Scientists shake things up to limit earthquake destruction

Pat Abbott Discusses Earthquakes in San Diego and Italy

In a matter of seconds, dozens of people were dead. Over the next hours and days, hundreds more would suffer the same sad fate.

The 6.3 magnitude earthquake that struck L’Aquila, Italy on the morning of April 6 killed 297 people and injured more than 1,100. It is estimated 11,000 buildings were damaged in some capacity. The central Italian city was home to about 72,000 people and left more than 60,000 people homeless.

Staggering figures like that make you sit up and take notice, especially when you consider that San Diego County has a whopping 41 times more inhabitants than L’Aquilla. In an earlier SDNN story, we examined the reality of living in earthquake country, just 90 miles east of the southern tip of the San Andreas Fault. The article discussed acknowledging that a big earthquake was going to hit the region, and knowing how to be best prepared for the event and what’s to follow.
The next question to address is how San Diego is working to limit the kind of death and destruction that befalls other countries, when “The Big One” hits.
Geologist and author Pat Abbott, a professor emeritus at San Diego State University, said Italy is one of the most earthquake active countries in the world. In a tectonics sense, he said, Italy is essentially a piece of Africa that is being pushed and shoved into Europe.

“That ongoing push is still going on,” he said. “It’s like being squeezed in a vice.”
But, he also said, due to the Italy’s lack of modern building codes, devastating destruction is far more likely there than in other places, namely California.
“There are lots of old buildings built out of stone and held together by simple mortar [in Italy],” he said. “It’s just a bad, bad place for earthquakes, and there’s no way around it. There are lots of cultural heritage sites; the cost to retrofit those buildings would be overwhelming. It’s hard to think of a reasonable solution of how do you protect people and cultural heritage at the same time.”
Knowing that, the charge to help make the region’s buildings safer and more able to withstand large seismic events is the passion of the structural department at UC-San Diego’s Jacobs School of Engineering.
Thanks to funding from the National Science Foundation, the school was able to build the world’s first outdoor “shake table” in 1995 at the Englekirk Center for Structural Development. The table allows for scientists to test the impact of seismic activities on structures to determine how well they perform during earthquakes. At 25-by- 40-feet, it is also the largest shake table in the United States.
“The table has been quite busy actually,” said Dr. Benson Shing, one of the project’s lead researchers and a professor of structural engineering at UCSD. “We are using it continuously, testing different materials. Most recently, we are working with stone masonry and wood-framed houses with brick veneer.”
See related:
L.A. earthquake should have San Diego taking notice
Magnitude 4.7 quake rattles nerves near Los Angeles
Shing’s crew is currently building a brick and mortar structure to shake test this July. It is a follow-up from a test that was performed in March on a similar structure (see video). The structures are similar to much of the 1920s era masonry and brick buildings that still exist in the area.
Shing said that the team looks at older building to see how they perform and newer more modern structures to see how they perform. They determine if there’s a need to improve current building code to enhance the safety. If the tests bear out improvement, they have to communicate with committees responsible for code development and get the process going.
“As structures change as the [building] codes change, and codes change based on earthquakes,” said Shing, who has more than 20 years in the structural engineering field. “And those buildings that are conforming to the most recent code are obviously expected to perform much better due to advancements in technology and other developments.”

(Photo by Eric Yates)
The shake table is built on steel plates and is operated by a below-ground system of hydraulic actuators. The actuators are powered by oil banks that can accumulate pressure and generate as much as 5,000 pounds per square inch, a measurement of pressure. The pressure activates pistons which raise the table, and has an oil-based bearing that allows it to slide horizontally with little friction, which simulated earthquake-incident motions. Researchers can test structures weighing up to 2,200 tons and as tall as 100 feet. Its hydraulic actuators are capable of shaking at speeds up to 6 feet per second, allowing it to create simulations of the most devastating earthquakes ever recorded, even some as high as 8 or 9 on the Richter scale, according to Shing.
Shing said it takes a month-and-a half for construction of a new structure. After the structures are built, they must wait one month for curing and the mounting transducers (which can measure energy and transfer it to data gathering sources) to the specimen to measure the deformation and the acceleration that occurs during the shaking.
After the test, the team analyzes the data for several months and calibrates computer models for simulation to have a better understanding for the performance of the structures. They then extrapolate that data and use those models as a means to predict the performance of existing structures.
Abbott said you never really know how structurally sound a building will be until you actually have a quake.
“The earthquake will expose what was done right, and what was done wrong,” he said.
Hopefully, thanks to Shing and his extensive work, and for the potential lives at stake, when the Big One does eventually hit, a lot more will go right.

source: Eric Yates is SDNN deputy managing editor. E-mail: eric.yates(at)sdnn.com Read more: http://www.sdnn.com/sandiego/2009-06-05/news/environment/ucsd-scientists-shake-things-up-to-limit-earthquake-destruction##ixzz0Hawo1LQD&C