Determining the Maximum Depth of Hydrothermal Circulation Using Geothermal Mapping and Seismicity to Delineate the Depth to Brittle-Plastic Transition in Northern Honshu, Japan

Yota Suzuki,Seiichiro Ioka,Hirofumi Muraoka

doi:10.3390/en7053503

Yota Suzuki, Seiichiro Ioka + Show 1 more

Open Access

https://doi.org/10.3390/en7053503

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Journal: Energies	Publication Date: May 23, 2014
Citations: 25	License type: CC BY 4.0

Affiliation: Hirosaki University, Japan Research Institute

Abstract

This paper defines the maximum possible vertical extent of hydrothermal circulation in granitic crust, and thus the maximum depth within which geothermal reservoirs can be encountered. To evaluate prospective geothermal fields we constructed a geothermal database in northern Honshu, Japan that includes 571 points of thermal data of existing wells and hot springs. Depth-temperature curves were normalized by the Activity Index for three-dimensional extrapolation and a depth contour map of the 380 °C isotherm was plotted as an assumed brittle-plastic transition for granitic crust. Shallower-depth anomalies of the brittle-plastic transition on this map are closely coincident with the Quaternary volcanoes and their prospective geothermal fields. It should be noted that the bottom of the spatial distribution of seismicity in the volcanic fields shows strong correlation to the 380 °C isotherm. This result indicates reliability of the subsurface three-dimensional thermal map and suggests that the 380 °C isotherm strongly constrains the bottom surface of seismicity, fracturing and hydrothermal convection in granitic crust.

Highlights

Since the unprecedented disastrous Great East Japan Earthquake at 11 March 2011, geothermal energy is being re-evaluated as a more crucial energy resource, as green energy, and as indigenous energy in northern Japan
This paper describes a geothermal database in Aomori Prefecture and draws a map of the depth of the brittle-plastic transition based on some depth-temperature normalization techniques that allow three-dimensional extrapolation in up-flow zones
Based on the geothermal database for available thermal data such as wells and hot springs in Aomori Prefecture, northern Honshu, Japan, depth-temperature curves were normalized by the Activity Index for three-dimensional extrapolation and a depth contour map of the 380 °C isotherm was plotted as an assumed brittle-plastic transition for granitic crust

Summary

Introduction

Since the unprecedented disastrous Great East Japan Earthquake at 11 March 2011, geothermal energy is being re-evaluated as a more crucial energy resource, as green energy, and as indigenous energy in northern Japan. 27,219 hot spring sources are distributed all over Japan [1], and numerous hot springs are concentrated in Aomori Prefecture, a northern end of Honshu Island, Japan (Figure 1) Most of these Japanese hot springs are artificially developed by shallow wells. This paper describes a geothermal database in Aomori Prefecture and draws a map of the depth of the brittle-plastic transition based on some depth-temperature normalization techniques that allow three-dimensional extrapolation in up-flow zones. This map of the depth of the brittle-plastic transition is verified by the bottom of seismicity which is far independent destruction phenomena from the thermal structure concerned. We used the Generic Mapping Tools 4.5.9 for drawing most of figures in this paper [2]

Geothermal Database

Estimate of Subsurface Geothermal Structure

Discussion

Conclusions