A review on slow earthquakes in the Japan Trench

Slow earthquakes are episodic slow fault slips. They form a fundamental component of interplate deformation processes, along with fast, regular earthquakes. Recent seismological and geodetic observations have revealed detailed slow earthquake activity along the Japan Trench—the subduction zone where the March 11, 2011, moment magnitude (Mw) 9.0 Tohoku-Oki earthquake occurred. In this paper, we review observational, experimental, and simulation studies on slow earthquakes along the Japan Trench and their research history. By compiling the observations of slow earthquakes (e.g., tectonic tremors, very-low-frequency earthquakes, and slow slip events) and related fault slip phenomena (e.g., small repeating earthquakes, earthquake swarms, and foreshocks of large interplate earthquakes), we present an integrated slow earthquake distribution along the Japan Trench. Slow and megathrust earthquakes are spatially complementary in distribution, and slow earthquakes sometimes trigger fast earthquakes in their vicinities. An approximately 200-km-long along-strike gap of seismic slow earthquakes (i.e., tectonic tremors and very-low-frequency earthquakes) corresponds with the huge interplate locked zone of the central Japan Trench. The Mw 9.0 Tohoku-Oki earthquake ruptured this locked zone, but the rupture terminated without propagating deep into the slow-earthquake-genic regions in the northern and southern Japan Trench. Slow earthquakes are involved in both the rupture initiation and termination processes of megathrust earthquakes in the Japan Trench. We then compared the integrated slow earthquake distribution with the crustal structure of the Japan Trench (e.g., interplate sedimentary units, subducting seamounts, petit-spot volcanoes, horst and graben structures, residual gravity, seismic velocity structure, and plate boundary reflection intensity) and described the geological environment of the slow-earthquake-genic regions (e.g., water sources, pressure–temperature conditions, and metamorphism). The integrated slow earthquake distribution enabled us to comprehensively discuss the role of slow earthquakes in the occurrence process of the Tohoku-Oki earthquake. The correspondences of the slow earthquake distribution with the crustal structure and geological environment provide insights into the slow-earthquake-genesis in the Japan Trench and imply that highly overpressured fluids are key to understanding the complex slow earthquake distribution. Furthermore, we propose that detailed monitoring of slow earthquake activity can improve the forecasts of interplate seismicity along the Japan Trench

Spatio-temporal chaos of one-dimensional thin elastic layer with the rate-and-state friction law

The rate-and-state friction (RSF) law is an empirical law often used to model the behavior of rock friction and reproduce the behavior of earthquakes. Recently, the model has been expanded to include so-called slow earthquakes, which are observed at the margins between steadily sliding aseismic and seismogenic zones. In this study, we incorporate the RSF law into a one-dimensional elastic layer spanned perpendicular to the loading direction as a model for the marginal area between aseismic and seismogenic zones. We obtained the complex Ginzburg-Landau equation near a Hopf bifurcation, and showed that the system has Benjamin-Fair instability, leading to spatio-temporal chaos. We conducted numerical calculations near the Hopf bifurcation point, and showed that an irregular oscillation appears when parameters with Benjamin-Feir instability are employed. The size of slip event showed an exponential distribution that resembles a type of slow earthquake.Comment: 33 pages, 7 figure

地震波観測の視点からみた地震の破壊表面エネルギー : 特集「地震発生の物理からみた地震発生帯堀削」

Fracture surface energy, Gc, is one of the fundamental parameters that governs earthquake rupture propagation and seismic energy radiation.Unlike other parameters of friction, it is relatively easily estimated using seismic observations.In this paper we consider two aspects of Gc, 1) the implications of the minimum Gc for the scaling of seismic energy, and 2) spatial distribution of Gc calculated from kinematic source models.Analyses of Gc based on seismic observations are important when comparing in-situ and laboratory observations of fault materials, which will be obtained in the Nankai-drilling project

Efficacy of Temporary Transvenous Pacing to Prevent Atropine-resistant Bradycardia during Surgery for a Tumor in the Brainstem Region : A Case Report

Article信州医学雑誌 64(3): 153-157(2016)journal articl

Metasurface-Enabled Multifunctional Single-Frequency Sensors without External Power

IoT sensors are crucial for visualizing multidimensional and multimodal information and enabling future IT applications/services such as cyber-physical space, digital twins, autonomous driving, smart cities, and virtual/augmented reality (VR or AR). However, IoT sensors need to be battery-free to realistically manage and maintain the growing number of available sensing devices. Here, we provide a novel sensor design approach that employs metasurfaces to enable multifunctional sensing without requiring an external power source. Importantly, unlike existing metasurface-based sensors, our metasurfaces can sense multiple physical parameters even at a fixed frequency by breaking classic harmonic oscillations in the time domain, making the proposed sensors viable for usage with limited frequency resources. Moreover, we provide a method for predicting physical parameters using the machine learning-based approach of random forest regression. The sensing performance was confirmed by estimating temperature and light intensity, and excellent determination coefficients larger than 0.96 were achieved. Our study affords new opportunities for sensing multiple physical properties without relying on an external power source or needing multiple frequencies, which markedly simplifies and facilitates the design of next-generation wireless communication systems.Comment: 47 pages, 23 figure

成人を対象としたメタ記憶測定尺度の開発 : MIA(The Questionnaire for Metamemory in Adulthood)日本語版作成の試み

Though it is inevitable to avoid deterioration of memory ability by aging, the quality of life varies in the way of recognizing the ability. It is called metamemory that how people recognize the ability of their memory. Metamemory is an important factor when investigating the quality of life in adulthoods, especially in elder persons. We developed a Japanese version of MIA (The questionnaire for Metamemory in Adulthood, Dixon, et al., 1983, 1988), and analyzed the data collected from 346 Japanese participants. They are consisted of two groups of students (N=302, m=20.4±1.91,18-37years,female=230, male= 72) and elders (N=44, m=69.4±4.75, 60-81years, female=34, male=10). As a result of factor analysis, the original seven factors (Achievement, Anxiety, Capacity, Change, Locus, Strategy and Task) were found to be replicable with the Japanese version of MIA. We discuss the differences from the original factor structure

Mobilization and Drainage of the Pancreatic Bed as a Treatment for Severe Acute Pancreatitis

A new surgical procedure, mobilization and drainage of the pancreatic bed, was performed on two cases of severe acute pancreatitis in shock state, one edematous type and another necrotic type, and prompt improvement of shock state and excellent healing of pancreatitis were observed clinically. The authors have experimentally proved that shock in acute pancreatitis developed as the retroperitoneal tissues directly absorbed the pancreatic exudate. The advantage of this surgical procedure was also proved on experimental dogs whose severe hypotension was successfully treated. The authors believe that this procedure is a simple and reasonable surgical method for acute pancreatitis