Poster of the Hawaii Earthquake of 15 October 2006 - Magnitude 6.7
The Island of Hawaii is the youngest island in a chain of volcanoes that stretches about 3500 miles across the northern Pacific Ocean. The island chain results from a magma source that originates deep beneath the crust. The ocean crust and lithosphere above the magma source, within the Pacific tectonic plate, move to the northwest with respect to the deep magma source. Over millions of years, new island volcanoes are formed and older volcanoes are carried away from the magma source, erode, and eventually subside beneath sea level.
The 15 October earthquake is probably not directly related to future volcanic eruptions. Non-volcanic Hawaiian earthquakes reflect the long-term accumulation and release of lithospheric stresses, rather than short-term processes associated with the motion of magma before or during an eruption. The long-term stresses consist in part of stresses generated in the crust and mantle by the weight of the volcanic rock that composes the islands. In that sense, most Hawaiian earthquakes that are not directly associated with eruptions are nonetheless broadly related to volcanic activity.
Earthquakes on the volcanic Island of Hawaii are not rare. The largest on record was the magnitude 7.9 1868 earthquake near the south coast which triggered a tsunami that drowned 46 people and which spawned numerous landslides that resulted in 31 deaths. A magnitude 6.9 tremor on August 21, 1951, damaged scores of homes on the Kona coast and triggered numerous damaging landslides.
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