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Imaging of potential geothermal structures in Japan,

New Zealand, and Kenya inferred from ambient noise

and machine learning approaches

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Chanmaly Chhun (Kyushu Univ. & Univ. Tokyo)

Takeshi Tsuji (Kyushu Univ. & Univ. Tokyo)

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Conclusions

By applying ambient noise analysis and our machine learning models to seismometer and/or borehole data, we can obtain the key findings as follows: 

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In Paka - Silali volcanoes, Kenya:

  • S-wave velocity decreases beneath Silali and Paka volcanoes (magma chambers > 3km).
  • Most potential geothermal pathways are normal to the rift floor structure of volcanic axis.

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In Taupo volcanic zone, New Zealand:

  • Update geothermal fields and reveal new potential geothermal reservoirs (low Vs anomaly).
  • Shallow seismicity seems to be accumulated at low/high boundary velocity zones or related to geothermal fluid extraction.
  • 3D temperature models (and others) can be obtained from 3D Vs and log data via machine learning. Hot fluids are consistent with flow paths through the structure.

Conclusions

3D S-wave velocity model >> 3D Temperature model

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In Kuju volcanoes, Japan:

  • Revealed existing & new geothermal reservoirs in high resolution.
  • Potential geothermal structure is aligned to the NW-SE seismic anisotropy.
  • Dense seismicity is around the boundary of low- and high-velocity zones (i.e., fluid flows triggering seismicity).

Conclusions

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This study was supported by the Science and Technology Research Partnership for Sustainable Development (SATREPS) & The New Energy and Industrial Technology Development Organization (NEDO), Japan, and partially supported by the Japan Society for the Promotion of Science (KAKENHI grant JP20H01997, JP21H05202, and JP22H05108).

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We are greatly indebted to Yasuhiro Fujimitsu (Kyushu Univ.) for the SATREPS project supervision & support.

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We thank the IRIS Data Management Center (IRISDMC) http://www.fdsn.org/networks/detail/1C_2011/ for providing the open seismometer data from Kenya (Velasco et al., 2011) and from Bannister (2009) or http://fdsn.adc1.iris.edu/networks/detail/Z8_2009/.

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A deep appreciation goes to Koichiro Watanabe (JICA senior advisor) for introducing me geothermal geology and volcanology during field itinerary to the UNZEN-ASO-KUJU volcanoes on October 8-10, 2022.

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Seismicity is from JMA (https://www.data.jma.go.jp/svd/eqev/data/bulletin/hypo_e.html) and Andajani et al., (2023).

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Great thanks to Fernando Lawrence, Bokani Nthaba, and Tsuji labmates for technical helps.

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Acknowledgements

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