Historic Surface Rupture Observations Confirm Relationship Between Curved Slickenlines and the Direction of Rupture Propagation
Abstract
Temporal changes in slip direction are common during large-magnitude earthquakes. Such changes are preserved as curved slickenlines on fault surfaces. Spudich et al. (1998, BSSA) used the curvature of slickenlines found on the Nojima fault following the Mw 7.2 Kobe earthquake to infer the magnitude of shear traction on the fault surface. However, aside from this pioneering work, the potential link between curved slickenlines and the dynamics of earthquake rupture has received little attention. During field reconnaissance following the Mw 7.8 Kaikōura earthquake (South Island, New Zealand), we observed curved striae up to 6 m long on freshly-formed free faces of the Kekerengu fault. Using simulations of spontaneous dynamic rupture on a vertical strike-slip fault, we show that temporal changes in rake are driven by vertical stresses along mixed-mode rupture directions produced within the so-called cohesive zone. We demonstrate that slip-path convexity is sensitive to the direction of rupture propagation (Kearse et al., 2019, Geology). Our hypothesis is consistent with the curvature of slickenlines on both the Kekerengu and Nojima faults, and the known rupture direction during those events. If our theory is proven to be robust, it will provide a tool for earthquake geologists to extract the rupture direction of paleo strike-slip earthquakes.
Here we test our hypothesis against all available geological data (both historic and contemporary) that document changes in slip direction during a surface-rupturing earthquake. We incorporate events such as the Mw 7.9 Wenchuan, Mw 6.6 Fukushima, and Mw 7.1 Ridgecrest earthquakes. To investigate the relationship between slip path convexity and the direction of rupture propagation, we also require mainshock hypocentres for each event, which restricts our analysis to the instrumental period. By expanding our previous simulations to include dip-slip earthquakes, we show that slip path convexity at the free surface during dynamic rupture is sensitive to the rupture propagation direction for all faulting mechanisms. We find that this generalized hypothesis is supported by the available geological and seismological data, providing necessary validation for earthquakes geologists seeking to constrain paleo rupture direction from geological observations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T12B..04K
- Keywords:
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- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITY;
- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 7221 Paleoseismology;
- SEISMOLOGY;
- 7290 Computational seismology;
- SEISMOLOGY