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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