Today, the Pacific Ocean continues to open along the East Pacific Rise, which runs from the edge of the Antarctic Plate to the Sea of Cortez. West of this mid oceanic ridge, the Pacific Plate is moving to the northwest while, to its east, the Cocos and Nazca Plates are moving eastward; these latter plates are remnants of the oceanic Farallon Plate which once stretched along the western coast of the Americas.
Encountering the west edge of the South American Plate, the Nazca Plate is forced to subduct, creating an offshore trench and giving rise to the volcanic range of the Andes. Friction along this line of subduction drags down the edge of the South American Plate and, when this pressure is suddenly released, an earthquake results. This morning's 8.8 magnitude quake, off the Chile coast is expected to produce a significant tsunami across the Pacific as the overlying ocean was pushed upward by the rebounding plate. Traveling over 500 miles per hour, the tsunami wave is expected to reach Hawaii by 11 AM local time and may eventually affect all islands and coastal regions of the Pacific Rim.
The Philippine Plate, a diamond shaped piece of crust off the southeast coast of Asia, is being pushed westward by the advancing edge of the Pacific Plate. Along its southwest margin, the Philippine Plate is subducting beneath the Eurasian Plate to produce the Philippine Islands while, along its northwest edge, it is subducting beneath the Eurasian Plate to form the southern and central islands of Japan. Both of these island clusters, like the Andes, are volcanic in origin, produced by melting along the edge of the subducting plate, and, like Chile, both archipelagos are prone to earthquakes and tsunami events; southern Japan's 7.0 quake, some 900 times weaker than Chile's, also developed along a subduction trench. While not directly related to the same fault system, this week's earthquakes in Chile and Japan were both secondary to ocean floor spreading along the East Pacific Rise.
