Seismic Mystery : Researchers Zero In on Epicenter

With only a flashlight and the shine from a half moon, Gerry Simila and Luis Munguia Orozco lugged several hundred pounds of seismic equipment late Sunday night along a narrow trail waist-high with tropical grass near this coastal Mexican town.

The sweating scientists were in a race against time to install delicate measuring devices to track the aftershocks of the earthquake that devastated a large part of central Mexico City last Thursday.

Toward the end of a grueling 17-hour day, driving through rugged mountain terrain, the binational scientific team had reached the suspected epicenter of the quake, a strangely serene coastal plain of coconut plantations and occasional tourist resorts.

The area’s lush beauty only added to the special mystery of Thursday’s quake for researchers: Why did it cause such destruction in Mexico City, 200 miles northeast, when previous coastal temblors had substantially fewer effects?

Important for Research

“This is an especially important quake to study for the future in both Mexico and California because the results seem difficult to explain,” said Karen McNally, director of the Charles Richter Seismological Laboratory at UC Santa Cruz and a specialist on Mexican earthquakes.

McNally was so determined to place her equipment within the epicenter region as soon as possible that she is spending $5,000 of her personal savings--and $5,000 wheedled from a special UC Santa Cruz account--ahead of confirmation for a funding commitment from the U.S. Geological Survey.

“Large quakes have no respect for a professor’s schedule or Oct. 1 fiscal year deadlines,” McNally said early Monday as she and Simila hunched over the first results of aftershocks etched on a drum recorder, a device in which a needle traces ground movement over a blackened cylinder.

Simila, a professor at Cal State Northridge, had canceled a research trip to New Zealand to rush to Mexico.

A Ton of Equipment

McNally’s team of 10 professors and graduate students joined Munguia’s 20-member group from Mexico’s National Center for Scientific Research and Education in Ensenada. Together, they mobilized to carry into Mexico within a day of the quake more than a ton of specialized equipment valued upwards of $100,000.

They then surmounted problems of obtaining electrical supplies, difficult drives over long distances and an initial inability to communicate by telephone between subteams.

Because McNally analyzes the sources of such quakes, data from the first 10 days to two weeks after a major temblor is critical to her research.

“The chance to study a large quake is so hit-and-miss that you must get in early,” she said. “In addition, there seems to have been so much energy released by this one that it may have been a so-called ‘complex event,’ two quakes on top of each other with shock waves coming one after another, far more damaging than a quake sending out a single wave.”

Felt at a Distance

Pantomiming a seismic wave with her hands as she careened a car around a mountain curve, McNally said that the quake, “instead of going bloop, might have gone bloop, bloop, bloop. “ Such a series of waves, because of their longer amplitudes, could affect distant locations built on soft soils, such as those of Mexico City, where poorly constructed buildings would “tune in” to the waves and sway in time.

The quake’s effects could also heighten the more-than-friendly competition among seismologists over which group would be first with explanations of unusual phenomena.

McNally and the research scientists in Ensenada were aware of plans by their counterparts from UC San Diego and the National Autonomous University of Mexico to collect information within the quake zone. UCSD and the Mexican university scientists had in place some instruments southeast of the epicenter, toward Acapulco, in expectation of activity, and whatever data is collected will eventually be shared, as will information from UC Santa Cruz recorders.

Cooperation, Competition

“We cooperate, but we do compete,” admitted McNally, adding that a limited amount of government funding for seismic research in both the United States and Mexico heightens rivalries.

For several years, scientists had expected a major quake along the coastal area here, since it sits atop an extensive seismic zone that appeared too quiet for too long--more than a century. McNally said she could not conceal her excitement when she was alerted about the temblor early last Thursday by the National Earthquake Information Center in Golden, Colo.

McNally was clearly disappointed when, after predicting a substantial aftershock, she found herself still on an airplane to Mexico when it occurred Friday evening.

However, McNally declared herself satisfied after the first equipment had been placed by Sunday to catch subsequent aftershocks, which she predicts will last for weeks, if not months.

But, contradicting the image of scientists eager for disaster, McNally said, “It’s much worse to predict no quake in cases like this than to predict a quake that doesn’t happen. Aftershocks are also going to help us understand how these things happen so we can avoid as great a problem the next time.”

As she did Tuesday morning, McNally will continue during the next week to pore over data from 35 portable measuring stations, repositioning them daily throughout the coastal region to monitor areas of strongest activity.

She hopes the information eventually will reveal patterns useful to spot specific potential seismic disasters both along Mexico’s Pacific coast and within California.

“We want our guesses to get better and better,” McNally said.