Detection of missing triggered slow events toward understanding physical characteristics of the plate interface

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K05537
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Solid earth and planetary physics
• Research Institution: Kyoto University
• Principal Investigator: Miyazawa Masatoshi 京都大学, 防災研究所, 准教授 (80402931)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 超低周波地震 / 動的誘発 / ベイズ推定 / 粒子フィルタ / 2016年紀伊半島沖（三重県沖）の地震

Outline of Final Research Achievements

Remote triggering of very low-frequency (VLF) earthquakes in the Nankai subduction zone by surface waves from a moderate to large, distant earthquake was examined using a new approach. The triggering of another type of tectonic slow earthquake/tremor and slow slip was previously discovered using simple signal processing techniques. A Bayesian technique was developed to detect seismic signals and estimate the maximum likelihood source parameters of VLF earthquakes that might have been remotely triggered. This approach was applied to seismograms of the 2016 Mw 5.9 off-Kii Peninsula earthquake, recorded in western Shikoku. Six VLF earthquakes with magnitudes from 3.4 to 4.3 likely occurred in the seismogenic regions of ambient low-frequency earthquakes/tremors (LFEs), and were likely triggered by the arrivals of high-amplitude surface waves. These VLF earthquakes were more sensitive to stress changes than LEEs. This is the first reported example of dynamic triggering of VLF earthquakes.

Free Research Field

地震学

Academic Significance and Societal Importance of the Research Achievements

沈み込み帯で発生するスローイベントのうち、超低周波地震だけが動的誘発されていることが見つかっていなかった。本研究により、超低周波地震も他のスローイベントと同様に動的に直接誘発される事が確認され、プレートの沈み込み帯におけるプレート境界の特徴についての理解が進み、巨大地震発生に掛かるメカニズムの解明に貢献すると考えられる。