SCEC Award Number 15205 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Empirical Data and Models Supporting Implementation of Complex Ruptures in the Broadband Platform
Investigator(s)
Name Organization
Glenn Biasi University of Nevada, Reno John Anderson University of Nevada, Reno
Other Participants
SCEC Priorities 3c, 6b SCEC Groups WGCEP, GMP, EFP
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
 We examine 75 surface rupture maps assembled by Biasi and Wesnousky (in press) for map-scale complexities including fault bends, ends, large steps, overlaps, and fault-to-fault rupture. By comparing maximum interior bends of ruptures to bends stopping ruptures at ends we derive a new empirical distribution expressing the probability that rupture passes a bend of a given angle. Bends of 18° are equally likely to be passed or to stop rupture, 13° are passed by 4:1, and at 27° stop rupture by a 4:1 margin. This relationship has applications in PSHA and to inform dynamic and kinematic rupture models. We also developed empirical data for two parameters used in UCERF3 that affect the probability of rupture propagation, the total absolute angular deflection (TAAD, or “squirrelyness”) and the net angular deflection (NAD) of rupture ends. Both measures are larger for dip-slip than strike-slip ruptures. Among strike-slip cases, NAD did not exceed 42° except for a few cases where rupture transitioned and continued on an oblique reverse or normal fault. TAAD is ≤235° for all ruptures, and ≤180° for strike-slip ruptures, compared to a limit of 560° in UCERF3. TAAD may be better parameterized by angular deflection per km of rupture. NAD of regional scale ruptures, including disconnected dip-slip cases, is generally well explained by a single or slightly varying stress direction. Ground motion consequences of fault bends and energy partitioning emerge from this study as recommended priorities for future work.
Intellectual Merit Empirical measurements of rupture complexity provide a data basis for evaluating models of rupture propagation and seismic radiation. We developed the first empirical relation for the relative ability of fault bends to stop rupture as a function of bend angle. We find that net angular deviation of regional scale ruptures can be explained by a semi-constant stress direction. Results support improved PSHA.
Broader Impacts New empirical data and relationships will improve the PSHA research and applications by SCEC and by practitioners who follow SCEC research. Improved seismic hazard models benefit society at large by informing expectations and supporting improved preparedness.
Exemplary Figure Figure 5, Comparison of passed interior bends to bends that stop ruptures. (Upper) The distributions of interior and ending bends are similar for dip slip but distinct for strike slip, and can be used. (Lower) Stopping effectiveness of bends is the ratio of fractions passing bends to fraction that stop rupture. Bends of 18 degrees are equally likely to stop or be passed in strike-slip rupture. Figure by authors.