Geography Reference
In-Depth Information
Figure 20. Relative seismic activity (white) and quiescence (gray) at one year intervals
before the Tohoku event (grid size 0.2×0.3º, 3.5≤
M
≤6.5). Circle marks the pending
Tohoku earthquake.
This indicates that the mechanism of a ―seismic gap‖ has set into action.
This effect was described in literature, including in Japanese publications [55],
as a basic model predicting many large earthquakes. Moreover, the epicenter
falls on the border of the quiescence zone, where the gradient between high
and low relative total energy is the largest (rightmost map in Figure 20). This
confirms our earlier idea [56] inferred from data of the Baikal rift zone that the
largest earthquakes occur on the edge of negative seismicity anomalies at the
points of maximum gradient of relative total energy. The gradient map clearly
shows distinct positive anomalies between the pending Tohoku event and its
foreshock, as well as in the area where the earthquake of April 11, 2011 was to
occur on the Ibaraki-Fukushima coast (Figure 21b). The gradient calculation
procedure we are using searches the maximum relative energy difference
between the current and neighbor cells.
Figure 21. The map of relative energy gradients: a) for background seismicity; b) for
seismic activity over a year prior to the Tohoku event (grid size 0.1×0.2º, 3.5≤
M
≤6.5;
aftershocks are removed). Circles and white arrows mark the location of pending
Tohoku earthquake (1), its Miyagi-oki foreshock (2), and an earthquake of 11.04.11
that occurred a month after Tohoku (3).
