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| At the National Research Institute for Earth Science and Disaster Prevention (1995). |
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As a graduate student at the University of Tokyo, I
studied the structure of tectonic plates--layers of rock about 70 kilometers
in thickness that cover the earth's surface--and the difference between
the destruction caused by small earthquakes and that resulting from major
ones. With so many people working on major quakes, I decided to make a careful
study of small-scale earthquakes. In 1974, I completed a doctoral thesis
on the source of the microearthquakes occurring on the Kii Peninsula in
Wakayama Prefecture and received my Ph.D. I then joined the Science and
Technology Agency's National Research Center for Disaster Prevention, which
later became the National Institute for Earth Science and Disaster Prevention,
and studied topics that could be applied to earthquake-disaster prevention,
particularly patterns of earthquake activity in the Tokyo area.
In order to gain insight into the mechanism of major earthquakes and attempt
to predict them, one needs an accurate understanding of the structure of
the earth beneath us. At the National Research Center for Disaster Prevention,
I carefully analyzed a large amount of data showing the hypocenters where
tremors originated to determine the very complex structure of the earth
beneath the Kanto (Tokyo) and neighboring Tokai districts, an area where
major earthquakes have occurred in the past.
The Kanto-Tokai district is made up of three
overlapping plates. First, we have the Eurasian Plate, on which most of
the Japanese archipelago is situated. The Philippine Sea Plate, which supports
the Izu Peninsula, is slowly slipping under the Eurasian plate as it moves
from southeast to northwest. And beneath that, the Pacific Plate is moving
from east to west. Japanese seismologists had offered up a number of competing
models to describe the arrangement and movement of tectonic plates in the
area, but none of them was viewed as the final word on the subject. However,
the "Ishida model," as mine was known, was constructed by locating the hypocenters
of 40,000 tremors of magnitude 1 or more, and it was soon regarded in seismological
circles as the definitive model.
In recognition of this work, I was awarded the Saruhashi Prize for women
scientists in 1989, and in 1995 I was chosen as the first woman to chair
the Seismological Society of Japan. |
