New and classical applications of heat flow studies

Abstract

This special issue of Journal of Geophysics and Engineering is dedicated to a collection of papers which resulted from an international workshop held in Aachen, Germany, on 4-7 October 2004, called 'New and Classical Applications of Heat Flow Studies'. This was the third in a series of topical geothermal workshops arranged by the Geothermal Working Group of the German Geophysical Society (DGG) and was organized by the Institute of Applied Geophysics at RWTH Aachen University under the auspices of the International Heat Flow Commission of the International Association of Seismology and Physics (IASPEI). The meeting was attended by some 60 scientists from 14 countries and three continents. Financial assistance, granted by DGG and IASPEI, allowed us to provide partial support for a total of eight students, young scientists and eminent researchers from eastern Europe and overseas. The convenors of the meeting were Christoph Clauser (Aachen), Thomas Kohl (Zurich) and Makoto Taniguchi (Kyoto). The main local organizers were Volker Rath (scientific programme) and Ute Kreutz (accommodation and financial affairs). The topics addressed in more than 50 oral and poster presentations indicated that today intriguing new applications of heat flow studies have emerged, complementing the classical topics of heat flow mapping and the tectonic implications of heat flow. In classical applications, for instance, thermal signatures of water flow or downward diffusion of variations in the Earth's mean temperature are considered as noise which needs to be corrected prior to further use of the data. In contrast, in several new applications it is exactly the information contained in these signatures which has been extracted and interpreted. For instance, over the past two decades, work on the most prominent of these new applications has been devoted to inverting the variation of the Earth's past mean ground surface temperature (GST). As of today, GST provided by the geothermal method has become widely recognized as a valuable supplement to established climate proxies. In contrast to these, GST is directly linked to climate-related temperature variations. It is based in a straightforward manner on heat transport and thermal physics and, in contrast to climate proxies, does not require transfer functions for relating temperature-sensitive phenomena to temperature.The second new application makes use of the signature of heat advection to identify and quantify flow in the deep subsurface. Based on high-quality data of sufficient number and distribution, the method's detection limit is far below that of any other technique. These are but two examples where, under a new perspective, noise has turned into signal. Last but not least, the potential of geothermal energy to supply low-pollution, low-carbon-dioxide electric power and heat has been recognized and exploited for more than 100 years, primarily in tectonically active regions with natural steam reservoirs. However, the ever-increasing price of fossil fuels and their exhaust of greenhouse gases have turned geothermal energy into an attractive option, even in geothermally less favourable regions. In this more demanding situation, understanding different heat transport processes requires more refined techniques for data correction, parameter identification and numerical simulation. This special issue comprises a selection of 11 papers which emerged from this meeting. Corresponding to the scope of the meeting, four papers address paleoclimatic topics, four papers deal with topics related to subsurface flow, and five papers discuss various aspects related directly or indirectly to geothermal energy. Thus, this special issue reflects exciting trends in current geothermal research. It illustrates that today geothermal research comprises new and challenging fields, with applications in environmental sciences, reservoir engineering, and climate and energy research.