TSUNAMIS When they reach the coast, the huge oceanic waves produced by a large or great earthquake rise to an enormous height; such tsunamis can cause severe destruction of coastal regions. Not all earthquakes produce tsunamis. The generation of a tsunami requires the fulfilment of three conditions: (i) a great earthquake in the sea in the subduction zone, (ii a shallow earthquake 50 kilometres), and (ii) an earthquake generated by thrust faulting. Under such conditions, the thrust movement of the seafloor causes waves with a large wavelength. This wave may be just a metre high in the mid sea, but when it reaches the coast, the amplitude increases to 5 to 15 metres, depending on the rupture length or the wavelength l depth of the water column in the mid sea. The most recent experience of the devastating effects of a tsunami in south Asia was the 20o4 Andaman-Sumatra megathrust arthquake (Mw 9.3) (Fig. 14), and the 2011 Japan megathrust earthquake (M 9,0) (Table 3). The 20o4 tsunami took unprecedented numbers of lives, while the 2011 tsunami destroyed the Fukushima nuclear power plant