Abstract
Seismic events produced by block rotations about vertical axis occur in many geodynamic contexts. In this study, we show that these rotations can be accounted for using the proper theory, namely micropolar theory, and a new asymmetric moment tensor can be derived. We then apply this new theory to the Kaikōura earthquake (2016/11/14), Mw 7.8, one of the most complex earthquakes ever recorded with modern instrumental techniques. Using advanced numerical techniques, we compute synthetic seismograms including a full asymmetric moment tensor and we show that it induces measurable differences in the waveforms proving that seismic data can record the effects of the block rotations observed in the field. Therefore, the theory developed in this work provides a full framework for future dynamic source inversions of asymmetric moment tensors.
Highlights
The main deformation observed on continents is generated by the contemporaneous motion of numerous strike-slip faults (Schreurs, 1994)
The study of general features of the deformation induced by systems of sub-parallel strike-slip faults shows that the governing constraints are kinematic: the fault blocks must remain in contact with each other and the deformed area must fit with its surroundings
Fault blocks that move laterally without significant internal deformation rotate about vertical axis relative to boundaries of the fault domain by an amount that is quantitatively related to the fault slip, spacing and orientation (Freund, 1970; Garfunkel, 1974; Garfunkel & Ron, 1985)
Summary
The main deformation observed on continents is generated by the contemporaneous motion of numerous strike-slip faults (Schreurs, 1994). The deformation produced by the rotation of kilometer-scale blocks in zones of distributed brittle deformation in the crust has been modeled combining different types of fault blocks models with the seismic moment tensor Twiss et al (1993) establishes this connection using micropolar theory (Nagahama & Teisseyre, 2000; Teisseyre, 1973, 2008, 2011; Teisseyre et al, 2006, 2008) This allows to model the discontinuous nature of faulting of distributed brittle deformation as a continuum, provided that the dimensions of the deforming material are large relative to the characteristic spacing of the discontinuities. We discuss the contributions and further perspectives of this work
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