[S-CG39] Science of slow earthquakes: Toward unified understandings of whole earthquake process

[SCG39-02] Depth-dependent deep-slow earthquakes controlled by temperature dependence of brittle-ductile transitional rheology

*Ryosuke Ando¹, Kohtaro Ujiie², Naoki Nishiyama², Yasushi Mori³ (1.Graduate School of Science, University of Tokyo, 2.Graduate School of Life and Environmental Sciences, University of Tsukuba, 3.Kitakyushu Museum of Natural History and Human History)

Keywords:Rheology, Fault rocks, Mathematical model, SSEs, LFEs, Heterogeneity

Recent geophysical observations have classified the deep-slow earthquakes, down-dip the seismogenic zone, into Long-term Slow Slip Events (L-SSEs), Short-term Slow Slip Events (S-SSEs), and Low-frequency earthquakes (LFEs) and tremor in the order from slow to fast. The same ordering has also become recognized as converted from the shallow to the deep in the source depths, apparently contradicting the well-established transitional behavior from the shallower brittle/fast regime to the deeper ductile/slow regime, as described by the “seismogenic inversion layer”. Here we propose a new mechanical model that can consistently explain these two, only by considering the competitive temperature-dependent effects on the fraction of the brittle material, Rb, and the viscosity of the ductile material, η, in fault zones. Our model is geologically motivated and is an extension of the previous physical model with the brittle-ductile heterogeneity on faults. The key to understanding the enigmatic depth dependencies is that the reduction of η is more significant than the reduction of Rb as increasing temperature. Our results highlight the importance of rock plasticity, rather than friction, and rheological heterogeneity as universal mechanisms of deep-slow earthquakes independent of tectonic environments.