Crustal Structure, Imaged by 3D Seismic Attenuation, Exerts Influence on Multiple Fault Rupture of the Kaikoura M7.8 Earthquake, New Zealand

Session: Advances in Upper Crustal Geophysical Characterization [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The 2016 Mw 7.8 Kaikoura, New Zealand, earthquake occurred along the eastern margin of transition region between active subduction in the North Island and oblique collision in the South Island. To infer crustal properties, we imaged Q (1/seismic attenuation) by combining selected M>3.5 aftershocks with data from previous Q models. For 158 distributed aftershocks, we fit spectral decay on temporary stations and all Geonet stations, providing 6194 t*p and 19,497 t*s. The complex earthquake ruptured an ~180-km long zone of multiple faults, which involved jumping around the complicated eastern end of the Hope fault, without significant slip on the Hope fault. The Qs and Qp results show features in the upper and lower crust which relate to the distribution and types of fault rupture. This earthquake involved numerous faults over a region of greywacke crust, where the underlying high Q Cretaceous slab is about 30-km depth. It initiated with ~5m slip on the Humps fault where the fault bounds a region of low Q lower crust. The central region near Kaikoura shows a high Q strong crustal block, which appears to have inhibited rupture; as the rupture progressed over several small faults to jump offshore of the strong block. In the northern section, in a region of relatively uniform moderate to low Q, the earthquake evolved into the relatively continuous ~80-km long major rupture along the Jordan, Kekerengu and Needles faults, with ~20 m dextral slip at depth and surface displacements of ~10 m dextral and ~2 m vertical. The northern progression of the rupture stopped when it ran into a wall of high Q across Cook Strait. At 20-30-km depth northwest of the rupture, deeper zones of low Q are consistent with regions of distributed ductile shear and creep where the observed afterslip may have occurred.

Presenting Author: Donna Eberhart-Phillips

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