Vol.9 No.2 2016
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Research paper : Development of rock deformation techniques under high-pressure and high-temperature conditions (Koji MASUDA)−100−Synthesiology - English edition Vol.9 No.2 (2016) composing the fracture process mechanism, in constructing a physical model of the process, and in verifying the model. A laboratory experiment does not re-create in miniature fault movement that occurs in the natural world, so it is important when designing laboratory rock experiments to determine how natural and laboratory conditions differ (Fig. 2). For example, they differ with respect to size, timescale, and structure. The size difference is the difference in spatial scale at which the process occurs. Do processes that occur in rock samples in the laboratory exactly reproduce the wide-ranging fault movement and deformation/fracture processes that occur in nature? Experimental results have shown that the fracture strength of a rock differs according to the size of the sample. In natural fault movements, it is known that some properties of the movement are dependent on the fault size and others are not. While it may be relatively straightforward to replicate and study properties that do not depend on spatial size in the laboratory, the size-dependent properties must also be studied to determine how they change with size; then, to interpret the natural processes, the laboratory results must be extrapolated to the natural scale. The friction law on which current computer simulations of earthquakes are based was determined mainly from rock experiments conducted in the laboratory, but it has been clearly shown that the frictional properties of rocks differ depending on the area (spatial size) of the contact surface.[9]Another important difference is the difference in timescale between the natural world and the laboratory. In the natural world, earthquake-related processes normally progress extremely slowly. Because the occurrence interval of earthquakes that cause major disasters is several hundred to a thousand years, we cannot replicate the progression of the processes involved at the same speed. In this paper, I report an example of an experiment in which these processes are accelerated. Also, the natural materials of a fault zone are not uniform; both the materials and their structural features are complex. What plays the main role in fault movements? For example, in a fault zone composed of several types of materials, does one material dominate the overall fault movement? Where does the movement occur? The properties of the material that occupies the most space in terms of volume percent does not necessarily dominate the fault movement process. If slip or movement occurs dominantly in a particular fault zone stratum, then the properties of that stratum, though it may account for a low percentage of the materials in the fault zone, must be investigated carefully to learn how and why the fault movement occurs. Thus, the aim of rock experiments in the laboratory is not to imitate the natural world, but to extract and investigate the essential mechanism of fault movement. 2 History of the development of rock experimental technologyFor the rock experiments in the laboratory, von Karman first developed a deformation testing device using hydrostatic pressure in the 1910s; Griggs succeeded in developing a modern experimental apparatus for rock deformation experiments in the 1930s; and researchers such as Handin Fig. 1 Flow chart of earthquake forecast research and the position of high-temperature and high-pressure rock deformation experiments in the overall research schemeTo forecast earthquake occurrences, it is necessary to correctly understand the earthquake occurrence mechanism, to construct a physical model of earthquake occurrence, to develop a numerical model of earthquake processes, including those leading up to earthquake occurrences, and to replicate them in a computer simulation. High-temperature and high-pressure rock deformation experiments contribute to the refinement of the earthquake occurrence model by providing knowledge that can be used to determine the constitutive equation and its parameters, as well as by verifying the physical model.Fig. 2 Fault zones in the natural world and faulting in a laboratory rock experimentLeft: Occurrence zones of a subduction zone earthquake (A) and an inland earthquake (B) caused by plate subduction. The arrows show the direction of fault slip. Inland earthquakes are also caused by other types of slip such as normal faults and lateral faults. Right: A cylindrical rock sample used to reproduce faulting in a laboratory experiment. Rather than trying to exactly replicate fault movement in the laboratory, the important aims of a rock experiment are to determine the factors that dominate the processes and mechanisms of natural fault movements, to construct a physical model on the basis of these factors, and to verify the model.Laboratory rock experimentNatural worldExtract and verify factors that dominate the mechanism and process(A)(B)Earthquake forecastModel refinement, physical law, parametersSuccessive incorporationPast records and factsHigh-temperature high-pressure rock deformation experimentObservation data (current state and activities)Earthquake research based on geology History of active fault activities Survey of tsunami depositsSimulation based on the numerical modelConstruct a physical model of earthquake generationUnderstand the earthquake generation mechanismImprove forecast precisionMitigate earthquake disaster

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