ST. LOUIS, March 12 (UPI) -- A U.S.-led team of seismologists says it has determined why last May's major earthquake in Tonga did not cause a large tsunami.
Professor Douglas Wiens at Washington University in St. Louis and colleagues in Australia, Japan and Tonga said although a Pacific Rim tsunami warning was issued following the May 3, 2006, magnitude 8.0 quake, the resulting tsunami was very minor and caused no damage.
Tsunamis generally result from shallow-thrust earthquakes, which occur when the seafloor is pushed downward beneath the land in places like Japan, Chile, Indonesia and Mexico. The researchers found the May earthquake was, instead, a slab-tearing event that ruptured the down-going seafloor beneath Tonga. That, said the scientists, explains why the tsunami was smaller than expected, and suggests large earthquakes in Tonga may typically be of the slab-tearing variety, consistent with the lack of large historical tsunamis in Tonga.
Wiens and graduate student David Heeszel presented the study in December during the winter meeting of the American Geophysical Union in San Francisco.
