Inversion for the Higher-Degree Moment Tensors of the 2016 Mw 7.8 Kaiköura Earthquake

Alan Juarez, & Thomas H. Jordan

Published August 7, 2019, SCEC Contribution #9364, 2019 SCEC Annual Meeting Poster #178

The Mw7.8 Kaikoura, New Zealand, earthquake of 2016 is one of the most complex earthquakes ever recorded. It ruptured more than twenty crustal faults with different strikes, dips, and rakes, as well as the subduction megathrust beneath New Zealand. Following Jordan & Juarez (GJI, 2019), any seismic source of arbitrary complexity can be represented as the sum of up to six orthogonal moment-tensor fields. In the point-source limit, the zeroth-degree (monopole) term is the centroid moment tensor (CMT), and each higher-degree term can be expressed as the product of a source-mechanism tensor orthogonal to the CMT (and to each other) and a multipole tensor. We have developed a sequential Bayesian method for estimating the higher-degree mechanisms and multipole tensors from seismic data and have applied the method to the Kaikoura earthquake. The first step inverts for the CMT; the second for the dipole term plus a CMT correction; the third for the quadrupole term plus lower-degree corrections; and so on. At each step, we check for the statistical significance of the highest-degree term. For the Kaikoura earthquake, we obtain dipole and quadrupole terms that are consistent with published finite-fault models. The higher-degree terms quantify the mechanism complexity of the source and the seismic radiation not represented by the CMT, and they provide integral constraints on space-time parametrizations of complex sources, such as finite fault inversions.

Key Words
Moment Tensor Fields, Inversion of Seismic Data

Citation
Juarez, A., & Jordan, T. H. (2019, 08). Inversion for the Higher-Degree Moment Tensors of the 2016 Mw 7.8 Kaiköura Earthquake . Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)