After Quake, Geology Research at Harvard Assumes New Urgency

Professors leading research initiatives in earthquake science at Harvard say there were prior indications of the earthquake that hit Japan two weeks ago, but that they were taken aback by its 9.0 magnitude.

“In terms of whether we should have earthquakes there, yes, we expect earthquakes,” said Miaki Ishii, an associate professor of Earth and Planetary Sciences. “In terms of whether we expected a magnitude 9.0 earthquake, I don’t think anyone expected it.”

A 7.2 magnitude earthquake two days prior to the earthquake alerted researchers to the possibility of a bigger earthquake event in the near future, according to Geophysics and Engineering Sciences Professor James R. Rice. But the Japanese have traditionally expected no larger than a magnitude 8.0 earthquake in the region.

“This is a fantastic learning experience,” Rice said, adding that the extensive network of seismic and GPS instruments across Japan allowed data collection about the earthquake of “unprecedented detail.”

The earthquake was caused by a collision between the Pacific and Eurasian tectonic plates, according to Adam M. Dziewonski, professor emeritus in the Department of Earth and Planetary Sciences, but its unexpected size was due to the large area over which these plates “slipped.”

Ishii used data collected from seismic stations across the United States to model the behavior of the earthquake’s wave fronts in video form.

“The exciting part of our result is that this earthquake could have been worse,” Ishii said, adding that the area of the region which slipped to cause the main shock of magnitude 9.0 was smaller than the total area involved in the earthquake event. “This earthquake could have been magnitude 9.4.”

The earthquake occurred over multiple rupture zones that have been involved in a number of previous Japanese earthquakes—but never all at once—according to Rice.

Rice’s colleagues Brendan J. Meade and Jack Loveless are studying how parts of the Earth move in relation to one another to better predict where earthquakes might occur in the future. Regions of the ocean floor that are “locked,” or not moving now, are potential sites for larger earthquake events.

“On a long term, the floor of the ocean is going to slip under Japan. If it’s not moving much now, it means that it’s got to catch up,” Rice said.

Understanding where earthquakes are most likely to occur can help scientists and engineers make more strategic decisions about infrastructure planning—and avoid the kind of dangers that the collapse of the Fukushima nuclear power plant has presented.

Professors agree, however, that most damage was caused by the subsequent tsunami that the earthquake caused.

Tsunamis form when earthquakes generate enough vertical motion to distort the ocean floor, pushing one side up and the other down. Water races forward to restore balance—it wants to stay flat—and the resulting wave is the tsunami, according to Rice.

But Dziewonski emphasized that the correlation between earthquakes and tsunamis is not straightforward. “[The] size of tsunami generated by earthquake depends on the way that the sea bottom breaks and that may not be directly proportional to the size of earthquake,” he said, adding that the depth of the earthquake dictates how much the ocean floor is deformed.

Rice said research at Harvard about tsunamis is relatively nascent but that geologic projects and understanding have made great strides and take on new relevance in light of the events in Japan.

“Harvard has a great commitment to earthquake science,” he said.

—Staff writer Radhika Jain can be reached at radhikajain@college.harvard.edu.