Caltech geologist Kerry Sieh used to describe the Sumatran subduction zone that sits off the Indonesian island’s west coast as a place that is tucked away in a corner of the world that just doesn’t have a lot of scientific traffic.
Not anymore. The subduction zone was the location of the December 26, 2004 earthquake that, with the tsunamis it generated, resulted in 300,000 dead or missing Indonesians. And now scientists from around the world are paying it plenty of attention.
The December quake, estimated to have had a magnitude as high as 9.3, originated along the boundary between the Indian/Australian and Eurasian tectonic plates, which arcs 5,500 kilometers (3,400 miles) from Myanmar past Sumatra and on toward Australia. Near Sumatra, the plates meet 5 kilometers (3 miles) beneath the sea at the Sumatran Trench, on the floor of the Indian Ocean. At the trench, the Indian/Australian plate is diving into the earth’s interior and being overridden by Southeast Asia. For more than a decade, Sieh has studied this fault zone, studying coral growth that measures the rise and fall of sea level changes, and installing an array of Global Positioning Satellite (GPS) stations that measure the deformation of the earth.
Now until June 10, Sieh and field technician John Galetza and their Caltech associates are back in Sumatra. Along with Danny Natawidjaja of the Indonesian Institute of Science (Sieh’s former graduate student and the coleader of the expedition), Natawidjaja’s associate Bambang Suwargadi, and other Indonesian colleagues, the team will be taking measurements of the uplift and submergence caused by the earthquakes, and educating locals to the danger roiling under their feet. Here Sieh shares, via e-mail, his personal observations and preliminary scientific findings.
Thursday, May 26, 2005
