SCEC Award Number 24172 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title Seismic Signals Preceding and Accompanying Large Earthquakes in Laboratory Experiments
Investigator(s)
Name Organization
Emily Brodsky University of California, Santa Cruz Doron Morad University of California, Santa Cruz
SCEC Milestones D2-2, C3-1 SCEC Groups FARM, EFP, Seismology
Report Due Date 03/15/2025 Date Report Submitted 03/17/2025
Project Abstract
 How do earthquakes begin and what information about this process is contained in a far field seismogram? We present a quantitative analysis of laboratory earthquakes incorporating both laboratory-scale seismic measurements coupled with high-speed imaging of the controlled dynamic ruptures that generated them. We generated variations in the rupture properties by imposing sequences of controlled artificial barriers along the laboratory fault. We first demonstrate that direct measurements of imaged slip events correspond to established seismic analysis of acoustic signals; the seismograms correctly record the rupture moments and maximum moment rates. We then investigate the ruptures’ early growth by comparing their measured seismogram velocities to their final size. Due to higher initial elastic energies imposed prior to nucleation, larger events accelerate more rapidly at the rupture onset. We find that the corresponding seismogram velocities are therefore predictive of the final rupture size. This observation holds in the presence of barriers with one notable exception. Rupture events that overtake a previously arrested rupture are less magnitude predictable, likely because of the stress heterogeneity (and resulting stored elastic energy) induced by the earlier event. For all other events, the higher elastic energy at nucleation results in faster and larger ruptures, and hence the initial seismogram velocity and ultimate size correlate well. This degree of magnitude predictability is consistent with some, but not all recent natural observations. For early warning purposes, we suggest that confining the observational database to the conditions most conducive to magnitude predictability may provide stronger correlations.
Intellectual Merit We present the first comparison between seismically inferred source parameters and direct imaging of rupture in a laboratory experiment. The seismic and imagery-based measurements agree. The seismically measured moment release rate at a very early stage during the rupture process, before the rupture is disturbed by a barrier, can statistically predict the ultimate magnitude. A clear exception is when events have high stress pockets due to prior events, and those events will usually release their moment in the same fashion as the previous event. Thus, this work explains where early seismograms are predictive of magnitude and where they are not.
Broader Impacts This project: (1) supported the development of an early career researcher, Doron Morad, (2) directly impacts our ability to execute early warning successfully by delineating the circumstances and which it will, and won't, work.
Project Participants Doron Morad, Postdoctoral Scholar
Jasen Bradford, Undergraduate Research Assistant
Jay Fineberg, Hebrew University
Shahar Gvirtzman, Hebrew University
Exemplary Figure Figure 1: Seismogram displacement vs. time. The data are logarithmically color-coded by the maximum seismogram displacement achieved by each seismogram.
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