National Geographic : 1995 Jul
Deadly movement of a minor fault A ragged gash that tore through terraced rice fields on Awaji Island (right) revealed the disaster's culprit: the Nojima Fault. The earth quake, which registered 6.9 on the moment mag nitude scale, took 5,500 lives, displaced 300,000 people, and caused at least 100 billion dollars' worth of damage. It was Japan's worst quake since one measuring 7.9 that hit Tokyo and Yoko hama in 1923, killing 143,000. As soon as the shaking stopped, geologists fanned out to look for the source. The fault rupture was found the next morning by a Hiroshima University team led by Takashi Nakata, who had been alert ed by displaced stone steps leading to a lighthouse. "We're in a period of increased seismic activity in Japan," says Nakata. "This was a big one, coming after a calm period of 50 years." When plates of earth's crust col lide, one can be forced beneath the other, creating a subduction zone (1). The Eurasian and Philip pine Sea plates meet obliquely (2), which places a lateral strain on the overriding Eurasian plate. When that plate ruptures (3) along the Median Tectonic Line, it puts a strain on the crust behind it, which develops a new fault zone (4) along the Arima-Takatsuki Tectonic Line.