Bends and Ends of Surface Ruptures

Glenn P. Biasi, & Steven G. Wesnousky

Published October 10, 2017, SCEC Contribution #7056

We examine 67 surface rupture maps for map-scale complexities including fault bends, discon-tinuous rupture, overlaps, and fault-to-fault rupture. These structural properties of faults influ-ence the likelihood of rupture propagation and estimates of magnitude of future ruptures. Angles of bends ending surface rupture for strike slip ruptures are systematically larger than interior bends, while corresponding populations are similar for dip-slip events. The probability of pass-ing a bend in a strike slip rupture increases systematically with the bend angle in a relationship roughly summarized by the passing ratio PR = 3.0 – 0.077*A, where A is the bend angle. Bends of 26° are passed or stop rupture with about equal probability. Measurements of maximum inte-rior bend angles and net orientation change of rupture ends are consistent with predictions for frictional resistance in the presence of regional stress having approximately constant local orien-tation. Sums of absolute values of bends in rupture divided by rupture length give an average curvature. Strike-slip ruptures concentrate below 1°/km, with a maximum of 1.7°/km; dip slip curvatures are 3 times larger. Overlaps in dip slip ruptures consistently span a larger fraction of rupture length than strike slip ruptures, commonly expressed by secondary offsets of the hanging wall. We find that most fault-to-fault rupture connections jump to a fault of like mechanism. Only two strike-slip ruptures in the set jump to reverse structures and continue for a significant length. Results here have multiple applications for seismic hazard estimation and rupture dy-namic modeling.

Key Words
rupture geometry, fault hazard analysis

Citation
Biasi, G. P., & Wesnousky, S. G. (2017). Bends and Ends of Surface Ruptures. Bulletin of the Seismological Society of America, 107(6), 2543-2560. doi: 10.1785/0120160292.

Related Projects & Working Groups
Working Group on California Earthquake Probabilities