2010 Easter quake reveals much to the scientific world

Orlando Teran is a month away from publishing a peer-reviewed scientific article that could change the way development occurs along fault lines in California.

He has the 2010 Easter Sunday earthquake to thank for that discovery.

The five-year-old magnitude-7.2 earthquake centered in southeastern Mexicali Valley is known as the El Mayor-Cucapah Earthquake to the scientific community, named for a major fault system that runs through the Cucapah Mountains near Cerro Prieto.

The destructive quake caused untold millions of dollars of damage to the Mexicali area, injuring hundreds, killing two and displacing thousands of residents whose homes were felled and farms were made uninhabitable.

For scientists in the United States and Mexico, however, the April 4, 2010, quake was a revelation, credited with unlocking several secrets and proving numerous theories about what major earthquakes are capable of and how they behave.

Teams of geologists and geophysicists from Ensenada, Baja California, and Pasadena have made numerous discoveries that will not just aid in future development but that have already factored into a working earthquake early-warning system.

“Everything about this earthquake was new and different,” said Dr. Kenneth Hudnut, a geophysicist at the U.S. Geological Survey’s Earthquake Science Center in Pasadena. He was among the principal investigators in analyzing the quake and publishing studies in its aftermath.

“This earthquake opened our eyes to earthquake behavior we have not seen before,” he said.

THE LATEST

A Ph.D. candidate in geology, Teran’s paper will be published in the journal Geosphere from the Geological Society of America.

In it, he said, details will reveal California building codes need updating, especially along the San Andreas Fault, which runs partially through northern Imperial County all the way to the San Francisco area.

“This paper redefines the geological criteria for setback distances,” he said. “If your faults have certain orientations and certain characteristics, then your setback distance should be ‘x’ amount.”

Setbacks are the distances from which inhabited structures can be built along fault lines.

The Alquist-Priolo Earthquake Fault Zoning Act of 1972 was adopted by California lawmakers in response to the 1971 San Fernando quake, often called the Sylmar Earthquake. In it, building codes are enforced on the local and county levels that require minimums of 50-foot setbacks in some cases.

With the San Andreas Fault, as with the faults that made up the El Mayor-Cucapah quake, setbacks of at least 700 feet would be recommended in some places where a combination or fault orientation and subsurface materials could cause liquefaction — the complete undermining of the ground through the displacement of earth and water — over a previously unheard of distance.

Teran is well-versed in what this earthquake can do, as he has also been a supporting author on many of the same publications as Hudnut. At the time of the quake — April 4 is Teran’s birthday, by the way — he was an intern under respected geologist Dr. John Fletcher of Ensenada’s Centro de Investigación Científica y de Educación Superior de Ensenada, or CICESE.

Teran and Fletcher were responsible for much of the data collection south of the border as USGS scientists assisted and worked north of the border in the hours after the quake struck.

Now working in Houston in the private sector, Teran said he doesn’t know how his article will be used in the revision of existing policy. If anything, he hopes it will draw attention to the need for increased geological scrutiny by state officials.

“It’s just a matter of the right person being convinced that (the setback distances) really do need to be redefined,” he said.

UNPRECEDENTED TAKEAWAYS

Before the El Mayor-Cucapah Earthquake, scientists already knew the basics of how a quake unfolds along single faults and in chain reactions along a complex system of faults.

What they didn’t know was over what distances some of those chain reactions could occur, distances that ended up defining how widespread damage could be and how severe.

Hudnut said previously it was believed that the farthest a quake could jump from one fault to another was 5 kilometers, or 3.1 miles.

The El Mayor-Cucapah quake showed that distance was doubled. Teran said the initial fault rupture occurred on the Pescadores Fault in the southern end of the Cucapahs, then jumped 10 kilometers, or 6.2 miles, to the Borrego Fault in the northern half of the Cucapahs.

Hudnut said geologists now believe there is the potential for quakes to jump faults at distances as far as 15 kilometers, or nearly 10 miles.

“That was the biggest fault rupture jump we had ever seen worldwide,” he said.

“The earthquake ended up breaking a big, long complicated fault system that went all the way from the north tip of the Gulf of California, all the way north of the U.S.-Mexico border, into the Yuha Desert,” Hudnut added.

The total length of the rupture, he estimates, was 120 kilometers, or nearly 75 miles. “An amazingly complicated rupture,” he said enthusiastically.

What the quake also taught scientists is how to define a major seismic event as a cascade of smaller sub-events making up the whole earthquake, Hudnut said.

These had been theories that some geophysicists already had, but the quake provided the much-needed data to prove those theories, in part because the sensors in place in Mexico from CICESE and in California from USGS help paint a precise picture.

In the coming years, this data would prove to be the missing piece of the puzzle to developing California’s earthquake early-warning system.

SHAKING UP WARNING SYSTEM

An earthquake early-warning system has been in development in California for some time. In fact, Hudnut said it is already working.

The El Mayor-Cucapah Earthquake played a big role in further perfecting its efficacy, helping to complete the modeling necessary to predict the path and scope of a major earthquake.

The April 4, 2010, quake was used along with the information and analyses of the 1992 magnitude-7.3 Landers quake near Yucca Valley and the 1999 7.1 Hector Mine quake in the Mojave Desert to build the model, Hudnut said.

He added a lack of funding, however, has delayed the release of the system for public use. It is working, he reiterated, but there need to be more sensors placed throughout the state to make it work to its potential and more of the data telemetry equipment necessary to relay information.

“The system has been developed to a high level of sophistication, but it needs more work,” Hudnut said.

A CHANGED EARTH (LESSER DISCOVERIES)

The El Mayor-Cucapah Earthquake brought with it some major — and not-so-major — changes to the topography of the Mexicali and Imperial valleys.

Scientists don’t seem to really count the deep crevices and buckled roads brought on by liquefaction as significant geological changes; rather, they look for undiscovered faults, changes in elevation and orientation, and previously unseen subterranean secrets.

North of the border, the quake unloosed a new fault, called the Yuha Fault, which split a section of Highway 98 and moved more than 2 inches, “a pretty healthy amount of trigger slip,” geologist Jerry Treiman said in 2010.

Hudnut said a portion of the U.S.-Mexico border fence near Mount Signal was warped. He explained a two-mile stretch of earth along the northern face of the mountain shifted a foot and a half, almost unnoticeable.

In Mexico, there was much sadness over the dozens of gashes in the earth that made family farms worked for generations unlivable.

Teran said the Mexican government relocated families from their land after those gashes pushed up water and sand from below the surface. In aerial photos taken by CICESE after the quake, lush green farm fields are pockmarked by light brown scars along the surface.

Although scientists count knowledge and understanding as important results of the El Mayor-Cucapah Earthquake, Teran said some financial good could come as a result.

The quake unearthed what is likely a new geothermal bed west of the Cerro Prieto Geothermal Power Station.

As of December 2014, aerial shots of the fault lines in the Cucapah Mountains show a steam geyser still rising above the earth.

“It means there is hot, pressurized water there,” Teran said. “I think they are planning to figure out a way to get energy out of it.”

Figuring things out has always been Teran’s goal — the goal of all of the scientists who contributed to his upcoming paper.

“My passion about studying this earthquake is studying what earthquakes can do,” he said, “to help not just the scientific community, but everyone.”

Top photo is courtesy of Dr. John Fletcher and Orlando Teran.

Bottom photo is courtesy of Jill Deen.

This article originally appeared in the Imperial Valley Press, April 5, 2015.