FDM simulation of earthquakes off western Kyushu, Japan, using a land–ocean unified 3D structure model
Abstract Seismic activity occurred off western Kyushu, Japan, at the northern end of the Okinawa Trough on May 6, 2016 (14:11 JST), 22 days after the onset of the 2016 Kumamoto earthquake sequence. The area is adjacent to the Beppu–Shimabara graben where the 2016 Kumamoto earthquake sequence occurre...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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SpringerOpen
2017-07-01
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| Series: | Earth, Planets and Space |
| Subjects: | |
| Online Access: | http://link.springer.com/article/10.1186/s40623-017-0672-9 |
| _version_ | 1811266712827330560 |
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| author | Taro Okamoto Hiroshi Takenaka Takeshi Nakamura Tatsuhiko Hara |
| author_facet | Taro Okamoto Hiroshi Takenaka Takeshi Nakamura Tatsuhiko Hara |
| author_sort | Taro Okamoto |
| collection | DOAJ |
| description | Abstract Seismic activity occurred off western Kyushu, Japan, at the northern end of the Okinawa Trough on May 6, 2016 (14:11 JST), 22 days after the onset of the 2016 Kumamoto earthquake sequence. The area is adjacent to the Beppu–Shimabara graben where the 2016 Kumamoto earthquake sequence occurred. In the area off western Kyushu, a M7.1 earthquake also occurred on November 14, 2015 (5:51 JST), and a tsunami with a height of 0.3 m was observed. In order to better understand these seismic activity and tsunamis, it is necessary to study the sources of, and strong motions due to, earthquakes in the area off western Kyushu. For such studies, validation of synthetic waveforms is important because of the presence of the oceanic water layer and thick sediments in the source area. We show the validation results for synthetic waveforms through nonlinear inversion analyses of small earthquakes (~M5). We use a land–ocean unified 3D structure model, 3D HOT finite-difference method (“HOT” stands for Heterogeneity, Ocean layer and Topography) and a multi-graphic processing unit (GPU) acceleration to simulate the wave propagations. We estimate the first-motion augmented moment tensor (FAMT) solution based on both the long-period surface waves and short-period body waves. The FAMT solutions systematically shift landward by about 13 km, on average, from the epicenters determined by the Japan Meteorological Agency. The synthetics provide good reproductions of the observed full waveforms with periods of 10 s or longer. On the other hand, for waveforms with shorter periods (down to 4 s), the later surface waves are not reproduced well, while the first parts of the waveforms (comprising P- and S-waves) are reproduced to some extent. These results indicate that the current 3D structure model around Kyushu is effective for generating full waveforms, including surface waves with periods of about 10 s or longer. Based on these findings, we analyze the 2015 M7.1 event using the cross-correlations between the observed and synthetic waveforms. The result suggests a rupture propagation toward the NNE, with a major radiation about 25 km north of the onset point. Graphical Abstract . |
| first_indexed | 2024-04-12T20:48:16Z |
| format | Article |
| id | doaj.art-8cd24766475143e38dc3a109a9b3c297 |
| institution | Directory Open Access Journal |
| issn | 1880-5981 |
| language | English |
| last_indexed | 2024-04-12T20:48:16Z |
| publishDate | 2017-07-01 |
| publisher | SpringerOpen |
| record_format | Article |
| series | Earth, Planets and Space |
| spelling | doaj.art-8cd24766475143e38dc3a109a9b3c2972022-12-22T03:17:12ZengSpringerOpenEarth, Planets and Space1880-59812017-07-0169111510.1186/s40623-017-0672-9FDM simulation of earthquakes off western Kyushu, Japan, using a land–ocean unified 3D structure modelTaro Okamoto0Hiroshi Takenaka1Takeshi Nakamura2Tatsuhiko Hara3Department of Earth and Planetary Sciences, Tokyo Institute of TechnologyDepartment of Earth Sciences, Okayama UniversityEarthquake and Tsunami Research Division, National Research Institute for Earth Science and Disaster ResilienceInternational Institute of Seismology and Earthquake Engineering, Building Research InstituteAbstract Seismic activity occurred off western Kyushu, Japan, at the northern end of the Okinawa Trough on May 6, 2016 (14:11 JST), 22 days after the onset of the 2016 Kumamoto earthquake sequence. The area is adjacent to the Beppu–Shimabara graben where the 2016 Kumamoto earthquake sequence occurred. In the area off western Kyushu, a M7.1 earthquake also occurred on November 14, 2015 (5:51 JST), and a tsunami with a height of 0.3 m was observed. In order to better understand these seismic activity and tsunamis, it is necessary to study the sources of, and strong motions due to, earthquakes in the area off western Kyushu. For such studies, validation of synthetic waveforms is important because of the presence of the oceanic water layer and thick sediments in the source area. We show the validation results for synthetic waveforms through nonlinear inversion analyses of small earthquakes (~M5). We use a land–ocean unified 3D structure model, 3D HOT finite-difference method (“HOT” stands for Heterogeneity, Ocean layer and Topography) and a multi-graphic processing unit (GPU) acceleration to simulate the wave propagations. We estimate the first-motion augmented moment tensor (FAMT) solution based on both the long-period surface waves and short-period body waves. The FAMT solutions systematically shift landward by about 13 km, on average, from the epicenters determined by the Japan Meteorological Agency. The synthetics provide good reproductions of the observed full waveforms with periods of 10 s or longer. On the other hand, for waveforms with shorter periods (down to 4 s), the later surface waves are not reproduced well, while the first parts of the waveforms (comprising P- and S-waves) are reproduced to some extent. These results indicate that the current 3D structure model around Kyushu is effective for generating full waveforms, including surface waves with periods of about 10 s or longer. Based on these findings, we analyze the 2015 M7.1 event using the cross-correlations between the observed and synthetic waveforms. The result suggests a rupture propagation toward the NNE, with a major radiation about 25 km north of the onset point. Graphical Abstract .http://link.springer.com/article/10.1186/s40623-017-0672-9Okinawa TroughSeismic activity off western KyushuWaveform inversionFirst-motion augmented moment tensorFluid–solid interfaceHOT-FDM |
| spellingShingle | Taro Okamoto Hiroshi Takenaka Takeshi Nakamura Tatsuhiko Hara FDM simulation of earthquakes off western Kyushu, Japan, using a land–ocean unified 3D structure model Earth, Planets and Space Okinawa Trough Seismic activity off western Kyushu Waveform inversion First-motion augmented moment tensor Fluid–solid interface HOT-FDM |
| title | FDM simulation of earthquakes off western Kyushu, Japan, using a land–ocean unified 3D structure model |
| title_full | FDM simulation of earthquakes off western Kyushu, Japan, using a land–ocean unified 3D structure model |
| title_fullStr | FDM simulation of earthquakes off western Kyushu, Japan, using a land–ocean unified 3D structure model |
| title_full_unstemmed | FDM simulation of earthquakes off western Kyushu, Japan, using a land–ocean unified 3D structure model |
| title_short | FDM simulation of earthquakes off western Kyushu, Japan, using a land–ocean unified 3D structure model |
| title_sort | fdm simulation of earthquakes off western kyushu japan using a land ocean unified 3d structure model |
| topic | Okinawa Trough Seismic activity off western Kyushu Waveform inversion First-motion augmented moment tensor Fluid–solid interface HOT-FDM |
| url | http://link.springer.com/article/10.1186/s40623-017-0672-9 |
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