Engineering to a Fault

The United States Geological Survey estimates that several million earthquakes occur around the world every year. They are not always high in magnitude, however, they present unique problems and challenges to structures that engineers have to account for in their work. 

This week, geologists announced the discovery of a new fault line in San Francisco. Worryingly, the new fault zone intersects the Rodgers Creek and Hayward Faults, essentially connecting the two. David Ponce, a geologist at USGS, explained: “That’s a big deal. Because the longer a fault stretches, the bigger the magnitude of an earthquake it can produce. And here we’ve just doubled the length of this fault.

At the helm of the discovery was Janet Watt, who along with her team from the United States Geological Survey has published their findings in the journal Science Advances. Ponce warns that 2.4 million people could be directly affected when an earthquake occurs. There is also a huge engineering implication when the earthquake does happen. Ponce said: “It also turns out that major transportation, gas, water and electrical lines cross this fault. So when it goes, it’s going to be absolutely disastrous.” In their report, they indicate that deaths and billions of dollars in property damage would also be unavoidable if a magnitude 7.4 hits. The geologists estimate that there is a 32% chance of a magnitude 7.4 earthquake occurring in the next 30 years. 

So what can engineers do to lessen the effects that the inevitable earthquake will bring? Earlier this year, homeowners in California were told that they could get grants of up to $3,000 to retrofit single-family homes with materials that would render them earthquake-proof. Engineers pointed out that single-family homes built before 1979 were not bolted to their foundations. Therefore, in the event of an earthquake, the houses’ structural integrity could not be guaranteed. 1.2 million houses in California were purportedly in trouble of being unprepared for earthquakes, according to the LA Times.

Furthermore, engineers can race to install safety shut-off valves in key pipelines that are in danger of exploding or leaking once the earthquake hits. This would be beneficial for natural gas pipelines, for example. The particular valve that can be used is coincidentally named Koso - The California Valve. These valves are earthquake-sensitive gas shut-off valves. They shut off in the event of an earthquake and prevent gas flow into a structure where earthquake damage may have occurred. The only issue is that the industrial-sized valves cost $7,750.00 each. However, with the promise of billions of dollars of infrastructure damage, it may be a price the government should be willing to pay. Smaller versions of the valves are available to homeowners as well.

Engineers have also been experimenting with what is known to the industry as seismic invisibility cloaking. It involves drilling empty boreholes 5 meters deep and putting what is known as a metamaterial down into the hole which divides and reduces seismic waves’ effects. Engineers are hoping to implement this system to buildings, airports, power stations and dams to alter the amount of seismic pressure the facilities experience. Seismic waves get converted to evanescent waves that die down as they travel. However, this technology is still in an experimental phase.

What about key structures that humans rely on to navigate with during a disaster like an earthquake? You could find yourself on this structure during an earthquake, which in some cases, might prove fatal. Luckily, engineers build bridges to try and withstand earthquakes. Researchers at Purdue University, in 2014, published their designs for bridges that would see less damage during earthquakes. The new design included a “framework of columns and beams” that would support the bridge when an earthquake hit. They call them ‘bents’. These are pre-fabricated off-site, transported to the construction site and then installed onto a bridge. This allegedly hastens up the construction of the bridge and ensures it can be done in a timely manner. 

John Stanton, a professor in the Department of Civil and Environmental Engineering at the University of Washington said: “The design of reinforced concrete bridges in seismic regions has changed little since the mid-1970s. However, pre-fabricating means the pieces need to be connected on-site, and therein lies a major difficulty. It is hard enough to design connections that can survive earthquake shaking or to design them so that they can be easily assembled, but to do both at once is a real challenge.” 

In Vancouver, Canada, the city has just undergone their annual Shakeout earthquake drill, observed on the 20th of October every year. This year, the city celebrated a new network of seismic sensors being installed on the ocean floor. They are engineered to sit on the ocean floor and will give a 90-second warning to seismologists once an earthquake is detected. It detects the “primary wave of energy” than an earthquake generates. The primary wave is a precursor to the secondary wave which is the actual wave that causes a shaking effect on land. The primary wave will give the city a 90-second warning that an earthquake is imminent. Canada is also expecting a large earthquake in the next 50 years due to being on the Cascadia fault.