Quake Queller: A New Technology Called the Seismic Muffler Brings New Hope for Reducing Earthquake Damage

By Russ Banham

Leader’s Edge

On Jan. 17, 1994, a 6.7-magnitude earthquake struck the San Fernando Valley region of Los Angeles, killing 72 people, injuring more than 10,000, and causing an estimated $40 billion in widespread property damage. Thousands of homes, buildings and cars were destroyed in what remains one of the costliest catastrophes in U.S. history.

The Northridge Earthquake, named for its apparent epicenter (later determined to be the nearby community of Reseda), stunned seismologists with its ferocity. Catastrophe prediction models had estimated the probability of a 6.7-magnitude earthquake as a one in 500-year event. Now, just 24 years after Northridge, scientists at the U.S. Geological Survey predict a 99.7% of another 6.7-magnitude temblor in Los Angeles within the next 30 years.

Much worse is the possibility of a mammoth earthquake striking coastal residents of the Pacific Northwest along the 620-mile Cascadia Subduction Zone, where the Juan de Fuca ocean plate dips under the North American continental plate. The fault zone encompasses the cities of Seattle and Portland, which confront an 8% to 20% chance of experiencing a magnitude-8.0 or higher quake in the next 50 years.

Such doom and gloom projections are daunting for anyone living along the western coastline of the United States. The risk is also of great economic consequence to the global insurance and reinsurance industries, which absorb the financial brunt of earthquakes along with local, state and federal taxpayers. The Northridge Earthquake alone caused insured losses estimated at $25.6 billion in 2017 dollars, more than the industry had collected in earthquake premiums over the prior 30 years. According to the Federal Emergency Management Agency, the damage losses add up to $4.4 billion annually nationwide. Across the planet, earthquake losses in 2016 alone surpassed $53 billion.

Limiting the Impact

On average, roughly 500,000 detectable earthquakes occur each year, of which 100,000 can be felt and 100 cause significant property damage. For millennia, people living in regions prone to earthquakes have tried to limit the impact of earthquakes on buildings. Pliny the Elder’s history of ancient Greece includes a reference to the use of sheepskin between the ground and the foundation of a temple to permit the structure to slip and slide with less damage during a temblor. This ancient prevention technique is actually a primitive version of base isolation, a current protection technology. In base isolation, spring-like flexible pads are inserted between a building’s foundation in the ground and the building itself to absorb devastating ground motions.

Now another earthquake protection technology has been developed to do something similar, albeit in a way that stretches the bounds of credulity. OK, it blows the mind.

Developed by scientists at the Massachusetts Institute of Technology’s Lincoln Laboratory, it’s called a seismic muffler, at least for the time being. The concept calls for drilling a V-shaped array of boreholes hundreds of feet deep that slope away from the protected asset, such as a building, an airport runway or a power plant. The array of boreholes one to three feet in diameter is similar in shape and dimension to a set of trench walls.

Cased in steel or a comparable composite material to maintain the structural integrity of the underlying soil and rock, the boreholes divert hazardous surface waves generated by an earthquake away from the protected asset. The bottom aperture of the borehole array allows only higher-frequency, lower-energy seismic waves traveling from the depths of the Earth to enter and propagate. By the time this wave energy reaches the ground surface, it dissipates in much the same way the sounds emanating from a car’s combustion engine are softened by an acoustic muffler.

Tabletop exercises by MIT’s Lincoln Lab, using 3-D supercomputing calculations, indicate the V-shaped array of mufflers can decrease the ground-shaking effects of a 7.0-magnitude earthquake to a 5.5-magnitude earthquake and lower. That’s a vast improvement, given the logarithmic Richter magnitude scale. For the purposes of simple math, a magnitude-7.0 quake is 10 times stronger than a magnitude-6.0 quake but is 100 times stronger than a magnitude-5.0 quake.

Will a seismic muffler work in practice as it does in the lab? The answer appears to be yes. A patent has been issued for the technology, and a 20-page scientific research paper on the muffler was peer reviewed and published in the November 2018 Bulletin of the Seismological Society of America. “We have already received licensing interest in the technology,” says Robert Haupt, the Lincoln Lab staff scientist leading the development of the new earthquake protection system.

