Figure 3.1 illustrates a Japanese traditional idea on causative mechanism of earthquakes. Therein a cat fish whose movement underground caused an earthquake and destroyed present Tokyo in the middle of nineteenth century are punished by angry people. The true understanding of the cause of earthquakes started in the second half of the twentieth century.
It is commonly understood today that an earthquake is caused by a rupture of a fault in the earth’s crust. Figure 3.2 shows various fault movements: normal, reverse, and (left- or right-lateral) strike-slip. The normal fault is caused by tensile stress field because the two earth blocks in Fig. 3.2 are separated from each other. In contrast, the reverse fault is generated by compressional stress field. This is the case in the subduction zone where an ocean tectonic plate subsides under a continental plate.
As for terminology, an earthquake hypocenter or focus stands for the place of the first rupture, whilst an epicenter is the place at the surface that lies just above the focus. See Sect. 5.10.
KeywordsSubduction Zone Plate Boundary Continental Plate Fault Movement Slow Slip Event
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