What Is Under Your Feet?

Inner Earth: Scientists Discover Mountains and Plains 370 Miles Beneath Earth’s Surface

At school, we are thought that Earth is divided into three layers, which are the cortex, the mantle and the nucleus, which in turn is divided into an internal and external nucleus.

by Janice Friedman

A basic and accurate scheme, but that nevertheless leaves out other subtler layers that scientists are now beginning to identify in the deep interior of our planet.

A team of geologists has detected a previously unknown layer in the middle of the Earth’s mantle, whose characteristics are reminiscent of those of the planet’s surface.

Inner Earth Scientists Discover Mountains And Plains 370 Miles Beneath Earth’s Surface

A new study published in the Journal of Science, authored by geophysicists Jessica Irving and Wenbo Wu of Princeton University, in collaboration with Sidao Ni of the Institute of Geodesy and Geophysics of China, describes how researchers used data from the seismic waves of a large earthquake in Bolivia to locate, at a depth of 660 kilometers, a new region inside the Earth, one that has left them speechless: it features a mountain range, and plains, very similar to those on the surface of our planet.

And to be able to peer deep inside the planet, researchers had to make use of the most powerful waves that exist on our planet, the seismic waves generated by massive earthquakes.

“You want a big, deep earthquake to get the whole planet to shake,” said Irving, an assistant professor of geosciences.

For this particular study, the key data were obtained from seismic waves captured after an 8.2 magnitude earthquake, the second most powerful ever recorded, which shook Bolivia in 1994.

“Earthquakes this big don’t come along very often,” Irving said.

“We’re lucky now that we have so many more seismometers than we did even 20 years ago. Seismology is a different field than it was 20 years ago, between instruments and computational resources.”

But data alone is nothing if you don’t know how to make use of it.

That’s why scientists used the group of Tiger supercomputers from Princeton University to simulate the complex behavior of scattered seismic waves in the depths of the Earth.

The technology applied for this analysis depends almost entirely on a single property of the waves: its ability to bend and bounce.

Thus, in the same way, that light waves can bounce (reflect) in a mirror or bend (refract) when they pass through a prism, seismic waves travel directly through homogeneous rocks but are reflected or refracted when finding limits or roughness.

“We know that almost all objects have surface roughness and therefore scatter light,” said Wu, the lead author on the new paper, who just completed his geosciences Ph.D. and is now a postdoctoral researcher at the California Institute of Technology.

“That’s why we can see these objects — the scattering waves carry the information about the surface’s roughness. In this study, we investigated scattered seismic waves traveling inside the Earth to constrain the roughness of the Earth’s 660-km boundary.”

Scientists were left stunned by the roughness of the boundary. As they explain, its rougher than the surface layer we live on.

“In other words, stronger topography than the Rocky Mountains or the Appalachians exist at the 660-km boundary, explained Wu.

While the new study undoubtedly describes one of the most sensational discoveries made beneath our feet, their statistical model doesn’t offer much insight that could allow precise height determinations.

Nonetheless, scientists say that there’s a chance that some of these underground mountains are larger than anything we’ve seen on the surface of the planet.

They say that the roughness wasn’t equally distributed, either. According to scientists, just as the crust’s surface has smooth ocean floors and massive mountains, the 660-km boundary beneath our feet has rough areas and smooth patches.

from:    https://humansarefree.com/2020/07/inner-earth-scientists-discover-mountains-and-plains-370-miles-beneath-earths-surface.html

Puerto Rico Earthquake Zone

New undersea faults discovered near earthquake epicenters in southern Puerto Rico

New undersea faults discovered near earthquake epicenters in southern Puerto Rico

Seismologists from the United States Geological Survey (USGS) have found previously unknown undersea faults near the epicenters of earthquakes in Puerto Rico. The findings will help seismologists develop a clearer picture of tectonic activity in the area and give the public a clearer sense of the potential for future tremors.

In a news release published by the USGS, the agency announced that seafloor faults may have triggered the previous earthquake series on the island, which began December 28, 2019, including an M6.4 on January 7, 2020.

Earthquakes in southern Puerto Rico – May 2020. Credit: TW/SAM, Google. Data source: USGS

USGS said their seismologists were not surprised by the fact that earthquakes occurred but by where they occurred.

Puerto Rico lies on an active boundary between the Caribbean and North American plates, with the northeast corner of the Caribbean plate moving eastward about two centimeters (less than an inch) per year along a strike-slip fault. There is geologic evidence of earthquakes that probably took place millennia ago, while history records earthquakes and tsunamis in Puerto Rico as far back as the 1500s. But most seismic activity has been on the north side of the island, not the south side, where previously unknown undersea faults may have triggered this latest earthquake series.

“It seemed likely that a previously unknown fault system off the south coast was involved in the earthquake sequence, and there should be evidence of that on the seafloor,” said Uri ten Brink, a USGS research geophysicist.

“We thought that if that were true, the information would be potentially very valuable to science, and to the people of southern Puerto Rico. They are still recovering from the effects of Hurricane Maria, and now they are facing a completely different type of hazard, and they are hungry for information about it.”

Ten Brink, along with scientists from the University of Puerto Rico Mayaguez, ran a sequence of one-day research cruises out of the University of Puerto Rico Marine Station in La Parguera from March 7 to 13.

Preliminary findings confirm ten Brink’s assumptions that there is proof of at least one underwater fault in Guayanilla Bay, which might be an extension of a fault mapped previously on land.

