Geophysics

We, the people in the 21st century, are facing problems on subsurface (crust of the Earth) including development of energy resources, utilization of underground spaces and preservation of the Earth's environment. A doctor of the Earth with "eyes looking inside the Earth" and "arms sensing inside the Earth" can help solve these problems.

We are studying geophysical prospecting methods that can look and feel inside the Earth. They utilize the physical phenomena such as seismic wave, electrical current and electromagnetic wave and measure the Earth in a nondestructive way from remote places.

Geophysical prospecting is interdisciplinaly. It is based on geophysics and has a close relation to many fields both in science and in engineering including geology, resources engineering, electronics and so on. It is a "Informatics on subsurface".

Academic Staff

Hitoshi MIKADA

Hitoshi MIKADAProfessor (Graduate School of Engineering)

Research Topics

We set our scientific target to explore subsurface structure of seismogenic and volcanic active regions with respect to their geohazardous activities and to earth resources. It is, therefore, necessary to look into state-of-the-art methodologies, including scattering and attenuation of elastic waves through crustal medium, application of new technologies for exploration-demanding regions, single well imaging techniques, integration of data from multiple survey means, and the enhancement of various signal processing schemes.

Contacts

Room 112, Bldg. C1, Katsura Campus
TEL: +81-75-383-3196
FAX: +81-75-383-3198
E-mail: mikada@gakushikai.jp
http://tansa.kumst.kyoto-u.ac.jp/tansa/people/mikada/

Junichi TAKEKAWA

Junichi TAKEKAWAAssistant Professor (Graduate School of Engineering)

Research Topics

It is essential to reveal mechanical and engineering behavior of rock mass for development of earth resources, earthquake disaster prevention and global environment protection. I study failure phenomenon occur in connection with seismic wave propagation, fluid flow occur in connection with failure phenomenon by using numerical approach.

Contacts

Room 111, Bldg. C1, Katsura Campus
TEL: +81-75-383-3197
FAX: +81-75-383-3198
E-mail: takekawa@tansa.kumst.kyoto-u.ac.jp

Research Topics

Shallow subsurface survey using geophysical prospecting methods for infrastructure and geo-environment

It is not easy to delineate the geological condition and the physical properties of soil and rock even in the very shallow subsurface. Only geophysical methods can understand the 3-D distribution of underground water and contaminator in the soil from the surface as well as geological structures.

We are applying the geophysical prospecting methods to the shallow subsurface survey that is inevitable for maintaining the infrastructure and geo-environment. The application includes;

  • Prediction of a head of the tunnel face using seismic method,
  • Detection of cavities located inside the river bank using shallow S-wave reflection method,
  • Detection of buried pipes and estimation of its material properties using ground penetrating radar,
  • Monitoring soil improvement treatment and environmental remediation using geophysical methods.

Figure 1 shows an application of seismic technique to prediction of a head of tunnel face. Two seismic reflectors imaged here show the geological boundaries. Using this information, we can predict the location, direction, dip and physical properties of sudden change of geological condition, prior to excavation.

image : Geological boundaries imaged using seismic reflection survey of a head of tunnel face.
Figure 1. Geological boundaries imaged using seismic reflection survey of a head of tunnel face.
(a) Schematic, (b) the result of 3-D imaging and (c) the estimated geological boundaries.

Deep subsurface survey using geophysical prospecting methods for the exploration and the development of new energy resources

It is not too much to say that the fossil energy such as oil and natural gas does support the industrial development of the 20th and 21st centuries. Without geophysical methods, we can never explore nor develop these energy resources located deep (over several 1000 meters) inside the Earth. Three-dimensional seismic reflection technique can visualize complicated 3-D subsurface structures such as faults and folds, understand the ancient sediment environment and reveal the complete history of the sedimentation.

We are applying the geophysical methods to a new challenging target for exploring and developing new energy resources. The target includes;

  • Exploration and production monitoring of methane hydrate existing beneath the deep sea floor or the permafrost,

  • Monitoring oil sand recovery during steam injection,

  • Monitoring CO2 sequestration into coal seams and recovery and production of methane gas from the coal seams.

Figure 2 shows a 3-D data volume of subsurface structure obtained by 3-D seismic reflection method. We can extract any sections of interests and can calculate physical properties from the data volume.

image : Data volume of subsurface structure obtained by 3-D seismic reflection method.
Figure 2. Data volume of subsurface structure obtained by 3-D seismic reflection method.

Developing a high-resolution visualization technique of subsurface information (geotomography) and its application

Technologies such as X-ray CT and MRI in medical diagnostics can visualize a section or even a 3-D image of human body without cutting it. Geotomography is based on the same principle. Lots of sensors are arranged to encompass a target area. The measured data are processed by a extensive use of computers. Then we can obtain beautiful color images of the distribution of seismic velocity, attenuation characteristics and resistivity. Imaging 3-D distribution can also be possible.

We are studying geotomography techniques from the basic theory to the application to the following targets.

  • High resolution imaging of fractured zone using waveform inversion technique,
  • Monitoring the effects of environmental remediation treatment using resistivity tomography,
  • Imaging 3-D distribution of a fault zone at a dam construction site using 3-D seismic tomography.

Figure 3 shows the 3-D velocity distribution obtained by using 3-D seismic tomography. The upper figure shows the velocity distribution of the volume encompassed by the 4 boreholes. The lower figure shows the 3-D distribution of the fractured zone in a rock mass at another site.

image : 3Three-dimensional velocity distribution obtained by using 3-D seismic tomography.
Figure 3. Three-dimensional velocity distribution obtained by using 3-D seismic tomography.

Laboratory Website

http://tansa.kumst.kyoto-u.ac.jp/