Earthquake Shaking Scales with Rupture Complexity

John E. Vidale, & Hao Zhang

Submitted September 7, 2025, SCEC Contribution #14849, 2025 SCEC Annual Meeting Poster #TBD

The high-frequency energy radiation efficiency of large earthquakes plays a critical role in determining their destructiveness. The efficiency varies by more than an order of magnitude, yet the underlying controlling factors remain poorly understood. Here, we demonstrate that high-frequency (0.5 to
2 Hz) energy radiation in large earthquakes correlates with the spatial complexity of their rupture processes.

We work on three fronts: First, we define a fractal measure of rupture complexity that is based on the effective width of the aftershock zone as a function of scale, applied without free parameters. Second, a model of fault complexity built from a power law density of secondary faults is constructed and calibrated against the complexity measure. Third, the measure is applied to 15 globally distributed magnitude 6 to 8, shallow, continental earthquakes with accurately located aftershocks. Scales considered range from about 4 to 15 km, and aftershock zone widths are about a km. For the two best-studied events, we can also resolve that high frequency radiation is strongest at the spots along the rupture showing the most complexity.

We find that greater rupture complexity produces higher energy radiation efficiency. The high-frequency energy to moment ratios vary by about a factor of 10 with a correlation coefficient of 0.62 and a highly significant p value of 0.007. In our model, the measured rupture complexity corresponds to a fractal subfault size-frequency distribution. We can also track the increasing complexity of the illuminated fault system with time into the aftershock sequence. Our findings highlight new ways of surveying an earthquake rupture, specifically the improvement from incorporating rupture complexity beyond simple planar fault models when modeling energy radiation. With a better understanding of energy radiation efficiency during faulting, seismic hazard estimation may be improved.

Key Words
earthquake, rupture, complexity, seismology

Citation
Vidale, J. E., & Zhang, H. (2025, 09). Earthquake Shaking Scales with Rupture Complexity. Poster Presentation at 2025 SCEC Annual Meeting.

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