In this study, we estimated a three-dimensional structure of deep sedimentary layers around the Tachikawa fault using the receiver function analysis of earthquake records obtained in the K-NET, KiK-net and SK-net. The 63 stations in this area were used in the analysis. We calculated the receiver functions from 20 to 50 ground motion records obtained at each station, and deduced a 1-D subsurface structural model using an inversion based on the simulated annealing method. Then, we constructed a three-dimensional structures of the deep sedimentary layers in this area from integrating the 1-D S-wave velocity profiles at all the stations. The basement depth at hanging-wall side of the Tachikawa fault is larger than that at foot-wall side with a difference of about 1.7km in the 3-D model. Moreover, we calculated ellipticties for fundamental Rayleigh waves using this three dimensional model to compare observed horizontal-to-vertical ratio of earthquake data during the 2011 off the Pacific coast of Tohoku Earthquake. It is indicated that the characteristics of the calculated predominant periods of the ratios show good agreement with the observed ones.

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  I report about the following two corrections and their validation to better the performance of microtremor exploration method using mini-arrays (Centerless Circular Array method): one is an up-graded formulation of long wavelength approximation to convert CCA coefficient calculated from observed microtremor records to the estimate of phase velocity of Rayleigh waves; another a formulation using cross correlations of records of huddle test and field measurement to correct the difference of system response among the channels of data acquisition system. Both of them have shown an improvement of dispersion curve determination. Its effects, however, is limited and a drastic widening of analyzable frequency range toward lower one seems difficult when short period seismometers are used, because it is guessed that the electric noise floor of the recording system may control the lowest analyzable frequency.
  The experiment showed that in the ground similar as the reported site it may be possible to explore the ground shallower than the engineering bedrock in the frequency range higher than, for example, 3Hz, using CCA method with affordable moving coil type seismometers of short period for engineering purpose. More experiences of exploration are needed in grounds of various ground velocity structures.

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  The induced polarization (IP) method is used in many cases of exploration for nonferrous metal ore deposits such as porphyry copper and iron-oxide-hosted copper-gold deposits. This is because sulfide minerals such as pyrite and chalcopyrite have the IP effect. However, these sulfide minerals or target metal minerals are not often found in places where IP anomalies are observed. One of the reasons for this is the existence of magnetite, which also has the IP effect. One of the methods used to identify sulfide minerals and magnetite is the spectral IP (SIP) method, which measures complex resistivity at many frequencies. Although the SIP effect on sulfide minerals has been investigated, the SIP effect on magnetite has not been thoroughly examined. To investigate the difference in the SIP effect between sulfide minerals and magnetite, we measured the complex resistivity of artificial samples that contained pyrite particles and magnetite particles. Then, we tried to analyze the complex resistivity data using Cole-Cole models. The results show that the complex resistivities of the artificial samples have different frequency dependencies, even though the SIP effects of both become larger as the content of particles is increased. This indicates that the subsurface distribution of sulfide minerals and magnetite can be identified using the SIP method.

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  A Hot Dry Rock (HDR) geothermal energy development project has been conducted by Geodynamics Limited (GDY) at Cooper Basin in South Australia since 2002. The project site was selected where high temperature granite locates at relatively shallower depth estimated by the temperature distribution map and the seismic reflection and the gravity survey results. A water injection well, Habanero 1, was drilled to a depth of 4,421m where a temperature was measured around 250 degree C.
  The authors conducted the electromagnetic surveys around Habanero 1 to evaluate the underground resistivity structure through the collaboration with GDY. Joint inversion analysis of the CSAMT and TDEM methods showed that a relatively high resistivity zone of tens to 100 ohm-m locates at shallower than tens m and below this depth very low resistivity formations of a few ohm-m continue to a depth of about 5km. These low resistivity formations are considered to be caused by high salinity water in the formation pores. At the Jolokia site located 10 km west of Habanero 1, the similar resistivity structure was analyzed by the TDEM method. Therefore the almost same underground structure extends widely in Cooper Basin. These resistivity structures will be used as reference structures for evaluating water distribution when large volume of water will be injected into the granite to extract heat energy from the granite in the future.
  In 2003, hydraulic stimulation operations were performed to create artificial HDR reservoirs in Habanero 1 with injecting water at a maximum well-head pressure of 64 MPa and a total volume of 20,000 ton. During these operations, the authors observed AE (acoustic emission) events which are considered to be occurred with fractures progression. These fractures compose HDR reservoirs. More than 10,000 AE events were detected and 4,987 of them were located. Hypocenter locations of these events distributed southern area from Habanero 1 at first, and then the distribution spread north-east. According to the hypocenter distribution, Habanero 2, 3, and 4 were drilled as production wells to penetrate the created reservoirs. These three wells were hydraulically connected to Habanero 1 successfully. However, Habanero 2 and 3 were abandoned by stacking drilling tools and casing problems. Water circulation between Habanero 1 and Habanero 4 through the reservoir was successfully conducted and produced electricity of 1 MW in 2013.
  The geophysical exploration methods have contributed to develop geothermal energy in Australia.

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[in Japanese]

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