Vol.9 No.2 2016

Research paper : Development of rock deformation techniques under high-pressure and high-temperature conditions (Koji MASUDA)−101−Synthesiology - English edition Vol.9 No.2 (2016) and Heard of the Shell Technology Center in Houston, USA, subsequently developed the technology further.[10] At present, rock experiments continue to be conducted in oil company laboratories, or with funding from oil companies, in relation to the development of shale gas. At the Geological Survey of Japan in the 1960s, Hoshino et al. designed several original devices for experimental deformation of rocks based on an apparatus used in the United States and produced prolific experimental data.[11] An experimental apparatus that used gas pressure was developed in the 1960s by Paterson at the Australian National University; this device was sold throughout the world through a spin-off company and was used widely in both Europe and the United States.[12] In the late 1990s, I considered purchasing this apparatus and went to Australia, where Paterson showed me the factory where the apparatus was made. However, because it was very troublesome at that time to arrange for an inspection and obtain clearance for the import of an apparatus using high-pressure gas, I did not purchase the apparatus. Instead, we, the AIST research team, developed a custom experimental system by integrating our own original technology with existing technology.Recently, samples of actual fault rocks have been retrieved from deep underground by deep drilling projects that penetrated a fault zone. By measuring the physical properties of such samples in the laboratory, understanding of the large-scale slip that occurred in the shallow part of the fault zone during the 2011 off the Pacific coast of Tohoku Earthquake has been enhanced.[13] Currently, the most important challenge in the field of rock experimentation is to find and generalize the physical laws that govern various fault behaviors, to extract the parameters of a constitutive equation, and to fuse these findings with research on earthquake simulation by numerical models. To construct such a model, an accurate understanding of earthquake occurrence processes is mandatory. This paper reports on technologies and methods that have been developed in the effort to meet this challenge.3 Issues in reproducing earthquake processesAn earthquake occurs when a fault beneath the Earth's surface moves. Therefore, to construct an earthquake occurrence model, it is necessary to first clarify the fault processes and movements that occur deep underground during an earthquake. We try to clarify fault movement processes by investigating the conditions under which a fault starts to move or an earthquake begins to occur, as well as the forces on the fault that result in the fault movement, by reproducing in the laboratory fault movements that occur deep underground. To reproduce processes that occur deep underground in the laboratory, technologies need to be developed to address the difference in environmental conditions and the difference in timescale between the natural world and the laboratory.Temperature and pressure conditions are different deep underground than they are at the ground surface. To reproduce the conditions that prevail underground in the laboratory, it is necessary to develop experimental technologies to reproduce a high-pressure and high-temperature environment and also control for water content. Such an environment can be reproduced by first putting the material to be tested in the experiment into a sealed high-temperature and high-pressure vessel and then applying force to deform the material. This can be achieved by adding a pressure vessel that controls the sample environment to an apparatus based on existing technology in the materials science field.The timescale of many natural phenomena is long; it is impossible to observe even one cycle of a phenomenon such as the occurrence of a mega-earthquake on the human timescale. The progression of the mega-earthquake processes, which is our research subject, is very slow, much longer than a human lifespan. For example, subduction-zone earthquakes such as a magnitude 8 class Nankai Trough earthquake occur at intervals of several hundred years, and a magnitude 9 class mega-earthquake such as the 2011 off the Pacific coast of Tohoku Earthquake occurs at thousand-year intervals. Earthquakes that occur on active inland faults in the Japanese islands may occur at intervals of more than a thousand years. This means that if one wishes to observe the processes occurring during one earthquake cycle, one needs several hundred to a thousand years or more. Here, we apply thermodynamics considerations.[14] From a microscale viewpoint, the progression speed of a process that occurs deep underground is thought to be regulated by the speed of chemical reactions, as will be discussed in the next chapter. Therefore, to observe and investigate in a laboratory setting the progression of a process that progresses extremely slowly deep underground, the progression must be sped up. To do this, it is necessary to develop a high-temperature technology to accelerate the speed of chemical reactions by producing higher temperatures than those that exist in the underground environment where the fault movement actually takes place. We developed our own high-temperature technology for this purpose.4 Scenario for achieving our research aim and the integration of component technologiesFigure 3 shows the overall research flow and the component technologies used in this research. First, a working hypothesis is developed based on observations. The working hypothesis is verified by using methods and techniques that integrate specially developed technologies with existing technology. In this chapter, the component technologies are explained, and in Chapter 5, new concepts resulting from our


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