Too Good to Be True?

“Wow” factor aside, the technology has yet to be tested in the field. However, the boreholes in their V-shaped array (see diagram) should perform as intended, diverting surface energy away from the protected asset. Questions certainly remain, including the effect of these reflected waves on neighboring structures, the impact of drilling thousands of boreholes, and the overall cost compared to existing technologies, such as base isolation, which is limited to new construction. The effectiveness of boreholes may be greater than base isolation, since the total surface wave energy is diverted. But more analysis, including cost analysis, would be needed to determine the relative effectiveness of each approach for a particular property.

Putting aside these answers for the moment, we sent a description of the new technology to several structural engineers, a leading catastrophe risk modeler, two state insurance regulators, two large reinsurers, and the California Earthquake Authority. Collectively, their interest was piqued, but they were guardedly optimistic. As Dave Jones, then California insurance commissioner (his term ended in 2018), puts it, “The question comes down to what is realistic and affordable. While this appears promising, will it prove to be practical and affordable?”

“I read the piece you sent with an open mind, and it seems perfectly plausible to me,” says Keith Porter, a research professor in the Department of Civil, Environmental and Architectural Engineering at the University of Colorado. “That’s not saying I would recommend its use tomorrow, because it is not quite there yet, much less available. But I get the concept. The fact that it is peer reviewed in such a reputable journal gives further credence to its scientific validity and usefulness.” Porter holds a PhD in structural engineering from Stanford University.

Certainly, there are obstacles in the way of deploying the technology, including the need to obtain site access permits to bore thousands of holes. But Haupt believes the benefits of the solution overshadow its impediments.

“As long as you’re able to drill the boreholes at a distance of 300 meters or so from the asset, you can protect all kinds of structures—from a nuclear power plant to an entire neighborhood of residential homes,” he says. “If a community like Beverly Hills wanted to invest in putting this in to protect their homes on an aggregate basis, the destructive ground motion from an earthquake would be significantly reduced.”

This possibility caught the attention of Janiele Maffei, chief mitigation officer at the California Earthquake Authority, a privately funded, publicly managed organization that sells California earthquake insurance policies through participating insurance companies. Maffei, a registered structural engineer, is responsible for directing the authority’s statewide residential earthquake retrofit program.

“That’s a very interesting possibility, since we’ve been looking solely at mitigation on a building-by-building basis,” Maffei says. “The possibility of protecting more than one structure at a time is an exciting thing, particularly in California, which bears two thirds of the nation’s earthquake risks.”

Maffei cautioned that her opinion is tempered by financial reality—that is, the cost of the new technology. Other experts agreed. “This all sounds very interesting and promising, but we need to consider the real-world implications of the technology, chiefly its scalability and cost-effectiveness,” says Erdem Karaca, Swiss Re’s head of catastrophe perils in the Americas. (Not incidentally, Karaca holds a PhD in civil engineering from MIT.) “We’re talking thousands of boreholes drilled hundreds of meters deep to protect a hospital or a power plant. Is this safe? And how much will it cost?”

Haupt says the number of boreholes and their dimensions depend on the application. “Say you wanted to protect a kilometer-long airport runway,” he says. “The depth of the boreholes would be approximately 50 meters, the diameter about one foot, and the number of boreholes around 5,000 on each side of the runway.”

He further estimates it would require about 5,000 boreholes to protect a hospital, about 10,000 for a nuclear power plant, 40,000 for a 10-kilometer-long oil and gas pipeline, and 50,000 to 200,000 for a residential community (depending, of course, on its size). That sure sounds like a lot of boreholes, but Haupt countered that drilling with modern technology is “relatively straightforward.”

But what about the cost of all that drilling, compared to the expense of base isolation? According to various estimates, it costs $2,000 to $3,000 to drill a one-foot-diameter well 300 feet into the ground. And that’s just one borehole. Nevertheless, Haupt maintains the aggregate cost of seismic mufflers is much less than comparable base isolation expenditures.

