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Décollement geometry controls on shallow very low frequency earthquakes
Yoshitaka Hashimoto1, Shigeyuki Sato2, Gaku Kimura3
1Department of Global Environment and Disaster Prevention, Faculty of Science and Technology, Kochi University, Akebonocho 2-5-1, Kochi, 780-8520, Japan. hassy@kochi-u.ac.jp.
Shallow very low frequency earthquakes (VLFE) in subduction zones are influenced by plate interface stress. Décollement geometry, not material properties, primarily controls VLFE activity and migration towards the trench.
Area of Science:
- Geophysics
- Seismology
- Tectonics
Background:
- Shallow very low frequency earthquakes (VLFE) are increasingly documented in subduction zones.
- Plate interface characteristics, including material heterogeneity and stress, dictate variable slip rates.
- Décollement geometry and regional stress significantly influence stress distribution and material properties.
Purpose of the Study:
- To determine the stress distribution along the shallow décollement in the Nankai Trough.
- To map normalized slip tendency (Ts') and dilation tendency (Td) in the study area.
- To investigate the relationship between stress distribution and VLFE occurrence.
Main Methods:
- Utilized three-dimensional (3D) seismic surveys.
- Conducted regional stress analysis.
- Generated maps of normalized slip tendency (Ts') and dilation tendency (Td).
Main Results:
- VLFE alignments correlate with trends in Ts' and Td.
- Areas with low Ts' and Td appear to act as barriers to VLFE migration towards the trench.
- The distribution of stress was mapped along the shallow décollement.
Conclusions:
- Décollement geometry is the primary control on shallow VLFE activity.
- Regional stress and décollement geometry, independent of sediment properties, explain observed VLFE patterns.
- Stress distribution, as indicated by Ts' and Td, governs VLFE migration and occurrence patterns.
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