Study of accuracy of synthetic waveforms and earthquake occurrence site in and around the source area of the 2011 Tohoku-oki earthquake by using a land-ocean unified 3D structure model

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K05535
• 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: Tokyo Institute of Technology
• Principal Investigator: Okamoto Taro 東京工業大学, 理学院, 助教 (40270920)
• Co-Investigator(Kenkyū-buntansha): 竹中 博士 岡山大学, 自然科学研究科, 教授 (30253397)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 差分法 / GPU / 東北地方太平洋沖地震

Outline of Final Research Achievements

We evaluate the accuracy of synthetic waveforms for small earthquakes in the source area of the 2011 Tohoku-Oki earthquake (MJMA 9.0) at the Japan Trench. We compute the synthetic waveforms on the basis of a land-ocean unified 3D structure model using our HOT-FDM. In estimating the source parameters, we apply FAMT method that we have recently proposed. We find that the FAMT solutions for events with shallow-angle thrusting mechanisms are located near the plate interface, which demonstrates the importance of using a 3D model. We find that the full waveforms with periods shorter than about 10 s are not well reproduced. At periods around 4 s, the initial body waveforms can be modeled, but the later surface waves are difficult to reproduce correctly. We further examine the 3D sensitivity kernels: for short-period wavefield (below around 10 s) we observe a curved pattern which cannot be predicted by 1D earth models. This indicates the effects of 3D heterogeneity.

Free Research Field

固体地球科学

Academic Significance and Societal Importance of the Research Achievements

地震が発生した場所やメカニズムを推定するには地震波波形データが重要なデータとなる。一方で日本周辺の沈み込み帯は内部構造が複雑であるため地震波伝播にも大きな影響がある。これは地震解析の精度にも影響を及ぼすため、本研究では計算した地震波波形の精度を詳しく検討した。さらに地震波が構造モデルのどの部分に強く影響されているかを検討し、3次元構造モデルの効果などの構造モデルを改良する上での知見を得た。