Posts Tagged ‘seismology’
“One person’s data is another person’s noise”*…
A drop in seismic noise from humans could help scientists track volcanic tremors in places like Auckland, New Zealand. Credit: Wikipedia/DXR, CC BY-SA 3.0
Seismic noise has dropped by half during coronavirus lockdown measures, giving scientists a rare lull to search for hidden signals usually drowned out by human activities.
Researchers measure seismic waves coming from natural sources, like earthquakes and volcanoes, as well as human activities. Trucks, cars, factories, and even shopping can create high-frequency seismic waves radiating out from population centers, and most scientists filter out human noise to seek for natural signals.
But seismic noise has been unusually quiet lately, in what scientists are calling the “anthropause.”
“If it’s quieter now and we can pick up some of the smaller signals, that improves our seismic risk analyses,” said Paula Koelemeijer, a lead author on a study published today in the journal Science.
Tracking smaller earthquakes can help scientists understand larger, more dangerous quakes and monitor how faults move. When a magnitude 5.0 earthquake struck Petatlán, Mexico, on 4 July, a station 380 kilometers away was able to detect the quake from raw data. Normally, the station would have missed the small quake without filtering out noise.
“This is likely to become a landmark article in the fields of seismic monitoring and ambient noise tomography,” said volcanologist Jan Lindsay at the University of Auckland who was not involved in the study. “The ‘2020 seismic noise quiet period’ will likely become something that Earth science students of the future will learn about in textbooks.”
Globally, seismic noise dropped by a median average of 50% during the coronavirus lockdowns from March through May. The measurement includes all seismic signals, but scientists attribute the drop to human activity by comparing changes in seismic noise with mobility data from Google and Apple.
The drop in noise varied by location: It decreased by 33% in Brussels, Belgium; 50% in Sri Lanka; and 10% in Central Park, New York. Rural areas grew quieter too—noise at a station at Rundu, Namibia, dropped by over 25%. (Koelemeijer attributed the drop to fewer tourists at a popular hippo-watching spot nearby.) The study pulled data from 185 seismic stations across the globe in both urban and rural locales…
“This study impressively demonstrates just how much man-made noise there actually is,” said research associate Carolin Böse at the GFZ German Research Centre for Geosciences who was not involved in the research. “Seismologists around the world now have a chance to make good use of the data presented in this study and hunt for otherwise ‘hidden signals’ in the seismic recordings.”…
Taking advantage of the “anthropause,” scientists are listening for faint natural signals during the quiet of coronavirus lockdowns: “The Seismic Hush of the Coronavirus.”
###
As we celebrate (relative) silence, we might recall that one of the primary man-made sources of seismic “sound” got a boost on this date in 1870: America’s first asphalt pavement was laid in front of City Hall in Newark, N.J. Edmund J. DeSmedt, the Belgian chemist who oversaw the work, had received a U.S. patent for this asphalt paving method two months earlier. Later that year, DeSmedt became the inspector of asphalt and cements for the District of Columbia, and oversaw wide application there.
DeSmedt’s crews at work in D.C. in 1876
“I feel the earth move under my feet”*…
For more than a century, the San Andreas Fault has been considered the undisputed heavyweight champion of large-scale deformation in the West. It is here that the North American and Pacific Plates meet, jostling for position with often violent results. Eventually, the theory goes, the thin sliver of land between the fault and the ocean—from the southern tip of the Baja Peninsula to the Santa Cruz Mountains—will break off from the mainland and slide north, until LA drifts past San Francisco. But there’s at least one problem with this scenario: The San Andreas appears to have gotten jammed. Northwest of LA, near the town of Frazier Park, the fault is kinked out of alignment so dramatically that many geologists suspect the pent-up tectonic strain will have to seek release somewhere else…
[Nevada state geologist James] Faulds thinks he’s found the spot. It’s an emerging zone of instability, known as the Walker Lane, that closely follows Route 395. He believes that, over the next 8 million to 10 million years, the North American continent will unzip along this stretch of land, east of the San Andreas. The Gulf of California, which separates the Baja Peninsula from Mexico, will surge north into Nevada, turning thousands of square miles of dry land into ocean floor. (Mapmakers, if they still exist, may label the new body of water the Reno Sea.) While this geologic realignment will take long enough for human civilization to fall, rise, and fall again hundreds of times over, Faulds’ hypothesis is more than an academic curiosity. It represents a radical shift in how geologists use up-to-the-minute tools—satellite data, aerial surveys, computer simulations—to fathom age-old processes. And for residents of the West, it is an invitation to think in an altogether new way about the familiar-seeming ground beneath them. Now is the time: Already the Walker Lane region, with its booming population and burgeoning tech economy, is beginning to feel the rumblings of a new seismic regime…
The next Big One? “Move Over, San Andreas: There’s an Ominous New Fault in Town.”
* James Taylor and Carole King
###
As we ruminate on the rumbling, we might spare a thought for Richard Dixon Oldham; he died on this date in 1936. A geologist and pioneering seismologist, he made the first clear identification of the separate arrivals of P-waves (primary waves), S-waves (secondary waves), and surface waves on seismograms. Later, he developed the first clear evidence that the Earth has a central liquid core.
“The safest place to be during an earthquake would be in a stationary store”*…
The United States is currently gripped in a bout of earthquake mania, following a series of significant tremors in the West. And any time Yellowstone, LA, or San Francisco shakes, people start to wonder if it’s a sign of The Big One™ to come. Yet even after decades of research, earthquake prediction remains notoriously hard, and not every building in quake-prone areas has an earthquake-resistant design. What if, instead of quaking in our boots, we could stop quakes in their tracks?
Theoretically, it’s not a crazy idea. Earthquakes propagate in waves, and if noise-canceling headphones have taught us anything, it’s that waves can be absorbed, reflected, or canceled out. Today, a paper published in Physical Review Letters suggests how that might be done. It’s the result of French research into the use of metamaterials—broadly, materials with properties not found in nature—to modify seismic waves, like a seismic cloaking device…
Read all about it in “How a ‘Seismic Cloak’ Could Slow Down an Earthquake.”
* George Carlin
###
As we think soothing thoughts of stability, we might send scientific birthday greetings to Vincenzo Viviani; he was born n this date in 1622. A mathematician and engineer, Viviani is probably best remembered as a discipline of Galileo: he served as the (then-blind) Galileo’s secretary until his death; he edited the first edition of Galileo’s collected works; and he worked tirelessly to have his master’s memory rehabilitated. But Viviani was an accomplished scientist in his own right: he published a number of books on mathematical and scientific subjects, and was a founding member of the Accademia del Cimento, one of the first important scientific societies, predating England’s Royal Society.
You must be logged in to post a comment.