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Observation of seafloor strain caused by shallow SSE and VLFE fault in the Nankai Trough by seafloor fiber optic strainmeters

Authors

Araki,  Eiichiro
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Yokobiki,  Takashi
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Baba,  Satoru
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Yamamoto,  Yojiro
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Zumberge,  Mark
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Nishida,  Shuhei
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Machida,  Yuya
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Matsumoto,  Hiroyuki
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Citation

Araki, E., Yokobiki, T., Baba, S., Yamamoto, Y., Zumberge, M., Nishida, S., Machida, Y., Matsumoto, H. (2023): Observation of seafloor strain caused by shallow SSE and VLFE fault in the Nankai Trough by seafloor fiber optic strainmeters, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-2395


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5018362
Abstract
Slow slip occurs repeatedly in the shallow part of the plate subduction boundary region in the Nankai Trough (Araki et al., 2017). To investigate its activity in wider area, we developed and installed a seafloor fiber-optic strainmeter connected to a submarine cable observation network (DONET) in west of the previous observation network in the borehole in 2019. In January-February, 2022, the seafloor fiber-optic strainmeter observed slow transient extension of about 0.7 μstrain over 3 weeks. Very low-frequency earthquakes (VLFEs) were observed in the vicinity during this period. The fiber-optic strainmeter was able to observe slow step-like changes for many of the VLFEs that occurred near the strainmeter. We observed strain change about 20 n strain for a VLFE of Mw 4.4. The observed strain change polarity and transitions were consistent with those expected from the focal mechanisms of the VLFEs, suggesting the possibility to investigate slip processes of each individual VLFE by seafloor fiber strain record. The strain changes by the local VLFEs were insufficient to account for the total slow 3-week strain change observed by the fiber optic strainmeter. Therefore, we propose that shallow slow slip occurred in the areas where the VLFEs were observed, and that the slow slip may have loaded individual VLFE faults into a burst-like cluster of VLFEs. We further expanded our strainmeter observations by adding two strainmeters in array and in different direction in November 2022, where we anticipate more robust and detailed fault slip analysis will be performed in the next similar slip occurrence.