input for the resulting strong ground shaking highly relevant to seismic hazard assessment. Observations suggest that, for a given size of the earthquake source, the total amount of radiated energy may systematically differ for earthquakes in different tectonic settings, such as subduction megathrusts and continental transform faults. The frequency content of seismic radiation is also inferred to systematically vary with source depth, with stronger higher frequencies originating from greater depths. Such differences in the amount and attributes of radiated energy between different fault regions raise questions about potential systematic differences in fault conditions and driving physics of large earthquakes, as well as scaling relationships used to estimate shaking, particularly if such scalings differ between tectonic settings. This project aims to improve our understanding of large earthquake scenarios in different tectonic plate boundary settings by developing physics-based computational models that reproduce a range of geophysical observations. The team will use these simulations to (1) examine what attributes of the resulting earthquake seismic radiation may discriminate between physical models of major faults; (2) characterize fundamental ingredients that affect seismic radiation, particularly those that generate high-frequency ground motions; and (3) develop plausible earthquake scenarios and corresponding seismic radiation inputs for strong ground motions. The simulated earthquake sources will serve as research tools representing 'ground truth' to explore discrepancies between the actual source properties determined directly from the simulations, and estimates derived from applying traditional observational techniques. This will allow a better understanding of how seismic signatures relate to the properties and behavior along natural faults and how to design optimal observational arrays to resolve important aspects of the earthquake source process. 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.