13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- immediately before the rupture; when the rupture occurred, it was transformed into the kinetic energy of the moving mass, into heat and into energy of vibrations; the first was soon changed into the other two. When we consider the enormous amount of potential energy suddenly set free, we are not surprised, that, in spite of the large quantity of heat which must have been developt on the fault-plane, an amount was transferred into elastic vibrations large enough to accomplish the great damage resulting from the earthquake and to shake the whole world so that seismographs, almost at the antipodes, recorded the shock.”[4] Modern seismology has adopted the fault rupture and/or slip model in the quantitative analysis of seismic waves [5]. A quantitative measure of the size and strength of a seismic shear source is the scalar seismic moment M0 with the unit Nm (or Joule). M0 is a measure of the irreversible inelastic deformation in the rupture area and can be expressed as follows [5]: DA μ = 0M , (2) where μ the rigidity or shear modulus of the rock mass, Dthe average final displacement after the rupture, A the surface area of the rupture. M0 has the following relations with the surface-wave magnitude scale MS (or the moment magnitude MW) and the radiated seismic strain energy ES (Joule): log M 1.5M 9.1 S 0 + = , (3) S S log E 4.8 1.5M = + (4) Furthermore, the total energy release ET can be expressed by: f S TE E E = + , (5) where Ef is the friction energy to power the growth of the earthquake fracture (Efracture) and the production of heat (Eheat). The ratio ES/ET (i.e., the seismic efficiency) is perhaps only about 0.01 to 0.1, depending both on the stress drop during the rupture as well as on the total stress in the source region. In other words, only a small fraction of ET goes into producing seismic waves. For instance, the 2011 off the Pacific Coast of Tohoku Earthquake may have MW = 9.0, Mo = 4.5×10 22 Nm, and ES = 2.0×10 18 Joule. The 2001 Kunlun Pass W. Earthquake may have MS = 8.1, Mo = 1.8×10 21 Nm, and ES = 8.9×10 16 Joule. 3. Observations and Comments Based on the above brief, the existing elastic rebound theory for the cause of earthquakes looks quite simple and straightforward. Accordingly, the classical theories of elasticity, elastodynamics, fracture mechanics and plasticity have been extensively applied to mechanically examine the mechanism of earthquakes and to quantitatively predict the earthquakes since the crustal rocks and soils can be considered as solid materials [5, 11, 12]. Furthermore, the monitoring, testing and modeling techniques and methods have been rapidly developed and used. A huge amount of accurate data such as GPS, satellite images and seismographs have been monitored and measured for the movement of tectonic plates and faults. Hence, if the elastic rebound theory had been correct or along the right track, the movement and deformation of the massive solid rocks and soils associated with the tectonic plates and faults would have had many regularities and phenomena following the guidance of the classical theories of solid mechanics. The earthquake unpredictable statement would not have become a mainstream consensus in modern seismology and seismo-geology. However, many devastating damage earthquakes still occurred suddenly without pre-warning or pre-notice by human beings. Recent examples are the 2008 Wenchuan Earthquake [1] and the 2011 off the Pacific Coast of Tohoku Earthquake [13-15].
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