Reducing the Risk
In 1977 Congress passed the Earthquake Hazards Reduction Act, which put NSF in charge of a substantial part of earthquake mitigation research efforts in the United States. Earthquake-related studies, especially with regard to structural and geotechnical engineering, now make up the bulk of NSF's natural disasters research under the guidance of the National Hazards Reduction Program in the Directorate for Engineering. Why engineering? Because most of the immediate deaths from earthquakes occur when buildings collapse, and the huge economic losses associated with the biggest quakes stem from damage to the structures and infrastructures that make up cities and towns. In 1997, NSF officially charged three established earthquake centers with the responsibility of conducting and coordinating earthquake engineering research for the United States. The centers, each constituting a consortium of public and private institutions, are based at the University of California at Berkeley, the University of Illinois at Champaign-Urbana, and the State University of New York at Buffalo.
The NSF-funded earthquake centers are models of cooperation, including not only geoscientists and engineers but also economists, sociologists, political scientists, and contributors from a host of other disciplines. The Buffalo center, for example, recently studied the potential economic impact of an earthquake in the Memphis, Tennessee, area near the epicenter of several major quakes that struck in 1811-12. Participants in the study included researchers from the University of Delaware's Disaster Research Center, who examined economic, political, and social elements of the hazard. The Delaware researchers have also studied the impact that the Loma Prieta earthquake (1989) and Hurricane Andrew (1992) had on businesses in the Santa Cruz and Miami areas, respectively. Kathleen Tierney, a sociologist at the University of Delaware and a co-principal investigator for the Buffalo earthquake consortium, says the few previous studies of long-term disaster impacts focused on individuals and families rather than on businesses. The new Delaware research should help both policymakers and business owners better understand the economic impacts of disasters and devise more effective ways of coping with them.
While understanding the economic impact of disasters is important, the heart of the earthquake centers' mission is to design safer buildings. In 1967, the University of California at Berkeley center installed what is still the nation's largest "shake table." The twenty-foot-by-twenty-foot platform reproduces the seismic waves of various earthquakes, allowing engineers to test model structures. After the Loma Prieta quake, NSF funded an upgrade of the table from two- to three-dimensional wave motions; additional digital controls and sensors will soon allow offsite researchers to monitor experiments at the shake table in real time via a computer network.
Ultimately, says William Anderson, senior advisor in NSF's Division of Civil and Mechanical Systems, the research community may be able to conceptually link geophysical and geotechnical researchsuch as computer models of faults and soil liquefactionto the engineering simulations of building parts, creating a unified, integrated mathematical model of disaster.
The need for such research has been underscored numerous times in the latter part of the twentieth century. Early in the morning on January 17, 1994, southern California suddenly heaved and swayed. Deep beneath the town of Northridge, less than 25 miles from downtown Los Angeles, one giant chunk of the Earth's crust slipped over another, jolting the people and structures above with a 6.7 magnitude earthquake. (On the logarithmic Richter scale, 7.0 constitutes a major earthquake. Although the Richter scale has no upper limit, the largest known shocks have had magnitudes in the 8.8 to 8.9 range.) More than twelve thousand buildings were shaken so hard they collapsed or sustained serious damage, while many of the region's vital freeways and bridges disintegrated or were rendered impassable. Sixty people died and Californians suffered more than $25 billion in economic losses.
One year later and halfway around the world, the city of Kobe, Japan, endured its first catastrophic earthquake in a century, a 6.9 magnitude temblor. More than six thousand people died and almost two hundred thousand buildings were destroyed or damaged. Fires spread across the city while helpless firefighters failed to draw a drop of water from the shattered pipes. Besides the horrific loss of life, the devastation in Kobe cost between $100 and $200 billion.
The widespread destruction from these disasters has been especially alarming to experts because both cities sit atop a seismically active coastal region known as the Pacific Rim, which is capable of bestirring earthquakes of even greater violence. Close inspection of the rubble from both earthquake sites revealed one of the main contributing factors to the devastation: Buildings with steel frames exhibited cracks at the welded joints between columns and beams. Experts had expected old masonry and reinforced-concrete structures to crumble, but steel-framed buildings were supposed to be relatively safe. In Kobe, the steel frames failed catastrophically: more than one in eight simply collapsed. In Northridge, more than two-thirds of the multistory steel-framed buildings suffered damage.
Immediately after these disasters, NSF-sponsored researchers put new emphasis on developing better connection designs. In five short years, researchers have learned to reduce stresses on welds by altering the joints in the frames, in some cases by perforating or trimming the projecting rims (i.e., flanges) of the steel I-beams. These safer construction techniques have been included in new building code recommendations issued by the Federal Emergency Management Agency for all U.S. buildings in earthquake-prone regions.
NSF-funded researchers are finding many other ways to make buildings safer during earthquakes. Shih Chih Liu, program director in NSF's infrastructure and information systems program, says new high-performance concrete uses ash or small steel bars for better tensile strength and corrosion resistance. Other work is aimed at making the buildings themselves "smart." NSF-funded engineering professor Deborah Chung at the State University of New York at Buffalo recently invented a smart concrete that acts as a sensor capable of monitoring its own response to stress. The concrete contains short carbon fibers that lower the concrete's tendency to resist the flow of electricity (a quality that researchers call "resistivity"). Deformations to the materialas can occur during earthquakescause resistivity to rise, a change that can be gauged by a simple electrical contact with the concrete. The greater the signal, the greater the presumed damage. NSF-funded engineers have also developed systems such as swinging counterweights, which dampen the oscillations of buildings, and slippery foundations that are shaped like ball-bearings in a bowlthe bearings allow the structure's footings to shift sideways nearly independently of the structure above.
Other NSF-supported advances include the development of smart shock absorbers for buildings, bridges, and other structures. As the structure shakes or sways, electrical signals from motion sensors in the structure cause a special fluid in the shock absorbers to become thicker or thinner (ranging between the consistency of light oil to one more like pudding), depending on what's needed to slow or speed the movement of the shock absorbers' pistons.
In the new millennium, NSF plans to develop the Network for Earthquake Engineering Simulation (NEES)a kind of overarching cybersystem for earthquake engineering experimental research. Through NEES, researchers around the world can remotely access a complete system of laboratory and field experimentation facilities, of which there are currently more than thirty in the United States alone.