“To build a tall skyscraper today using base isolation costs tens of millions of dollars per building,” he explains. “Based on general calculations from our extensive 3-D supercomputer computations, we estimate we could protect many more buildings at the same cost. So, yes, it would be cost effective.”

A more rigorous cost-benefit analysis will be available following the lab’s field-testing, Haupt says, noting that the lab is looking to drum up a combination of government and private-sector funding to produce a more comprehensive systems analysis. If the test findings are consistent with previous experiments and current cost estimations, former California insurance commissioner Jones says, the technology “could add a new level of protection for Californians. Anything we can do to reduce the potential for loss of life or property from damaging earthquakes we would support.”

Questions on Efficacy

Not all experts are optimistic about the efficacy of the technology. Robert Muir-Wood, the chief research officer at catastrophe modeling firm RMS, who holds a PhD in Earth sciences from Cambridge University, is dubious on several fronts. “This is interesting, ingenious and certainly a novel idea, but my gut reaction is that it’s science fiction,” Muir-Wood says. “Earthquakes are rich in many frequencies of vibration, and this procedure by design cannot anticipate what these frequencies will be prior to an event. It may muffle some frequencies but not all of them. Consequently, I don’t think it will work.”

Apprised of the criticism, Haupt responds that Muir-Wood is correct about earthquake vibration frequencies, which he equated to the frequencies in a broadband spectrum.

“He’s right that an earthquake does not produce a single tone of vibration but many different tones at once,” Haupt says. “But he may be unaware that our system is a broadband defense. By having multiple boreholes surrounding the protected asset, the surface waves approaching the borehole system are reflected or diverted. Any energy coming from below the earth and into the aperture is dissipated, enabling an indifference to frequency. So there is no frequency dependence.”

Karaca, from Swiss Re, brought up another concern—whether or not the V-shaped array of seismic mufflers might divert the energy of an earthquake toward neighboring structures. “Since the technology is designed to deflect surface waves, which are the most damaging aspect of an earthquake, that energy has to go somewhere,” he says. “My question is: where?”

“That’s an excellent query,” Haupt says. “He’s right that the energy will be diverted. However, the array pattern is designed to promote seismic wave self-interference, diverting the destructive effects of the waves. In other words, we’ve designed it in such a way that neighboring structures would not experience anything greater than the ground shaking already produced by the earthquake.”

Now What?

All in all, the unique earthquake protection technology appears to present a viable alternative to base isolation, although Haupt prefers to call it a “supplement” to current mitigations. The next step, he says, “is to go outside.”

The lab is undoubtedly eager to undertake real-Earth scenario testing, which Haupt believes will confirm the findings of the detailed 3-D supercomputer models demonstrating the technology’s effectiveness. Physical tests to date have involved drilling boreholes into thick blocks of plastic topped with scaled-down structures. To approximate different earthquake magnitudes, the blocks were shaken and the effects measured by an accelerometer. “We’re confident that the supercomputer modeling is accurate, but to really prove this works, we need to scale up the testing and experiment with actual boreholes drilled in the earth at different depths, densities, and so on,” Haupt says.

Like all academic laboratories, budgets are tight when it comes to large-scale tests. Is this something the insurance and reinsurance industries might be interested in funding, given the potential for a long-term return in decreased damage losses?

Maffei, from the California Earthquake Authority, is sanguine about the possibility. “Any technology that would mitigate the impact of an earthquake deserves monetary means for further testing,” she says. “When base isolation was explored in the aftermath of the Northridge Earthquake, it was tested first on a single structure. The results were encouraging, guiding its use in additional buildings. Little by little, it has proven itself.”

Richard Quill, expert risk research analyst at Allianz, shares this perspective. “We insure some of the earthquake risks affecting nuclear power plants and large oil refineries,” says Quill, who analyzes and coordinates the large reinsurer’s response to natural catastrophes. “If this technology is proven to work, it would obviously reduce earthquake damage risks to these facilities. From an insurance perspective, it is all very interesting. We’ve invested in the past in new risk-mitigation technologies, including how to make automobiles safer. But we would need more evidence.”

Russ Banham is a Pulitzer-nominated financial journalist and best-selling author.

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