Caltech senior research assistant John Galetzka traveled to Banda Aceh six weeks after the earthquake and tsunami leveled the city. At a government operations center he noticed a sign that said that 950 bodies had been discovered that day. “It was a shell of a city,” he says.

After the Tsunami

By Mike Rogers

The signs of catastrophe became evident slowly. On a boat heading up the Indian Ocean toward Banda Aceh along the northwest coast of Sumatra, Caltech senior research assistant John Galetzka first noticed a hospital ship anchored in the ocean. Next he saw a few enormous U.S. Navy ships off shore and many helicopters shuttling back and forth to the mainland. Looking toward land, he began to see an unnatural brown band snaking along the entire coastline. The sienna-colored strip seemed to rise as high as a small building, and as the boat got closer to shore, he could make out masses of broken trees and branches, chunks of concrete, pieces of lumber, twisted metal, plastic detritus, clothing, and other debris clogging the beach.

Maps were useless. The December 26 tsunami that struck western Sumatra following the 9.0 megathrust earthquake in the region had dramatically altered the island’s shoreline. To navigate, the captain of the boat ferrying Galetzka and three colleagues from the Indonesian Institute of Sciences followed a local fishing vessel up a river to the center of the city. It was February 6, six weeks after the disaster that had killed an estimated 300,000 people in several countries bordering the Indian Ocean, but by the look of the battered landscape, the calamity could have happened the day before.

The devastation continued for a mile or two up the river, Galetzka says. “Everything was completely flattened except for a few very strong structures. You could see dump trucks and bulldozers clearing rubble of all sorts. Smoke was rising from burning piles of rubble. People were salvaging metal. There were others in haz-mat suits. It was a surreal scene.” Like the scientists, the ship’s crew was mesmerized by the destruction, and when the ship ran aground on a sand bar, Galetzka noticed that the captain was still steering, too transfixed by what he was seeing to notice that his ship was stuck.

Galetzka had been sent to Aceh Province by his colleague Kerry Sieh, Caltech’s Sharp Professor of Geology, who for more than 10 years has been traveling to Indonesia to study the Sumatran plate boundary, with its prominent and highly active megathrust where three plates—the Australian, Eurasian, and Indian Ocean plates—overlap and whose rupture had produced the quake and monstrous wave. Just last summer, Sieh had been farther south in Sumatra, installing Global Positioning System (GPS) instruments to measure local ground movements, and educating villagers about how to prepare for a major earthquake and tsunami, which he had warned could come in their lifetimes. To the locals, the geologist’s warnings now seemed prophetic.

On January 1, Sieh returned to Indonesia for six weeks to get a firsthand look at the geologic effects of the earthquake, to distribute relief supplies, and to check on the welfare of the many friends he has made over the years. He was also there to download data from the GPS instruments, to make necessary repairs to them, and to talk again to local people about preparations for future earthquakes and tsunamis.

Sieh and Galetzka spent the first half of their time south of the equator, where they had set up 14 GPS instruments in the two years prior to the earthquake. The instruments show that western Sumatra is converging on eastern Sumatra at a rate of about five centimeters a year, because of the movement of the Indian Ocean plate. Decades of strain built up by that action were relieved suddenly during the massive December 26 earthquake. Because the area that Sieh studies is 200 to 500 miles from the epicenter, few people living there felt the earthquake, and while the tsunami was frightening and caused minor damage, no one was killed.

The villagers warmly welcomed Sieh and his team back, and some said that they believed the GPS instruments had protected them from the devastation and death suffered by their countrymen to the north. Sieh tried to convince them that there was no connection between the instruments and their safety, while also warning them that the next massive earthquake in the region will likely be at their doorstep, where the convergence of plates continues to build up pressure.

On his recent trip to Sumatra, Caltech geologist Kerry Sieh traveled by helicopter to areas that he has been studying—regions that he predicts could face another massive earthquake and tsunami within the next 50 years.

