Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

I N T R O D U C T I O N The Alpine Fault is an 850 km-long dextral continental transform fault that accommodates up to 80% of current motion between the Pacific and Australian plates in the South lsland of New Zealand (e.g. Dements et al., 1994; Wallace et al., 2007; Fig. 1). The fault currently has one of the most spatiotemporally complete paleoearthquake records in the world with the timing and extents of the last 20 surface-rupturing earthquakes constrained over a 300 km length of the fault over the last 4 kyr (Howarth et al., 2021). Notably this record reveals an "earthquake gate" at or near the boundary between the Central and South Westland sections of the fault; over the last 4 kyr 55% of the surface ruptures are stopped at this gate as "single-section" ~Mw 7.5 earthquakes and 45% pass through the gate to become "multi-section" ~Mw 8.0 earthquakes including the three most recent paleoearthquakes (Howarth et al., 2021). Fig. 1: (A) Simplified active tectonic map of the South Island of New Zealand with Alpine Fault in red. (B) Model relating sense of slickenline curvature (convex-up, convex-down) to hypocenter and rupture propagation direction for a dextral fault. The same reference frame and color scheme are used for observations in the bottom panel.(C) Summary of the number and sense of convexity of curved slickenlines on principal slip surfaces observed in this study and paleoearthquake record spanning the earthquake gate.