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[S13-5-06] Slip-weakening distance and strength drop inferred from near-fault deformation during the 2016 M7.8 Kaikoura earthquake
The 2016 M7.8 Kaikoura (New Zealand) earthquake struck the east coast of the northern South Island, resulting in large surface offsets (>10 m), numerous landslides, extreme surface ground motions (over 1g), a regional tsunami, and large-scale slow slip events on the Hikurangi subduction interface. Since the earthquake was well recorded by GeoNet strong motion and GPS networks, near-fault ground motion may provide direct measurements of dynamic parameters associated with the fault-weakening process. Here we estimate a proxy of slip-weakening distance Dc'', defined as double the fault-parallel displacement at the time of peak ground velocity, from accelerograms recorded at near-fault stations. Three-component ground displacements were recovered from the double numerical integration of accelerograms, and the corresponding static displacements are validated against those derived from InSAR data. We estimate Dc'' of about 5 m at KEKS station located at 2.7 km from a segment of the Kekerengu fault where a surface offset of more than 10 m has been found. The inferred Dc'' is the largest value ever estimated from near-fault strong motion data, yet appears to follow the scaling of Dc'' with final slip reported in previous studies. The corresponding slip-weakening distance Dc and strength drop on the same fault segment may be validated against dynamic rupture simulations.