Several more faults had been tentatively identified lying 7 and 15 km (4 and 9 miles) offshore, in waters up to about 1 000 m (3 300 feet) deep, also within areas identified as the epicenters of some of the latest earthquakes.


Locations of multichannel seismic reflection profiles (in black), collected during cruise FA2020-14. Image credit: Uri ten Brink, USGS

The team towed a device called “sparker” to map the faults, which uses an electrical charge to produce an air bubble in the sea. When the bubble expands, it generates a sound wave that travels through water and into the seabed, where geologic layers reflect some of the energy back to the surface. The research vessel also towed an array of 32 hydrophones below the sea surface to spot pressure changes underwater.

By measuring differences in the signals’ return, researchers can identify differences in the elevation of the rock beneath the seafloor. The differences, called offsets, are considered to be indications of faults that have been active recently.

The USGS team collected about 250 km (155 miles) of seismic reflection data, imaging the seabed and underwater structures at resolutions of just a few meters.

From the ship, several fresh scars were identified in shore-facing cliffs from Punta Montalva to Guayanilla Bay, which was caused likely by rockfalls due to the powerful tremors.

The team also searched for evidence of a fault breaking the seafloor at Punta Montalva, but the seismic data do not indicate clearly such a fault at first look.

Ten Brink said that in the following months, more sophisticated data processing is likely to unveil more faults, and the team expects to be able to measure ruptures along the faults.

“This data will eventually help seismologists develop a clearer picture of tectonic activity in the area,” he remarked. “Ultimately, we hope the USGS’ work in this region will help give the public a clearer sense of the potential for future earthquakes.”

“The USGS’ research findings are being used to improve building codes that will help Puerto Rico better withstand future earthquakes and to better prepare for tsunamis.”

Featured image credit: Uri ten Brink, USGS

from:    https://watchers.news/2020/05/31/new-undersea-faults-discovered-near-earthquake-epicenters-in-southern-puerto-rico/

A Quieter Earth

Coronavirus lockdowns have changed the way Earth moves

A reduction in seismic noise because of changes in human activity is a boon for geoscientists.



View down a road, featuring tram lines, with a tall building at the end.

Residents of Brussels have been told to stay at home, leaving the city’s streets empty.Credit: Jonathan Raa/NurPhoto via Getty

The coronavirus pandemic has brought chaos to lives and economies around the world. But efforts to curb the spread of the virus might mean that the planet itself is moving a little less. Researchers who study Earth’s movement are reporting a drop in seismic noise — the hum of vibrations in the planet’s crust — that could be the result of transport networks and other human activities being shut down. They say this could allow detectors to spot smaller earthquakes and boost efforts to monitor volcanic activity and other seismic events.

A noise reduction of this magnitude is usually only experienced briefly around Christmas, says Thomas Lecocq, a seismologist the Royal Observatory of Belgium in Brussels, where the drop has been observed.

Just as natural events such as earthquakes cause Earth’s crust to move, so do vibrations caused by moving vehicles and industrial machinery. And although the effects from individual sources might be small, together they produce background noise, which reduces seismologists’ ability to detect other signals occurring at the same frequency.

Source: Royal Observatory of Belgium

Data from a seismometer at the observatory show that measures to curb the spread of COVID-19 in Brussels caused human-induced seismic noise to fall by about one-third, says Lecocq. The measures included closing schools, restaurants and other public venues from 14 March, and banning all non-essential travel from 18 March (see ‘Seismic noise’).

The current drop has boosted the sensitivity of the observatory’s equipment, improving its ability to detect waves in the same high frequency range as the noise. The facility’s surface seismometer is now almost as sensitive to small quakes and quarry blasts as a counterpart detector buried in a 100-metre borehole, he adds. “This is really getting quiet now in Belgium.”

Information boost

If lockdowns continue in the coming months, city-based detectors around the world might be better than usual at detecting the locations of earthquake aftershocks, says Andy Frassetto, a seismologist at the Incorporated Research Institutions for Seismology in Washington DC. “You’ll get a signal with less noise on top, allowing you to squeeze a little more information out of those events,” he says.

The fall in noise could also benefit seismologists who use naturally occurring background vibrations, such as those from crashing ocean waves, to probe Earth’s crust. Because volcanic activity and changing water tables affect how fast these natural waves travel, scientists can study these events by monitoring how long it takes a wave to reach a given detector. A fall in human-induced noise could boost the sensitivity of detectors to natural waves at similar frequencies, says Lecocq, whose team plans to begin testing this. “There’s a big chance indeed it could lead to better measurements,” he says.

Belgian seismologists are not the only ones to notice the effects of lockdown. Celeste Labedz, a graduate student in geophysics at the California Institute of Technology in Pasadena, tweeted that a similar fall in noise had been picked up by a station in Los Angeles. “The drop is seriously wild,” she said.

However, not all seismic monitoring stations will see an effect as pronounced as the one observed in Brussels, says Emily Wolin, a geologist at the US Geological Survey in Albuquerque, New Mexico. Many stations are purposefully located in remote areas or deep boreholes to avoid human noise. These should see a smaller decrease, or no change at all, in the level of high-frequency noise they record, she says.

from:    https://www.nature.com/articles/d41586-020-00965-x?utm_source=fbk_nnc&utm_medium=social&utm_campaign=naturenews&fbclid=IwAR11iBTZdpp9A4EBjzBZEYLi8YihTj0cSFU-0y8y_xdothehyh1grqmkDqg?utm_source=wnd&utm_medium=wnd&utm_campaign=syndicated