Over the past couple of decades, increasing seismic activity around the world has been identified as an impending threat to the strength and well-being of our bridges. Earthquakes have caused bridge collapses in the U.S., Japan, Taiwan, China, Chile, Turkey, and elsewhere. Therefore, we need to find ways to minimize seismic effects on bridges, both by improving existing bridges and refining specifications and construction materials for future bridges.

A large majority of bridges are made of steel and concrete. While this combination is convenient and economical, steel-concrete bridges don't hold up as well in strong earthquakes (7.0 magnitude or higher). Conventional reinforced columns rely on the steel and concrete to dissipate energy during strong earthquakes, potentially creating permanent deformation and damage in the column and making the column unusable.

Under earthquake loading, engineers allow for damage in column hinges to dissipate energy and prevent total bridge collapse. While that practice is widely accepted, the effects of hinge damage can interfere with disaster recovery operations and have a major economic impact on the community.

With funding from the National Science Foundation (NSF) and using NSF's George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES), civil engineer M. Saiid Saiidi of the University of Nevada, Reno (UNR), and his colleagues have discovered a solution. They've identified several smart materials as alternatives to steel and concrete in bridges.

Shape memory alloys (SMAs) are unique in their ability to endure heavy strain and still return to their original state, either through heating or superelasticity. SMAs demonstrate an ability to re-center bridge columns, which minimizes the permanent tilt columns can experience after an earthquake.

Nickel titanium, or nitinol, the shape memory alloy tested in the UNR project, has a unique ability even amongst SMAs. While the majority of SMAs are only temperature-sensitive, meaning that they require a heat source to return to their original shape, Nitinol is also superelastic. This means that it can absorb the stress imposed by an earthquake and return to its original shape, which makes nitinol a particularly advantageous alternative to steel. In fact, the superelasticity of nickel titanium is between 10 to 30 times the elasticity of normal metals like steel.

Many of us know nickel titanium from our flexible prescription eyeglass frames. The material allows frames to easily return to their original shape after being bent in any direction. Nickel titanium's uses are extremely varied, with applications that range from medicine to heat engines, lifting devices and even novelty toys—and now, earthquake engineering.

To assess the performance of nickel-titanium reinforced concrete bridges, the researchers analyzed three types of bridge columns: traditional steel and concrete, nickel titanium and concrete, and nickel titanium and engineered cementitious composites (ECC), which include cement, sand, water, fiber and chemicals. First, they modeled and tested the columns in OpenSEES, an earthquake simulation program developed at the University of California, Berkeley. Finally, they assembled and tested the columns on the UNR NEES shake table.

To strengthen the concrete and prevent immediate failure in an earthquake, the researchers used the shake tables to test glass and carbon fiber-reinforced polymer composites. Both composites substantially enhanced the reinforcing properties of concrete and the columns resisted strong earthquake forces with minor damage.

The results of both the modeling and shake table tests were extremely promising. The nickel titanium/ECC bridge columns outperformed the traditional steel and concrete bridge columns on all levels, limiting the amount of damage that the bridge would sustain under strong earthquakes.

While the initial cost of a typical bridge made of nickel titanium and ECC would be about 3 percent higher than the cost of a conventional bridge, the bridge's lifetime cost would decrease. Not only would the bridge require less repair, it would also be serviceable in the event of moderate and strong earthquakes. As a result, following a strong earthquake, the bridge would remain open to emergency vehicles and other traffic.

The number of earthquakes has increased dramatically over the past few years within the central and eastern United States. Nearly 450 earthquakes magnitude 3.0 and larger occurred in the four years from 2010-2013, over 100 per year on average, compared with an average rate of 20 earthquakes per year observed from 1970-2000.

This increase in earthquakes prompts two important questions: Are they natural, or man-made? And what should be done in the future as we address the causes and consequences of these events to reduce associated risks? USGS scientists have been analyzing the changes in the rate of earthquakes as well as the likely causes, and they have some answers.

USGS scientists have found that at some locations the increase in seismicity coincides with the injection of wastewater in deep disposal wells. Much of this wastewater is a byproduct of oil and gas production and is routinely disposed of by injection into wells specifically designed for this purpose.

U.S. Geological Survey geophysicist William Ellsworth reviewed the issue of injection-induced earthquakes in a July 2013 study published in the journal Science. The article focused on the injection of fluids into deep wells as a common practice for disposal of wastewater, and discusses recent events and key scientific challenges for assessing this hazard and moving forward to reduce associated risks.

Although it may seem like science fiction, man-made earthquakes have been a reality for decades. It has long been understood that earthquakes can be induced by impoundment of water in reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground formations.

Water that is salty or polluted by chemicals needs to be disposed of in a manner that prevents it from contaminating freshwater sources. Often, it is most economical to geologically sequester such wastewater by injecting it underground, deep below any aquifers that provide drinking water.

Wastewater can result from a variety of processes, including those related to energy production. For example, water is usually present in rock formations containing oil and gas and therefore will be co-produced during oil and gas production. Wastewater can also occur as flow back from hydraulic fracturing operations that involve injecting water under high pressure into a rock formation to stimulate the movement of oil and gas to a well for production.

