Fault Displacement Hazard for Strike-Slip Faults

Abstract

In this paper we present a methodology, data, and regression equations for calculating the fault rupture hazard at sites near steeply dipping, strike-slip faults. We collected and digitized on-fault and off-fault displacement data for 9 global strike- slip earthquakes ranging from moment magnitude M 6.5 to M 7.6 and supplemented these with displacements from 13 global earthquakes compiled by Wesnousky (2008), who considers events up to M 7.9. Displacements on the primary fault fall off at the rupture ends and are often measured in meters, while displacements on secondary (off- fault) or distributed faults may measure a few centimeters up to more than a meter and decaywithdistancefromtherupture.Probabilityofearthquakeruptureislessthan15% for cells 200 m× 200 m and is less than 2% for 25 m× 25 m cells at distances greater than200mfromtheprimary-faultrupture.Therefore,thehazardforoff-faultrupturesis much lower than the hazard near the fault. Our data indicate that rupture displacements upto35cmcanbetriggeredonadjacentfaultsatdistancesoutto10kmormorefromthe primary-fault rupture. An example calculation shows that, for an active fault which has repeated large earthquakes every few hundred years, fault rupture hazard analysis should be an important consideration in the design of structures or lifelines that are located near the principal fault, within about 150 m of well-mapped active faults with a simple trace and within 300 m of faults with poorly defined or complex traces. Online Material: Description and tables of displacement data, distributed rup- tures, mapping accuracy, and regression statistics.