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Earthquake rupture through a step-over fault system: A case study of the Leech River Fault, southern Vancouver Island
  • Ge Li,
  • Yajing Liu
Ge Li
McGill University, McGill University, McGill University, McGill University

Corresponding Author:ge.li2@mail.mcgill.ca

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Yajing Liu
McGill University, McGill University, McGill University, McGill University
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The Leech River fault (LRF) zone located on the southern Vancouver Island can be interpreted as an extensional step-over system based on geological mapping and microseismicity relocation. It consists of two sub-parallel right-lateral active fault structures: the primary NNE dipping LRF structure to the north, and a secondary sub-vertical structure to the south, possibly an extension of the Southern Whidbey Island fault (SWIF). The possibility of an earthquake rupture nucleated on the LRF jumping across the step-over and continuing propagation on the SWIF has significant implications for seismic hazard of the populated southern Vancouver area. To study earthquake rupture jumping scenarios across the LRF system, we develop a finite-element model to simulate dynamic ruptures governed by a linear slip-weakening frictional law. The stress perturbations radiated from the LRF rupture will induce an Over Stressed Zone (OSZ, where shear stress exceeds static frictional strength) on the SWIF. With the increase of the OSZ size R_e, rupture develops from stopping on LRF (no jumping), to breaking part of the SWIF (self-arresting) or the entire SWIF (break-away). We demonstrate that rupture jumping scenario is a collective result depending on a range of parameters. Target parameters in our study include fault initial stress level, step-over offset distance and fault burial depth. We find that R_e and the receiver fault stress status are the keystone variables directly controlling rupture jumping scenarios, while other parameters exert their influence by resulting in different R_e.
Nov 2020Published in Journal of Geophysical Research: Solid Earth volume 125 issue 11. 10.1029/2020JB020059