Wastewater injection increases the underground pore pressure, which may, in effect, lubricate nearby faults thereby weakening them. If the pore pressure increases enough, the weakened fault will slip, releasing stored tectonic stress in the form of an earthquake. Even faults that have not moved in millions of years can be made to slip and cause an earthquake if conditions underground are appropriate.

Although the disposal process has the potential to trigger earthquakes, not every wastewater disposal well produces earthquakes. In fact, very few of the more than 30,000 wells designed for this purpose appear to cause earthquakes.

Many questions have been raised about whether hydraulic fracturing — commonly known as “fracking”— is responsible for the recent increase of earthquakes. USGS’s studies suggest that the actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes. While hydraulic fracturing works by making thousands of extremely small “microearthquakes,” they are, with just a few exceptions, too small to be felt; none have been large enough to cause structural damage. As noted previously, underground disposal of wastewater co-produced with oil and gas, enabled by hydraulic fracturing operations, has been linked to induced earthquakes.

USGS scientists are dedicated to gaining a better understanding of the geological conditions and industrial practices associated with induced earthquakes, and to determining how seismic risk can be managed.

One risk-management approach highlighted in Ellsworth’s article involves the setting of seismic activity thresholds for safe operation. Under this “traffic-light” system, if seismic activity exceeds preset thresholds, reductions in injection would be made. If seismicity continues or escalates, operations could be suspended.

The current regulatory framework for wastewater disposal wells was designed to protect drinking water sources from contamination and does not address earthquake safety. Ellsworth noted that one consequence is that both the quantity and timeliness of information on injection volumes and pressures reported to the regulatory agencies is far from ideal for managing earthquake risk from injection activities.

Thus, improvements in the collection and reporting of injection data to regulatory agencies would provide much-needed information on conditions potentially associated with induced seismicity. In particular, said Ellsworth, daily reporting of injection volumes, and peak and average injection pressures would be a step in the right direction, as would measurement of the pre-injection water pressure and tectonic stress.

There is a growing interest in understanding the risks associated with injection-induced earthquakes, especially in the areas of the country where, before the modern boom in oil and gas production, earthquakes large enough to be felt were rare.

For example, wastewater disposal appears to be related to the magnitude-5.6 earthquake that struck rural central Oklahoma in 2011 leading to a few injuries and damage to more than a dozen homes. Damage from an earthquake of this magnitude would be much worse if it were to happen in a more densely populated area.

The USGS and Oklahoma Geological Survey (OGS) have conducted research quantifying the changes in earthquake rate in the Oklahoma City region, assessing and evaluating possible links between these earthquakes and wastewater disposal related to oil and gas production activities in the region. In a joint statement {http://www.usgs.gov/newsroom/article.asp?ID=3710}, USGS and OGS identified wastewater injection as a contributing factor for the 2011 earthquake swarm and damaging magnitude 5.6 event.

Studies show one to three magnitude 3.0 earthquakes or larger occurred yearly from 1975 to 2008, while the average grew to around 40 earthquakes per year from 2009 to mid-2013.

“We’ve statistically analyzed the recent earthquake rate changes and found that they do not seem to be due to typical, random fluctuations in natural seismicity rates,” said Bill Leith, USGS seismologist. “These analyses require significant changes in both the background rate of events and earthquake triggering properties needed to have occurred to be consistent with the observed increases in seismicity. This is in contrast to what is typically found when modeling natural earthquake swarms.”

The Oklahoma analysis suggests that a contributing factor to the increase in earthquakes occurrence may be from injection-induced seismicity from activities such as wastewater disposal. The OGS has examined the behavior of the seismicity through the state assessing the optimal fault orientations and stresses within the region of increased seismicity, particularly the unusual behavior of the swarm just east of Oklahoma City.

As the use of injection for disposal of wastewater increases, the importance of knowing the associated risks also grows. To meet these challenges, the USGS hopes to increase research efforts to understand the causes and effects of injection-induced earthquakes.

More useful, at least for now, are earthquake early warning systems, such as the one in Japan. The Japanese system detects a quake just as it begins to shake and sends alerts to cellphones, televisions, schools, buildings and mass transit systems before destructive waves reach a population center. If the effectiveness of such a system is maximized, it would allow trains to stop, elevators to come to a halt and people to get to safety before the worst of the shaking.

The earthquake’s epicentre was 20km from Bhuj. A city with a population of 140,000 in 2001. The city is in the region known as the Kutch region. The effects of the earthquake were also felt on the north side of the Pakistan border, in Pakistan 18 people were killed.

The earthquake was caused at the convergent plate boundary between the Indian plate and the Eurasian plate boundary. These pushed together and caused the earthquake. However as Bhuj is in an intraplate zone, the earthquake was not expected, this is one of the reasons so many buildings were destroyed – because people did not build to earthquake resistant standards in an area earthquakes were not thought to occur. In addition the Gujarat earthquake is an excellent example of liquefaction, causing buildings to ‘sink’ into the ground which gains a consistency of a liquid due to the frequency of the earthquake.

What earthquakes do