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| The most energetic seismic
swarm ever recorded struck 150 km south of Tokyo (and 60 km south
of Japan’s Izu peninsula at top left of image) during June-August
2000, with 7,000 magnitude > 3 and five magnitude >
6 shocks (black disks proportional to magnitude). The swarm was accompanied
by several steam and debris eruptions of Miyake volcano (center right),
which was evacuated. Toda et al. argue that the swarm was triggered
by a change in the rate at which the surrounding crust was stressed
by the continuous opening of a massive dike, or vertical blade of
rising magma located beneath the dense line of earthquakes. Calculated
stressing rate changes (warm colors denote increases, cool colors
are decreases) are draped over the bathymetry, with coastlines in
brown. Topography from GSI, bathymetry from JODC, seismicity from
ERI, and imagery by Serkan Bozkurt (USGS) and Shinji Toda (AFRC). |
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