Journal of the Geothermal Research Society of Japan
Online ISSN : 1883-5775
Print ISSN : 0388-6735
ISSN-L : 0388-6735
Volume 40, Issue 3
Displaying 1-3 of 3 articles from this issue
Article
  • Yusuke YAMAYA, Shinichi TAKAKURA, Hiroshi ASANUMA
    2018 Volume 40 Issue 3 Pages 159-173
    Published: July 25, 2018
    Released on J-STAGE: January 25, 2019
    JOURNAL FREE ACCESS

    Since 2013, an engineered / enhanced geothermal system (EGS) experiment has been conducted at the Okuaizu geothermal field with the goal of recovering steam and stabilizing steam production. In this experiment, river water is injected near the geothermal reservoir to make up for a lack of natural recharge. We conducted repeated audio-frequency magnetotelluric (AMT) measurements to monitor the resistivity variation of the geothermal reservoir and nearby hot springs aquifer at the initial stage of the water injection. The initial AMT data before the water injection were collected along a line crossing the injection point in November 2013. The water injection was started in June 2015. A second set of AMT measurements at the same location was obtained at the end of August 2015. The total amount of water injected by that time was 1.2 × 105 t. The precise resistivity sections to a depth of about 1.5 km were analyzed from the two-dimensional inversion using the AMT data for both periods. The findings were consistent with the resistivity logging data of nearby wells. A comparison of the two sections indicates that the resistivity of the reservoir, including the caprock, increased between the two AMT measurements. The second section showed the resistive features of the reservoir and its caprock. The rise in resistivity suggests that the superheated steam progressed at depth and the effect of water injection had not yet appeared. AMT is an effective technique for monitoring geothermal reservoirs, although more precise measurements will be required to recognize the micro-resistivity variation associated with water injection.

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  • Hirofumi MURAOKA, Seiichiro IOKA, Yota SUZUKI
    2018 Volume 40 Issue 3 Pages 175-191
    Published: July 25, 2018
    Released on J-STAGE: January 25, 2019
    JOURNAL FREE ACCESS

    Unrecorded boiling-fountains with the discharge temperature 98.0 ºC and pH 7.5 were discovered in the eastern moat of Onikobe caldera, Japan in late November 2016, and are temporarily named “Eaigawa-jyoryu fountains” in this paper. Time-sequential observation of aerial photographs shows that the Eaigawa-jyoryu fountains appeared during the process of the aftershocks of the 2008 Iwate-Miyagi Inland Earthquake between 16 June 2008 and 21 May 2009. Based on the hypocenter distribution of the aftershocks of the 2008 IwateMiyagi Inland Earthquake, the main shock is ascribed to the rupture of a large-scale reverse fault where the western crustal block was thrusting over the eastern crustal block. The bottom of the hypocenter distribution of the aftershocks has, however, distinctive features. It is the deepest between Yakeishidake and Kurikomayama volcanoes as deep as 10 km below the sea level (b.s.l.) and comes to be shallower to the north and south. It comes to be extremely shallower to the south up to the 4-3 km depth b.s.l. near Onikobe caldera. It gradually comes to be shallower from the center to the east like the typical reverse fault rupture but abruptly reaches to be shallower to the west up to the 4-3 km depth b.s.l. near Kurikomayama volcano, Takamatsudake volcano and Onikobe caldera. The earthquake hypocenters were thus compulsorily confined to be shallower by the brittleplastic transition surrounding the sub-volcanic magma systems beneath these volcanoes throughout the events of the main shock and aftershocks. The right-lateral shear strain concentration made the pore pressure increased in an ENE-WSW trending narrow zone between the southern edge of the large-scale reverse fault of the main shock and the northern edge of the plastic ridge at the Katayama-Arayu steaming grounds in Onikobe caldera during the main shock of the 2008 Iwate-Miyagi Inland Earthquake. This right-lateral shear strain concentration might have ruptured a small-scale ENE-WSW trending right-lateral strike-slip fault in the process of the aftershocks presumably initiating the new discharge of the Eaigawa-jyoryu fountains.

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Technical Report
  • Masahiko KATSURAGI, Hikari FUJII, Satoru KURONUMA, Jun INOUE, Mutsumi ...
    2018 Volume 40 Issue 3 Pages 193-206
    Published: July 25, 2018
    Released on J-STAGE: January 25, 2019
    JOURNAL FREE ACCESS

    Air-conditioning systems with groundwater heat pumps using the Aquifer Thermal Energy Storage (ATES) are known to be highly effective for reducing carbon dioxide emission and saving energy.

    In order to build the ATES systems, pumping and recharge wells must be drilled, but national and regional governments have strict regulations for pumping groundwater especially in the urban areas for preventing the land subsidence due to the excessive pumping of groundwater during the high economic growth period in the Japanese society.

    In this research, the social systems such as legal regulations to use groundwater were focused to investigate the applicability of ATES systems in populated areas of Japan. 

    As a result of investigation, more than half of all households are limited by social systems when ATES is introduced. The restricted areas are mainly concentrated around the three major urban areas of Japan. In order to promote the introduction of ATES, the suitability of these social systems should be first investigated.

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