Sieh took up studying the seismic history of Sumatra to better understand seismic activity in California. Up until a decade ago, he had focused much of his attention on the San Andreas Fault, discovering that its major earthquakes occur at irregular intervals of about 50 to 300 years, even though strains are building up regularly. He then set out to understand why. But paleoseismology—a field Sieh pioneered—along the San Andreas had become frustratingly time-consuming and was too imprecise to yield a satisfactory answer. In the late 1980s, the work of Gerald Wasserburg, Caltech’s MacArthur Professor of Geology and Geophysics, Emeritus, and his student, Larry Edwards, PhD ’88, inspired Sieh to look elsewhere—in the tropics, in fact. Sieh says that Wasserburg and Edwards had just begun to figure out how to determine very precisely the age of coral samples. Sieh figured that paleoseismic studies of coral reefs above the active Sumatran megathrust “would yield results faster and with more precise dates for ancient earthquakes.”

So, for the past decade, Sieh, Galetzka, and their colleagues have been collecting and analyzing corals to see if the big earthquakes occur on a regular basis over long timescales. “We’re also looking to see if there are unusual signals in both the coral and the GPS recordings that might presage the occurrence of a large earthquake,” Sieh says. “The paleoseismic work shows that sometimes giant earthquakes occur in couplets and sometimes singly, and that these singlets or couplets occur about every two centuries.”

Along that part of the Sumatran megathrust south of the equator, giant earthquakes that caused massive tsunamis last struck in 1797 and 1833. Mohamed Chlieh, a postdoc in Caltech’s Tectonics Observatory, has used Sieh’s data to calculate that the islands lurched more than 30 feet away from mainland Sumatra during the magnitude 8.7 earthquake of 1833. Sieh says that he is concerned that the December 26 quake may presage a similarly massive quake along the southern half of the Sumatran plate boundary, since the pressure there has been building since the couplet of 1797 and 1833 and may have been increased further by the latest shift. “We are telling residents of the region that it likely will happen in the lifetimes of their children,” says Sieh. “If they don’t prepare for this, they’re taking a big gamble.”

Sieh returned to Caltech in mid-February and did not have time to accompany Galetzka to Aceh Province. While in Banda Aceh, the provincial capital, Galetzka met with local officials and was directed to a small town called Lamno, about 25 miles to the south, where relief agencies had set up operations.

As with Banda Aceh, the approach to Lamno involved traveling up a river to get to the center of town. “The river was about 150 yards wide,” Galetzka says. “We passed a bridge that had been destroyed by the tsunami. All that remained were the concrete abutments. I could see that the tsunami had come up eight meters in some places and 18 meters in others. It flattened everything for two kilometers except one or two of the stronger structures.”

Local officials gave Galetzka and his colleagues permission to install a GPS station on a hill up from the damaged bridge. While they were installing it, a teenage boy came by to watch them work. “He was off at school in Banda Aceh at the time of the tsunami,” Galetzka says. “He had returned to Lamno and found that his home, family, and village were gone. This part of Lamno had been inhabited by at least 1,200 people. Only about 10 percent survived. I was amazed at the boy’s steady demeanor. He had probably cried so much that he couldn’t grieve anymore.”

Later that night, Galetzka and his colleagues presented a talk to several hundred people in Lamno. “They had a lot of questions about plate tectonics, and we cleared up misinformation and rumors. They didn’t need to know about how to survive a quake and tsunami, since they had already been through that.”

Galetzka and Sieh say that educating the public in Sumatra about earthquake and tsunami dangers is an important part of their work. “The educational component is really Kerry’s idea,” Galetzka says. “He believes that the science should serve mankind.”

Sieh and Galetzka plan to return to Sumatra in June to continue installing GPS stations and offering more educational seminars. Originally they had planned to install a total of 34 GPS stations in the region; now they are considering putting in significantly more. They and their colleagues are also working on a system that will allow data to be retrieved through satellite telemetry. “It’s possible that such a network of GPS stations could be the sensors for a tsunami early-warning system,” says Sieh.

Locals did seem better prepared, with many fleeing to higher ground immediately, after a magnitude 8.7 earthquake struck Indonesia March 28. Its epicenter was located just 110 miles southeast of the December 26 temblor, causing significant but localized destruction off the coast of north

Sumatra on the islands of Nias and Simeulue. Sieh says scientists will probe the relationship between the two quakes in the weeks ahead. “This certainly brings to the forefront the scientific question of one fault rupture triggering another.”

Before December 26, says Sieh, Sumatran officials could reasonably say that they didn’t have the funds to prepare for a massive earthquake and tsunami. “Now they have the interest and perhaps they will have the money,” Sieh says. “Three hundred thousand people lost their lives. Let’s hope they didn’t lose their lives for nothing.”