By far, the most destructive tsunamis are generated from large, shallow earthquakes with an epicenter or fault line near or on the ocean floor.  These usually occur in regions of the earth characterized by tectonic subduction along tectonic plate boundaries.

    The high seismicity of such regions is caused by the collision of tectonic plates.  When these plates move past each other, they cause large earthquakes, which tilt, offset, or displace large areas of the ocean floor from a few kilometers to as much as a 1,000 km or more.  The sudden vertical displacements over such large areas, disturb the ocean's surface, displace water, and generate destructive tsunami waves.

    The waves can travel great distances from the source region, spreading destruction along their path. For example, the Great 1960 Chilean tsunami was generated by a magnitude 9.5 earthquake that had a rupture zone of over 1,000 km.   Its waves were destructive not only in Chile, but also as far away as Hawaii, Japan and elsewhere in the Pacific.  It should be noted that not all earthquakes generate tsunamis.  Usually, it takes an earthquake with a Richter magnitude exceeding 7.5 to produce a destructive tsunami.
   海啸是一种具有强大破坏力的海浪。水下地震、火山爆发或水下塌陷和滑坡等大地活动都可能引起海啸。

   地震发生时，海底地层发生断裂，部分地层出现猛然上升或者下沉，由此造成从海底到海面的整个水层发生剧烈“抖动”。这种“抖动”与平常所见到的海浪大不一样。海浪一般只在海面附近起伏，涉及的深度不大，波动的振幅随水深衰减很快。地震引起的海水“抖动”则是从海底到海面整个水体的波动，其中所含的能量惊人。海啸时掀起的狂涛骇浪，高度可达10多米至几十米不等，形成“水墙”。另外，海啸波长很大，可传播几千公里而能量损失很小。由于以上原因，如果海啸到达岸边，“水墙”就会冲上陆地，对人类生命和财产造成严重威胁。
1.the encyclopedia of earth.

2.百度知道。