How rupture velocity variations modify earthquake source parameter estimations

Doron Morad, Shahar Gvirtzman, Yael Gil, Jay Fineberg, & Emily E. Brodsky

Submitted September 7, 2025, SCEC Contribution #14967, 2025 SCEC Annual Meeting Poster #TBD

Seismic waves remain the primary observational tool for probing the rupture dynamics of earthquakes. Source parameters such as seismic stress drop and seismic moment are typically inferred from the source time function derived from far-field ground motion recordings. These parameters are critical for understanding earthquake rupture processes and for informing risk and hazard assessments. However, their estimation depends on assumptions about the source and path effects—particularly the notion of a constant rupture velocity both within and across events—which are necessary due to the lack of direct access to the mechanical processes governing rupture.
A key challenge lies in determining how features in observed seismograms reflect underlying variations in rupture velocity along a fault. Spatial heterogeneities in rupture speed, whether arising from material contrasts, stress conditions, or imposed barriers, may leave identifiable signatures in far-field waveforms, yet the nature of these signatures remains poorly constrained. Establishing a systematic connection between fault heterogeneity and seismogram complexity could offer new insights into how rupture dynamics evolve. In particular, variations in rupture velocity can significantly alter the radiation pattern, frequency content, and apparent source properties of an event, potentially complicating interpretations of rupture size and stress drop.
To address these challenges, we conduct laboratory earthquake experiments in transparent, brittle materials (PMMA), which allow direct observation of the rupture process and surrounding strain field. Using high-speed imaging in combination with dense arrays of acoustic sensors or strain gauges, we are able to independently measure rupture characteristics while also applying seismological techniques to extract source parameters. This dual framework enables a controlled investigation into how rupture velocity variations and imposed barriers shape seismic waveforms.
Our results demonstrate that final event size is strongly dependent on rupture velocity, even in the presence of fracture energy barriers. Moreover, we find that the relationship between corner frequency and rupture size is nontrivial, as local variations in rupture speed introduce complexities that depart from classical scaling assumptions. These findings highlight the need to account for rupture heterogeneity in both experimental and field-based interpretations of earthquake source processes

Key Words
Earthquake seismologyRupture dynamicsEarthquake early warning, Laboratory earthquakes, Acoustic sensing

Citation
Morad, D., Gvirtzman, S., Gil, Y., Fineberg, J., & Brodsky, E. E. (2025, 09). How rupture velocity variations modify earthquake source parameter estimations. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)