Name : KAWAKATSU,  Hitoshi
            Position : Professor
            Division/Center : Ocean Hemisphere Research Center
            Research Area : Seismology
            homepage :  http://gachon.eri.u-tokyo.ac.jp/~hitosi/
 
 
 
 

Research
 
 

       Seismological study of the Earth's deep interior
       In the past several years, Fenglin Niu (now at Carnegie Institution of Washington) and I have been investigating the detailed
       structure of the mantle transition zone discontinuities. We utilize a large number of seismic array data to enhance and detect weak
       signals of converted (or reflected) phases at those discontinuities. Our contribution in this field is unique in a sense that we have
       found lines of seismic evidence for the presence of discontinuities below the 660km-discontinuity (Kawakatsu and Niu, 1994; Niu and
       Kawakatsu, 1996). The result for the Indonesian is indisputable, and shows strong evidence for the presence of the mid-mantle
       discontinuities, above which high velocity anomaly can be seen in tomographic models(Niu and Kawakatsu, 1997; Vinnik, Niu and
       Kawakatsu, 1998). The physical origin and geodynamical significance of the mid-mantle discontinuities are the current theme of our
       investigation.

       Broadband seismometry at active volcanoes
       It has been known that there is a lack of information in the geophysical monitoring of active volcanoes. In the conventional
       seismometry, the period range between 1 and several 100 seconds has not been monitored at most volcanoes of the world. To cover
       this period range, we have installed portable broadband seismometers at several active volcanoes. Among them Aso volcano
       constantly emits unusually long-period (15sec) seismic signals. By analyzing those data, we have detected a hydrothermal reservoir
       beneath the active crater. We have also detected "very long-period" signals few minutes prior to phreatic eruptions(Kaneshima,
       Kawakatsu et al., 1996). In the future these signals would be used to give immediate warnings for eruptions. More recently we have
       detected a crack-like conduit beneath the crater (Yamamoto, Kawakatsu et al., 1999). We believe that these studies are among the
       best seismological studies ever conducted at active volcanoes. Co-investigators: Satoshi Kaneshima (Tokyo Institute of
       Technology), Takao Ohminato (ERI), Yasuaki Sudo (Kyoto Univesity).

       Realtime monitoring of the earthquake activity field
       Our moment tensor solutions for world's major earthquakes (M>5.5) are now well known as "ERI AutoCMT solutions", which are
       distributed to more than 200 researchers of the world (Kawakatsu, 1995). We have also developed automated moment tensor
       determination systems for regional scale (whole Japan) and local scale (Kanto area) problems, and solutions are also distributed to
       the community. Recently we realized that it should be possible to monitor in realtime the long-period (>10sec) wavefield to infer
       corresponding seismic activity field (i.e., earthquakes when they occur) (Kawakatsu, 1998, BERI). This system may eventually let us
       predict strong motion wavefield almost in realtime, base on data from a sparse local scale broadband network.

Publications:

Kawakatsu, H. and F. Niu, Seismic Evidence for a 920km discontinuity in the mantle, Nature, 371, 301-305, 1994

Kawakatsu, H., Automated near-realtime CMT inversion, Geophys. Res. Lett., 22, 2569-2572 1995.

Kaneshima, S., H. Kawakatsu, H. Matsubayashi, Y. Sudo, T. Tutui, T. Ohminato, H. Ito, K. Uhira, H. Yamasato, J. Oikawa, M. Takeo, T. Iidaka, Mechanism of Phreatic Eruptions at Aso Volcano Inferred from Near-Field Broadband Seismic Observations, Science, 273, 642-645, 1996.

Kawakatsu, H.,, On the realtime monitoring of the long-period wavefield, Bull. Earthquake. Res. inst., 73, 267-274, 1998.

Kawakatsu, H., S. Kaneshima, H. Matsubayashi, T. Ohminato, Y. Sudo, T. Tutui, K. Uhira, H. Yamasato, H. Ito, D. Legrand, Aso-94: Aso seismic observation with broadband instruments, J. Vol. Geothermal Res., 101, 129-154, 2000.