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Unearthing Slickenlines on the 2016 Rupture of the Kekerengu Fault and Paleosurface Ruptures of the Alpine Fault, New Zealand: Testing the Veracity and Utility of the Rupture-propagation-direction / Curved-slickenline Hypothesis

Description: 

Earthquake rupture direction is known to influence the distribution of strong ground shaking in large earthquakes. A recent theory put forward by Kearse et al. (2019; Geology v 49, n 9) - based on spontaneous dynamic rupture modelling and grounded in geological field observations - links patterns of curvature of slip striations (slickenlines) on fault surfaces to the direction of rupture propagation. We test this theory by un-earthing slickenlines on a fault (the dextral Kekerengu Fault) that had a known rupture propagation direction (northeastward) during the 2016 Kaikōura earthquake, New Zealand. Slickenlines that were exhumed from 1-4 m below the ground surface record the same sense of convexity as those observed on surface scarps immediately following the 2016 rupture. The slickenlines had a convex-up sense of convexity when viewed looking southeast onto the northwest-facing fault plane. This indicates a northeastwardly propagating rupture.

On the Alpine Fault, the dominant structure in New Zealand’s ∼30 mm/yr continental transform plate boundary, we observed on natural and hand-excavated exposures of the fault plane many curved slickenlines that formed during paleosurface ruptures. These were studied at three sites that span a region known to variably halt or allow passage of past earthquakes (an “earthquake gate”). Our field data reveal directions of paleo rupture propagation that complement and enhance the fault’s spatiotemporally rich paleoseismic record. At Hokuri Creek and Martyr River, we observed both convex-up and convex-down curved slickenlines on and adjacent to principal slip surfaces, indicating past ruptures from both northeast and southwest of the proposed “earthquake gate”. At Martyr River, relationships suggest that the most recent event (inferred to correlate to 1717 CE) ruptured from the southwest. Our results both here, and on the Kekerengu Fault, demonstrate the utility of curved slickenlines as a valuable new paleoseismological tool for determining past rupture directions, applicable to surface-rupturing faults globally.
 

Session: The Landscape Record of Earthquakes and Faulting - II

Type: Oral

Date: 4/16/2025

Presentation Time: 11:15 AM (local time)

Presenting Author: Russ

Student Presenter: No

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