Published: March 12, 2007 at 8:39 AM Scientists study May's Tonga earthquake 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...