13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- points ", ', ,and "' A A A A is the Pacific Plate on the west. The side with the points , ' , and " C C C is the North American Plate on the east. It was pictured the displacements and the strains experienced at the region before, during and after the earthquake as follows [4]. “Let AOC be a straight line at some early data when the region was unstrained. By 1874-1892, Ahad been moved to 'A andCto 'C , andAOChad been distorted into ' 'AOC ; By the beginning of 1906, A had been further displaced to "A and C to "C , then the sum of the distances " AA and " CC being about 6 meters; andAOChad been distorted into " " A OC .” “When the rupture came, the opposite sides of the fault slipt about 6 meters past each other; A O" andC O" straightened out to " " A O and " " C O ; and the straight lines which occupied the positions " " A O and " " C Q just before the rupture, were distorted afterwards into the lines " " A B and " " C D , these lines being exactly like the lines A O" andC O" but turned in opposite directions.” “The straight lines, which occupied the positions ' ' AO and ' ' CQin 1874-1892, were distorted into " ' A O and " ' C Q in the beginning of 1906; at the time of the rupture their extremities on the fault-line had the same movements as other points on that line; 'O moved to 'B and 'Q moved to 'D.” Subsequently, the elastic rebound theory for the cause of earthquake was developed, established and used by many others. It has been the main stream theory for the past one hundred years. 2.2. Brief description Correspondingly, the existing elastic rebound theory in association with the plate tectonics for the cause of tectonic earthquakes can be briefly described below. The Earth’s crust can be divided into a number of large and/or small tectonic plates. There edges are deep faults. The slow motion of convection currents in the plastic hot material of the mantle drives, pushes and pulls the plates. The tectonic plates can have relative motions in the order of several cm per year. Deep faults with brittle and locked zones can be present in the crust rocks. As the plates move slowly, their fault edges can stay locked, the surrounding crustal rocks can gradually deform for a long time. The elastic stress-strain energy can be built up and stored in rock masses. When the stress on the locked fault zone exceeds its breaking strength, a sudden rupture of the brittle fault part would occur, which causes an earthquake. Its side rocks can abruptly slip into new positions. Such sudden rupture can occur along pre-existing faults or newly formed faults. The larger the earthquake magnitude, the larger the ruptured fault length and the larger the slip offset. They take place at either tectonic plate boundaries or inside plates. So, there are interplate and intraplate earthquakes. The sudden rupture can occur along pre-existing faults or newly formed faults. 2.3. Work and energy The work (W) done at the time of rupture was given by the following equation [4]: W FDA 2 1 = , (1) where F is the force per unit area of the fault-plane, A the area of the fault plane and D the slip. For the 1906 California earthquake, the fault depth was 25 km, the length 435 km, the average shift 4 meters, and the force 1×108 dynes per square centimeter. The work was estimated 1.75×1024 ergs (or 1.75×1017 joules). “This energy was stored up in the rock as potential energy of elastic strain
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