HOME > Research Group > Fault and Geodynamics Research Group

Research Group Division of GeoEnvironmental Science

 

Fault and geodynamics Research Group

•Professor Hiroyuki Nagahama,
specializing in Rock fracture mechanics, Earth continuum mechanics, and Earthquake prediction
•Professor Norihiro Nakamura,
specializing in Earth and planetary magnetism studies, Magnetic field, and Meteorites
•Instructor Soichi Osozawa, specializing in Structural geology, Petrology of metamorphic rocks, and Plate tectonics
•Assoc. Professor Jun Muto, specializing in Structural geology, and Experimental rock mechanics
 
 

Investigating earthquakes based on substances in earth faults

Investigating earthquakes based on substances in earth faults How would an earthquake occur and stop? Actually, the seismic waves produced by earthquakes are a source of abundant information, but we can use them in other ways as well. For example, to characterize earth faults, we can dig deep into the earthquake fault using boring techniques or examine the rocks and stones that were once created in the past in the deep underground, but which are now exposed on the ground surface. Regarding the earthquake that occurred in southern Hyogo prefecture of Japan in 1995, and another one in Chi-Chi, Taiwan in 1999, analyses made of rocks and stones of the associated fault using an electron microscope, an EPMA, and an instrument for magnetic-susceptibility measurement indicated to us that the fault surface had been melted by the frictional heat produced by the earthquake.

 

Using such techniques, we can know “what can happen deep underground in the earth fault”. The next step we move to is to conduct an experiment to replicate the effect using various means and techniques that we know of. The equipment by which we can recreate the same level of pressure and temperature that are created as at the deep location as the earthquake occurs is a rock deformation testing machine of a gas medium, high-temperature, and high-pressure. Using this testing machine, we can continuously recording the strength of the stress force, the sliding volume of the fault, and the electro-magnetic signals emitted from the earthquake, for example, uninterrupted synchronous data of 5 MHz on 8 channels are obtainable. Consequently, we can experiment to simulate to an earthquake reoccurrence, and can determine the associated rock destruction and sliding friction as well. According to the experiment results, we recently discovered how a firmly settled object would slide, revealing that no sooner was the melted layer created by the friction heat than it slid less. That interesting phenomenon appeared to contradict common sense.

 

Investigating earthquakes based on substances in earth faults How would we be able to predict an earthquake? Researching electromagnetic waves and light that are emitted from earthquakes is important for earthquake predictions, and is attractive also to understand earthquake mechanisms. Although it might seem unbelievable, even plasma is produced when natural quartz is slid with friction.

 

Recently, we have started the prediction of a possible large-scale earthquake that will occur somewhere offshore of Miyagi prefecture or in the Nagamachi–Rifu line fault zone. Assuming that radon gas is radiated from the earth’s crust as a result of a small deformation on the earth’s crust immediately before an earthquake occurs and the air is ionized. For that reason, pre-earthquake electromagnetic phenomena would be generated. We are conducting observations of radon density in the air inside deep well dug into a deep fault, and also whether any abnormality can be found or not in the electric wave transmission.

 

One reason that it is difficult to solve the problems of earthquake and/or fault is that the earth’s crust is not homogeneous: it includes many defects. To overcome this situation, we are also studying models of gravity and electromagnetic fields using continuum mechanics based on a new gauge field theory resembling the Yang–Mills field.

 

Together with research work on the magnetism of the rocks at earth faults, other research work on electromagnetic phenomena that happen with an earthquake when it occurs is contributing to understanding of planetary science types of phenomena. Some examples of those phenomena are the dynamo activities of the early stage of the earth, the generation of plasma magnetic fields during meteorite collision, and the magnetic field of the primitive solar nebula. Research work of one type often leads in unprecedented directions.
 
 

Investigating plate movements based on fossils and geological features

The oceanic plate sinks from the ocean trench, and the ocean trench accretionary wedge is formed on the edge of the continent; then it is gradually changed to form a continental crust. During this process, the rocks that are created and changed by nature are coming to rise from as deep as several tens of kilometers underground. Phenomena of this type have been steadily elucidated by Instructor Osozawa.