How far will a rupture travel past a fault junction during a strike-slip event?

Sophia White, Alba M. Rodriguez Padilla, Vanessa Herrera, & Michael E. Oskin

Published September 11, 2022, SCEC Contribution #12489, 2022 SCEC Annual Meeting Poster #163

Surface ruptures pose a direct hazard to infrastructure and populations. Splay faults branch off of primary faults at acute angles. At these junctions, ruptures may propagate into the splay and continue for kilometers beyond the junction, allowing earthquakes to grow in magnitude by linking several faults. We use surface rupture maps of strike-slip events from the Fault Displacement Hazard Initiative (FDHI) database to investigate the mechanics of rupture propagation through fault junctions. We map splays for 31 strike-slip earthquakes. The splays were classified as breached or unbreached, depending on whether or not the earthquake propagated to the splay fault from the primary fault. We systematically measure the angle between each splay and the primary fault, and the distance the rupture traveled up the splay. Our results suggest that ruptures on breached splays typically do not travel further than 8 km beyond the junction, and ruptures halt less than a kilometer away from the junction in 65% of the cases. Occasionally, ruptures propagate further than 20 km past the junction. In these cases (5% of breached splays), the splay fault becomes the primary fault. Most of the breached splays are at angles < 30 degrees from the primary fault. A small portion (27%) of the ruptures breached splays with angles > 50 degrees. We do not find a correlation between the distance of rupture propagation and the angle at the splay junction. Our results are consistent with prior work showing angles < 20 degrees are typically breached, but we do not find a limiting angle that fully inhibits rupture propagation.

Key Words
splay, fault junction, strike slip, surface rupture

Citation
White, S., Rodriguez Padilla, A. M., Herrera, V., & Oskin, M. E. (2022, 09). How far will a rupture travel past a fault junction during a strike-slip event?. Poster Presentation at 2022 SCEC Annual Meeting.

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