NSF-BSF: Laboratory seismograms that provide insight into seismological observables

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

This is a project jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF-GEO) and the Israel Binational Science Foundation (BSF) in accord with the language in the Memorandum of Understanding between the NSF and the BSF. This Agreement allows a single collaborative proposal, involving US and Israeli investigators, to be submitted and peer-reviewed by NSF. Upon successful results of the NSF merit review and recommendation by the cognizant NSF Program of an award, each Agency funds the proportion of the budget and the investigators associated with its own country. The study of seismic waves is the most commonly used tool to investigate the mechanics of earthquakes. Earthquakes are described by parameters such as the seismic stress drop, seismic moment and radiated energy that are typically derived through the analysis of seismograms at great distances from the earthquake. These measurements play a crucial role in understanding the earthquake rupture process, risk and hazard assessments. However, they all rely on fundamental assumptions associated with the earthquake process and seismic wave travel which are necessary in the absence of any more direct information about the mechanical processes involved in earthquake rupture. Our understanding of earthquake rupture dynamics is based largely on seismic measurements and corresponding estimations of these parameters. Here we propose a series of experiments to directly measure fault rupture dynamics on the interface at the same time as taking seismic data in the laboratory. This project uses one of the only apparati in the world capable of the high-speed imaging required and combine that data with in-situ seismograms to develop a unique capability that can test and extend the uses of seismology for studying earthquakes. This project will foster an international collaboration with Hebrew University, building ties and intellectual exchange between scientists studying earthquakes on two of the highest risk and analogous systems on Earth: The Dead Sea Fault and the San Andreas Fault. This project focuses on a quantitative analysis of Acoustic Emission (AE) signals, which is a laboratory-scale counterpart to seismic measurements, coupled with direct and real-time dynamic rupture measurements derived from high-speed imaging in one of the only laboratories in the world capable of such measurements. This data will be used to address three major targets of observational seismology: magnitude predictability, rupture velocity and its covariance with earthquake size, and radiated energy. Providing a stronger foundation for interpreting these fundamental features of seismograms will allow more information to be gained from the seismological wavefield. The projec tinvestigates three targets and associated ongoing questions related to earthquake source parameters estimations: (1) Magnitude predictability: How early in the nucleation phase of an ideal fault surface can we estimate the size of a rupture? How is the likelihood of having a large magnitude earthquake affected by the presence of barriers? (2) Rupture velocity and its covariance with rupture size: Can observed seismograms be related to the rupture velocity profile? How does the variation in rupture velocities correlate with the final size of the rupture? (3) Radiated energy: Can the common range of scaled radiated energy for observed earthquakes be reproduced in the lab by using specific distributions or densities of barriers? Thus, can the ability to interpret natural observations of radiated energy be increased to infer fault asperity distributions, which in turn have implications for magnitude distributions? 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.