Two stone discs and a flywheel may sound like a Flintstonian vehicle, but in fact, it’s the recipe for a new, rather high-tech device that scientists are using to study earthquakes in the lab, described in a recent Science paper.
Metamaterials—materials engineered to have optical, thermal, or other specific properties naturally occurring substances don’t—can block, bend, and otherwise manipulate all sorts of waves: they can, at least in theory, twist light to render objects invisible, contort ultrasound waves to hide things from sonar, and disguise the telltale wake of a submarine. Now, in an arXiv paper, Australian and Korean researchers have suggested another wave-altering use for metamaterials: protecting buildings from earthquakes’ powerful seismic waves.
A tower for removing gas at the Marcellus Shale Formation in Pennsylvania.
When it was revealed in November that several small earthquakes in northwestern England had been caused by fracking, the controversial process of extracting shale gas from bedrock by cracking the rock with pressurized water, the gas company responsible stated that it was an extremely unlikely occurrence. True as that may be, residents of Youngstown, Ohio, can now testify that something similar has happened again. This time, it wasn’t the removal of shale gas that triggered the earthquakes, but apparently the subsequent cracking of sandstone in order to store the wastewater produced by fracking.
Satellite radar data showed two wave fronts combining into a doubly tall tsunami off the coast of Japan on March 11.
The tsunami that spawned by the 9.0 earthquake off Japan this March was a disaster of massive proportions, reaching heights of over 130 feet in some areas and traveling up to six miles inland in others. Scientists at NASA and Ohio State University have now found another factor, beyond the sheer strength of the quake, that made the tsunami so ferocious: It started out as two separate walls of waves that combined to form one taller, more powerful “merging tsunami.”
One cable holds the bridge up.
San Francisco has its share of massive earthquakes, but the Bay Bridge, one of the city’s main transit arteries, is not as quake-safe as you’d hope. That’s why, alongside it, the state is building a massive new replacement structure—the largest self-supporting suspension bridge ever built. Jim Giles at New Scientist went to visit the bridge and provides a primer on its engineering:
In a regular suspension bridge, the cables that support the roadway are hung between two or more towers, like a hammock between trees, and anchored at each end by a connection to land. The new bridge is more like a sling. A single cable loops under the roadway, over the tower and beneath the roadway on the other side of the tower. The enormous forces placed on the cable by the road cancel out, leaving a structure that is balanced but not directly supported by a land anchor…
As the [road] segment fell into place it revealed the full length of tower that stands behind it, an elegant structure made up of four concrete pillars. These drop into enormous steel foundations, parts of which were built in Texas and shipped to California via the Panama canal. The pillars are connected by “shear beams”—relatively weak steel components that are designed to break if the towers move. The two roadways, one each for east and westbound traffic, hang from the cables but are not attached directly to the tower. This arrangement means that the four pillars and two roadways will sway when a quake hits, but remain intact even through the strongest shaking that geologists expect the region to experience over the next 1500 years.
Read more at New Scientist.
Image courtesy of Bay Bridge Information Office.
The magnitude 5.8 quake that struck central Virginia on Tuesday was felt from Florida to Maine to Missouri. “This is probably the most widely felt quake in American history, even though it was less than a 6.0,” says Michael Blanpied, a USGS seismologist DISCOVER contacted after the event. The reason for this intensity is that the East Coast, like the controversial New Madrid Seismic Zone in the central U.S., is located amidst old faults and cold rocks in the middle of the North American tectonic plate, and seismic waves travel disturbingly far in such stiff, cold rock.
We would do well to take a hint from Tuesday’s expansive shake-up. It’s lucky that it struck in rural America. But a similar tremblor in the crowded cities of the central U.S. above the New Madrid zone is a matter of when, not if. And the region is woefully unprepared to mitigate the damage, as Amy Barth explores in a piece from an upcoming issue of DISCOVER:
The disastrous winter of 1811–12 is the stuff of legend in the Midwest. In the span of a few months, three major earthquakes rocked Missouri, Tennessee, and Arkansas, violently shaking 230,000 square miles stretching from St. Louis to Memphis. Witnesses claimed that the ground rolled in waves several feet high and the Mississippi River flowed backward. Some reports described buckling sidewalks in Charleston, South Carolina, and tremors that reached as far as Quebec. Had seismographs been available at the time, scientists believe those tremors would have registered magnitudes at least as great as the 7.0 quake that devastated Haiti in 2010 and possibly as high as 8.0. These would place them among the worst in U.S. history.
What’s the News: The tsunami that deluged Japan in March was so strong that it broke off several large icebergs in Antarctica, 8,000 miles away, researchers report in a new paper [pdf]. Using satellite images, the researchers saw the tsunami causing new icebergs to split off—or calve—from an ice shelf, the first time such an event has been observed.
The National Palace in Port-au-Prince
after the 2010 Haiti earthquake
What’s the News: To dampen structural vibrations from earthquakes, engineers often place a flexible layer of rubber bearings in between buildings and the soil. Now, scientists are learning that Mother Nature uses a similar technique. A research team has found that a buried layer of mangrove in the Caribbean island of Guadeloupe absorbs earthquake energy, shielding the above ground from soil liquefaction. This discovery could be exploited to help protect new buildings in the Caribbean islands.
Destruction in L’Aquila, in the seismically active area of Abruzzi.
What’s the News: No one can predict earthquakes. But six seismologists and a government official are being tried for manslaughter in the deaths of more than 300 people in the 2009 tremblor in L’Aquila, Italy. The city’s public prosecutor says the scientists downplayed the possibility of a quake to an extent that townsfolk did not take precautions that could have saved their lives. A judge has just set the trial to begin on September 20.
In this images of infrared radiation in the days before the March 11 earthquake, the red circle indicates the epicenter and the red lines are tectonic faults.
What’s the News: Scientists analyzing the March 11 earthquake in Japan will have the benefit of some of the most sensitive and comprehensive atmospheric data yet, thanks to satellites monitoring climate. And a team has now reported a strange effect—a sudden spike in the temperature in the atmosphere above the quake site—detected just before the event. If the spike was related to the quake, and other earthquakes do the same thing, it might help scientists predict such cataclysms in the future.