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| | Abstract | | In November 2018, we conducted the seismic study at the Medipolis geothermal field. We deployed ground surface geophones and a fiber-optic cable for the DAS in the well. Ground surface geophones exhibited unusual waveform characteristics such as the amplitudes of the first arriving P-waves in some earthquakes on UD geophones are small, but the EW and NS geophones exhibited weak P first arrivals and successive intense phase with a delay of 0.8 s. When we assume the Vp/Vs = 3 zone at a depth of 4 km, the models can explain the observed characteristics. We conclude that this phase is the P-to-S converted phase. Considering that the Poisson's ratio of water is 0.5, the high Vp/Vs zone could be at the supercritical state of water. |
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