Echo of quake raised the land

Dr Aster, who compiled seismograms to measure the shock waves at increasing distances from the quake’s epicenter, said the waves were 1,000 times the size of those that seismologists customarily measure. The colossal jolt struck December 26 off the west coast of northern Sumatra, and the shock waves radiated out through the earth’s rocky interior, traveling faster than waves do in air or water.

Aster used data gathered by a global network of seismometers run by the Incorporated Research Institutions for Seismology, a consortium based in Washington.

The closest readings came from the Australian Cocos Islands, south of Sumatra, and Sri Lanka, and the farthest from Ecuador. The seismic data show the waves traveling around the earth for six hours. Aster said that even in Ecuador, the shock wave displaced the earth’s surface more than two centimeters, or nearly an inch, but the movement was too slow to be perceptible to humans.

The jolt was much sharper in Pallekele, Sri Lanka, and shook the ground over a range of nearly four inches, he said. The seismogram from Tristan da Cunha, a group of British islands in the South Atlantic, shows the main wave arriving after a little more than an hour, then two smaller ones that circled the earth in two directions arriving after about 120 minutes and 230 minutes. — NYT