Where do faults go fast? Geometry of sub- and supershear ruptures
Alba M. Rodriguez PadillaSubmitted September 7, 2025, SCEC Contribution #14955, 2025 SCEC Annual Meeting Poster #TBD
Supershear rupture speeds are often linked to long, straight fault segments, but transitions from sub-Rayleigh to supershear speeds can also occur at geometrical complexities such as steps. Most evidence comes from single events, without comparison to subshear earthquakes, and teleseismic estimates of supershear locations can be uncertain by tens of kilometers. I present preliminary results from analysis of 39 continental surface rupturing strike-slip earthquakes, 13 of which reached supershear rupture speeds using simplified fault maps, distributed fracture maps, source time functions, and displacement data. Supershear segments are markedly smoother (lower RMS roughness) than subshear segments on the same events, which are themselves slightly smoother than faults where ruptures remained sub-Rayleigh. However, 30% of the supershear segments match subshear segments in length and roughness, indicating that geometry and length may be necessary but insufficient factors to facilitate the transition. Rougher (larger RMS roughness than typical subshear) segments often bound supershear segments. These rougher parts of the fault may seed the speed jump, which is then sustained by the long and straight segments. Supershear segments also show larger, more uniform slip, and less distributed fracturing, though the slip profiles themselves are undiagnostic of supershear. These early results offer clues to the mechanics of triggering and sustaining supershear in natural faults, and may help identify supershear-prone sections in continental strike-slip faults.
Key Words
supershear, rupture mechanics, surface ruptures
Citation
Rodriguez Padilla, A. M. (2025, 09). Where do faults go fast? Geometry of sub- and supershear ruptures. Poster Presentation at 2025 SCEC Annual Meeting.
Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)
