Name : TSUKUDA,  Tameshige
            Position : Associate Professor
            Division/Center : Earthquake Observation Center
            Research Area : seismicity, seismotectonics, earthquake prediction
 
 

Research :

       My group's main concern is earthquake prediction based on microseismicity, seismotectonics and crustal activities. The accumulated
       seismicity data are analyzed to deduce temporal changes of various parameters related to the crustal activities. Such phenomena as
       quiescence, formation of seismic gap, surrounding active seismicity, earthquake swarms, and nucleation of precursory shocks close to
       impending large earthquakes are being studied. The data from seismological and geophysical observatories attached to the
       Earthquake Observation Center, Earthquake Research Institute, are available.

       Recently, the 1995 Hyogo-ken Nanbu earthquake brought us a large volume of information on anomalous phenomena before and after
       the disaster, such as rumbling noise, groundwater changes, luminous phenomena, abnormal behavior of animals, and so on. There
       seems to exist even now a large volume of uncovered information among local residents. We have some items to be tested by a
       scientific approach such as earthquake lights, which are probably related to emmissions of electric charges and inonized gasses, and
       groundwater phenomena, the data from which provide us with direct information from under the ground.

       The importance of such field research as questionnaire and interview surveys is equal to that of modelling and laboratory experiments
       to explain and reproduce the anomalous phenomena. The results obtained from the field research should constrain approaches to
       modelling. We have reports based on people's experiences through their five senses and through natural groundwater wells or
       devices attached to life line facilities. The electrical and strain data from nearby observation stations of Kyoto University are also
       available.

       We disclosed more than 23 coseismic light sources distributed as wide as 50km in radius from the epicenter of the earthquake. They
       are classified into four types and three color tones. Size, height, and luminance are estimated for some sources. There have been no
       quantitative reports on the luminous sources.

       We have some reports of luminous phenomena before the earthquake. The occurrence times range from within several hours to about
       10 hours. A sustained brightness in the sky was observed over the Miki city several hours before the quake. Searches for other
       eyewitnesses continue.

       An eruption of groundwater was estimated to have occurred at the Akashi Strait, which started two days before the quake, based on
       the report of the appearance of brownish-black sea water by captains of ferry boats. To interprete groundwater changes, such as rise
       of groundwater temperature and water becoming cloudy for a day after the quake, we are conducting continuous temperature
       measurements, analyzing ingredients, together with laboratory experiments in cooperation with Niigata University and Shinshu
       University. Impulsive water temperature changes with a duration of several hours with an increase of 2-4 degrees centigrade at the
       Arima Hot Spring, Kobe, is a subject related to underground dynamics to be studied. The measurements of electric potential at a well
       to detect a current in the water are designed to investigate electro-chemical processes in the natural state of groundwater flow.

       The electric potential of a tree was also tested in relation to such artificial sources as high-voltage power lines, which will provide
       hints for understanding the responses of plants and animals to earthquake disturbances.

       A rumbling sound is generated by the vibration of ground at the time of an earthquake. People sometimes reported that they clearly
       detected the sound before a strong motion. Experiments to confirm the efficiency of energy transformation from ground motion to air
       pressure have been conducted at Niigata and Shizuoka in cooperation with an audio consulting company. A linear transformation is
       achieved at a low frequency range less than several tens of Hertz. On the contary, higher frequency sounds seem to be generated with
       non-linear processes around the ground surface. Confirming sonoluminescence at the time of a large earthquake is one of the
       purposes of this audio-monitoring project.
 

Publications :

    1.Hiramatsu, Y., M. Ando, T. Tsukuda and T. Ooida, Three-dimensional image of the anisotropic bodies beneath central Honshu, Japan,
       Geophys. J. Int., 135, 801-816, 1998.
    2.Tsukuda, T., Sizes and some features of luminous sources associated with the 1995 Hyogo-ken Nanbu earthquake, J. Phys. Earth,
       45, 73--82, 1997.
    3.Kitagawa, Y., N. Koizumi and T. Tsukuda, Comparison of postseismic groundwater temperature changes with earthquake-induced
       volumetric strain release: Yudani hot spring, Japan, Geophys. Res. Lett., 23, 3147--3150, 1996.
    4.Mikumo, T., K. Hirahara, F. Takeuchi, H. Wada, T. Tsukuda, I.Fujii and K., Three-dimensional velocity structure of the upper crust in
       the Hida region, central Honshu, Japan, and its relation to local seismicity, Quaternary volcanoes and faults, J. Phys. Earth, 43, 59-78,
       1995., J. Phys. Earth, 43, 59--78, 1995.