今週のうなぎセミナーについてお知らせいたします。

Here is information of the Unagi-seminar(December, 19).

************** Seminar on Seismology IV B, D /地震学ゼミナールIV B, D (Unagi Seminar) **************

科目：地震学ゼミナールIV B, D / Seminar on Seismology IV B, D（修士・博士）
日時：2024年 12月 19日 (木) 13:30~
場所：京都大学 防災研究所 本館E-232D

Date and Time：2024-12-19, 13:30~
Place：Uji Campus Main Building E232D

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Speaker 1（発表者）:　Reiju Norisugi

Title（題目）:
Rate- and Roughness-Dependent Fault Constitutive Law and Dynamic Earthquake Sequence Simulation

Abstract（要旨）:
What physics governs the multi-scale source property of earthquakes, such as fracture energy scaling (e.g., Viesca & Garagash, 2015), is still in debate, an interesting question. We introduce the rate- and roughness-dependent fault constitutive law (RRF), accounting for the multiscale roughness evolution, and show that RRF can readily reproduce the fracture energy scaling on the uniform fault. To obtain the RRF framework, we regularized the previously proposed slip- and time-dependent fault constitutive law (Matsu’ura et al., 1992; Aochi & Matsu’ura, 2002) into the form of the rate-and-state friction (RSF) (Dieterich 1978, 1979; Ruina, 1983) by adding the direct effect term. The RRF is a type of expansion from single to multiple state variable formulation of the RSF. It involves multi-scale weakening distances for asymptotic evolution of shear strength as a response to displacement due to the state variable evolution.
We perform the dynamic earthquake sequence simulation (Lapusta et al., 2000; Noda 2022) with RRF. The previous adaptive time step evolution scheme is only valid for the single-state variable formulation. Thus, we utilized a more flexible (but time-consuming) scheme by Romanet & Ozawa (2022). For computational efficiency (and avoiding complex copy-right problems) we implement the simulation by PyTorch, a Python library for Deep Learning, and make it possible to compute earthquake sequence simulation on a single GPU and multiple CPUs. We will discuss RRF's properties in the continuum model and its implications for natural earthquakes.

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Speaker 2（発表者）:　野末 陽平 (Yohei Nozue)

Title（題目）:
Influence of the 2011 Tohoku-oki earthquake on the strain-rate field around the Noto Peninsula

Abstract（要旨）:
Before the M7.6 Noto Peninsula earthquake on 1 January 2024, which caused severe damage, an earthquake swarm started from May 2018 and became very active after December 2020 in the northeastern tip of the Noto Peninsula (e.g., Amezawa et al. 2023; Yoshida et al. 2023). It is widely considered that the swarm activity was triggered by upward migration of fluids with a large volume, as exemplified by GNSS data that showed horizontal inflation and uplift around above the swarm area (Nishimura et al. 2023). However, the cause of the upward fluid migration has hardly been discussed. In this study, we consider this problem focusing on geodetic data. By applying a geodetic data inversion method based on basis function expansion, which is introduced in Okazaki et al. (2021), to GNSS data in central Japan, we estimate the temporal change of strain-rate fields before and after the 2011 Tohoku-oki earthquake. Because of the postseismic deformation of the 2011 Tohoku-oki earthquake, the estimated strain-rate fields show a drastic change before and after the 2011 Tohoku-oki earthquake: dilatation rates and EW contraction rates reversed from contraction to extension in a wide area including the Noto Peninsula. The obtained strain-rate fields are further converted to the stress-rate fields under the condition of an isotropic elastic medium. Then, we find the cumulative extensive stress reached 15-30 kPa in the northeastern tip of the Noto Peninsula after the 2011 Tohoku-oki earthquake. The extensive stress field should facilitate upward fluid migration, which would trigger the swarm activity in the Noto Peninsula since 2018.
I submitted the paper to the special issue on "The 2024 M7.6 Noto Peninsula Earthquake and Seismic Swarm" in October. After the manuscript had been assessed by the reviewers, I received the editorial decision that it needed major revision this month. In this seminar, I will talk about the research above according to the manuscript, and then introduce the answers to some of the reviewers' comments which I am thinking about now.

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