资源环境科技发展态势分析平台

The 2016 M7.8 Kaikoura (New Zealand) earthquake struck the east coast of the northern South Island, resulting in strong ground shaking and large surface fault slip. Since the earthquake was well recorded by a local strong-motion seismic network, near-fault data may provide direct measurements of dynamic parameters associated with the fault-weakening process. Here we estimate a proxy for slip-weakening distance D-c'', defined as double the fault-parallel displacement at the time of peak ground velocity, from accelerograms recorded at a near-fault station. Three-component ground displacements were recovered from the double numerical integration of accelerograms, and the corresponding final displacements are validated against coseismic displacement from geodetic data. The estimated D-c'' is 4.9 m at seismic station KEKS located similar to 2.7 km from a segment of the Kekerengu fault where large surface fault slip (similar to 12 m) has been observed. The inferred D-c'' is the largest value ever estimated from near-fault strong motion data, yet it appears to follow the scaling of D-c'' with final slip for several large strike-slip earthquakes. The energy budget of the M7.8 Kaikoura earthquake inferred from the scaling of D-c'' with final slip indicates that a large amount of energy was dissipated by on-and off-fault inelastic deformation during the propagation of the earthquake rupture, resulting in a slower average rupture speed (less than or similar to 2.0 km/s).

Plain Language Summary Slip-weakening distance is a parameter controlling the evolution of fault slip during an earthquake and is important for understanding rupture dynamics. However, it has been debated how large slip-weakening distance is and whether it scales with fault slip. We present evidence for large slip-weakening distance estimated from near-fault record of the recent magnitude 7.8 Kaikoura (New Zealand) earthquake. By examining seismic waveforms of the Kaikoura quake, we find that the slip-weakening distance is about 5 m on a portion of the Kekerengu fault, the largest value ever estimated directly from near-fault records. The large slip-weakening distance implies that a large amount of energy was dissipated by on-and off-fault inelastic deformation during the propagation of earthquake rupture, which may explain why the rupture propagation velocity of the Kaikoura quake was slower than that of most crustal earthquakes.