The strongest earthquakes that strike the planet, such as the 9.0-magnitude earthquake that hit Japan last year, occur at particular "hotspot" points of Earth's crust, a new study finds.
About 87 percent of the 15 largest earthquakes in the last century occurred in the intersection between specific areas on spreading ocean plates, called oceanic fracture zones, and subduction zones, where one tectonic plate slides underneath another, according to the paper, published recently in the journal Solid Earth. The scientists used a data mining method to find correlations between locations of earthquakes over the last 100 years, the strength and geological origin.
The bottom of the ocean is crossed by underwater ridges, such as the mid-Atlantic ridge, which runs north to south between the Americas and Africa. These ridges divide two tectonic plates that move apart as lava emerges, solidifying and creating new rock. The midocean ridge jogs back and forth at offsets known as transform faults, creating zigzag-shaped plate boundaries. Fracture zones are scars in the ocean floor left by these transform faults.
These fracture zones are often marked by large underwater mountains with valleys between them. Millions of years after forming in the middle of the ocean, these mountains slowly advance all the way to a subduction zone, often at the opposite end of the sea. The researchers hypothesize that these submarine mountains "snag" as they enter subduction zones, causing an enormous amount of pressure to build up over hundreds or thousands of years before finally releasing and creating huge earthquakes, according to the study.
Read More Here by Douglas Main
OurAmazingPlanet
Wed, 05 Dec 2012
Wed Dec 05, 2012 7:17 pm