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Graphical Abstract
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Abstract
The seismicity pattern of China, especially that seen in North China is. described in this paper. Strong earthquakes with magnitudes of M≥7.5 are found to occur at certain definite intervals of distance. In North China, recent earthquakes with magnitudes M≥7.0 occurred within a belt in the form of a stripe. The seismicity immediately before the strong earthquakes show a similar distribution pattern. The strong earthquakes of given separate regions are thus obviously correlatable. Such a correlation can neither be shown to be due to a process of propagation nor be explained by the assumption that correlatable earthquakes are linked by faults. It is thought to be possibly the result of the action of an ambient stress field over a broad region. Medium and small shocks, whose numbers maintain certain constant ratios, are usually observed as preludes to the strong earthquakes.All of these facts may be considered to be the results of buckling of crustal layers under an ambient stress field. According to this view-point, we are able to calculate the values of b: equalling 0.75 for average earthquakes; 1.5 for volcanic earthquakes, reservoir earthquakes and some earthquake swarms; and 0.5 for earthquakes on the same fault system. These figures agree rather well with actual observations, so the discussion presented here might have some general significance.
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