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Vol.26, No. 19 Apr. 9, 2001

Lamont Scientists Study India Earthquake Up Close

By Pamela Vu

Earlier this year, in a mere 15 to 20 seconds, a fault in the Indian state of Gujarat had completed its rupture and generated a magnitude 7.6 earthquake that became the second major earthquake to hit the region in the past 200 years, killing more than 18,000 people, injuring about 167,000, destroying 332,000 houses and causing nearly $1.3 billion in property damage.

The Jan. 26 earthquake led geologists to believe that the continental region is far more seismically active than previously thought. Researchers at Columbia’s Lamont-Doherty Earth Observatory have suggested that the event may be due to the formation of a new mountain range.

For Leonardo Seeber, research scientist at Lamont-Doherty, and five other geologists, the quake was not only a tragic piece of news from overseas, but also an important opportunity to learn about a major earthquake up close to help diminish the destruction from the next one.

Seeber and his colleagues have found geologic evidence of little plate tectonic movement in the area—consistent with Gujarat being situated away from the plate boundary. However, the increase in earthquakes and seismicity over the past two centuries may hint at the possibility of a new fault in the region.

“If sustained, this rate of seismicity would build high topography over a short geologic time,” said Seeber. “One astonishing possibility is the earliest indications of the development of a new mountain range. Another less astonishing option is that the historic seismicity is a relatively short burst that will be followed by a long quiescence.”

Seeber and his team equipped, with little more than backpacks, hiking boots, measuring tape and hand-held instruments, arrived in India a week after the earthquake. Their mission: to find and map the surface rupture and other geological effects of the earthquake.

“The Earth is a tectonically active planet,” said Seeber. “We plan to compare deformation caused by the earthquake with geologic structure accumulated as a result of millions of years of activity. We want to understand how the Indian earthquake relates to this geological evolution.”

The team started in Bombay and drove north along the west coast to Ahmedabad, the capital of Gujarat.

“Although Ahmedabad is 150 km, or 93 miles, from the epicenter, it suffered building collapses and casualties. In the epicentral area, however, entire towns were reduced to heaps of debris. Many essential infrastructures, such as bridges, dams and electrical distribution stations, were severely damaged. It was especially heart-wrenching to see the destruction of an already highly stressed environment,” said Seeber.

The fact that the quake occurred on India’s Republic Day(a national holiday(accounts for the high death count, especially in the cities where people were at home for the holiday.

Not only were modern structures damaged, but also archaeological treasures, including remains of the Indus Valley civilization that date back to the second millennium B.C.

After spending a day in Ahmedabad, Seeber’s team traversed the Indian hillside on foot in search of the ruptured fault and the geological lessons that can be drawn from the earthquake.

They located a fault rupture through the small town of Manfara, about 50 miles east of Bhuj, the commercial hub of Gujarat.

“We were able to find the fault by asking local inhabitants if they were aware of ground deformations,” he said. “We mapped the fault for 8 km, or 5 miles, and found up to 32 cm of right-lateral slip.”

Processes deep inside the Earth cause rigid plates at the surface to move in different directions. Most of the deformation is along plate boundaries where elastic strain builds up until the boundary-a fault-snaps in an earthquake. In such an event, some shear motion is accommodated across the fault, which can be several meters wide in the case of a large earthquake. The vibrations originating from this sudden shift cause buildings to fall, water to come out of the ground and landslides.

Los Angeles, Tokyo, Istanbul and northern India are located at the boundaries of large plates. Most earthquakes occur at plate boundaries, but some in the interior of plates, like the 1993 earthquake in central India that killed about 10,000 people. Gujarat is close to the boundary between the Indian and Arabian plates, but not on it. Whether or not seismicity in Gujarat is related to plate-boundary processes is a critical issue for basic science and for earthquake hazard in that area.

Humans can also trigger earthquakes through various activities, including detonating atomic explosives underground, drilling oil wells, mining and creating artificial lakes.

“Seismicity in central India increased dramatically in the 1960s, right around the time many reservoirs were impounded,” noted Seeber. “Therefore, the data suggest that human actions account for a substantial portion of the current seismicity in central India.” Widespread water withdrawal by pumping might be a factor in the Gujarat earthquake.

The long-term geological implications of the 2001 Gujarat earthquake are still being discovered. In the meantime, Seeber and his team plan to share their conclusions concerning the potential for future earthquake disasters with government officials worldwide, a core mission of Lamont-Doherty.

“It is important that all large earthquake events receive the most detailed study, no matter where they are located,” said Lamont-Doherty Director Michael Purdy.

“Scientists at Lamont-Doherty are driven to understand the generation of stresses within the earth that are the root of the events, and the extremely complex processes that actually trigger the release of these stresses in the form of an earthquake. Believe it or not, the understanding of exactly what happened at Gujarat will help us understand and mitigate earthquake hazard here in the U.S. These types of studies have the long-term goal of defining hazard potential in ways that are useful to the local, state and federal agencies charged with mitigating the impact of these tragic events. Such studies are at the heart of an exciting new initiative within the Columbia Earth Institute that is focused upon the quantification of risk associated with wide range of natural and anthropogenic events.”

Seeber agreed that data must be shared freely in order for science to progress and to have a positive influence on society.