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Thu, 24 Jun 2021
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Earthquakes

Bizarro Earth

Water causes the deep Earth's most mysterious earthquakes says research

Deep Earthquakes
© Illustration by Steven Shirey, Peter van Keken, Lara Wagner, and Michael Walter/Carnegie Institution for Science.
Some of Earth's largest earthquakes occur at tremendous depths (500-700 km) beneath the surface, always within or near oceanic plates that have sunk back into the Earth's interior. The cause of these events has been an enduring question in geology and geophysics for more than 40 years. In a new paper, a team of Carnegie and University of Alberta geoscientists provide several lines of evidence that fluids contribute to the genesis of deep earthquakes. New thermal modeling shows that carbonated crust and hydrated mantle in cold slabs can transport these fluids down to where deep earthquakes occur. Evidence from diamonds provides mineralogical proof of these mobile fluids in the mantle transition zone (440 - 670 km depth). This figure shows a sample thermal model of a subduction zone, with the relatively cold (blue) oceanic plate sinking into the comparatively hot (red) mantle. Three regions of earthquakes (grey spheres) visible in the oceanic plate: "intermediate-depth" dehydration-related earthquakes occurring between ~70 and ~250 km, a region of reduced seismicity between ~250 and ~350 km, and the region of "deep" seismicity below 350 km that extends to ~700 km. Superdeep diamonds (blue octahedra) are known to crystallize from fluids released in this deep region as the oceanic plate warms by the heat from the surrounding mantle.
Washington, DC — The cause of Earth's deepest earthquakes has been a mystery to science for more than a century, but a team of Carnegie scientists may have cracked the case.

New research published in AGU Advances provides evidence that fluids play a key role in deep-focus earthquakes — which occur between 300 and 700 kilometers below the planet's surface. The research team includes Carnegie scientists Steven Shirey, Lara Wagner, Peter van Keken, and Michael Walter, as well as the University of Alberta's Graham Pearson.

Most earthquakes occur close to the Earth's surface, down to about 70 kilometers. They happen when stress builds up at a fracture between two blocks of rock — known as a fault — causing them to suddenly slide past each other.

However, deeper into the Earth, the intense pressures create too much friction to allow this kind of sliding to occur and the high temperatures enhance the ability of rocks to deform to accommodate changing stresses. Though theoretically unexpected, scientists have been able to identify earthquakes that originate more than 300 kilometers below the surface since the 1920s.

"The big problem that seismologists have faced is how it's possible that we have these deep-focus earthquakes at all," said Wagner. "Once you get a few tens of kilometers down, it becomes incredibly difficult to explain how we are getting slip on a fault when the friction is so incredibly high."

Seismograph

M4.2 quake shakes Lake Tahoe, comes amidst uptick in activity in region

quake tahoe
A 4.2 magnitude earthquake has shaken the Lake Tahoe area Friday morning.

According to the US Geological Survey, the quake struck just before 8:30 a.m. and was centered about 5 miles southeast of the unincorporated community of Dollar Point.

This puts the epicenter of the quake right in the middle of Lake Tahoe.

Comment: On the 17th May CBS Sacramento reported that the increase in quakes appear to reflect the region being in an active period and that it may foreshadow larger quakes:
Frequent earthquakes across Northern California over the last several weeks have sparked questions about the natural disasters ahead.

State Geologist Steve Bohlen with California Geological Survey says the region has recently experienced earthquakes in rapid succession.

"We happen to be in a bit of an active period right now," said Bohlen.

At the end of April, a 3.8-magnitude earthquake hit the center of Lake Tahoe, followed by a 4.7-magnitude earthquake in Truckee, which was felt from Sacramento all the way to Reno.

"That was the biggest one I felt since I was out here. There were some lights and stuff swinging, something fell off the wall," said Ryan Callahan, who was at the Tourist Club in Truckee when the earthquake hit.

Seismologists tracking the activity say there's another, uncommon threat as well.

"There is a Tsunami hazard around Lake Tahoe," said Bohlen, who explains a magnitude-7 earthquake coming from the lake, though unlikely, could cause Tsunami-like waves.

"It would be significant emergency response effort in the Tahoe area if a magnitude-7 were to occur," he said.

How would you know if a Tsunami hit?

"If you feel an earthquake for [an] extended period of time, you really ought to think about moving to higher ground as quickly as possible," he said.

"It's an interesting idea thinking there could be a tsunami in Lake Tahoe," said Logan, who's visiting North Lake Tahoe this week.

But Tsunamis aren't something to sell your lakefront house over. Bohlen says just be prepared.

"Californians should have a safety kit with food, water...have a family plan of how to get together...when cellphones are down," he said.

An early warning system called Shake Alert could give precious extra seconds when an earthquake does hit.



Seismograph

Earthquakes in Congo raze buildings, stoke fear of second volcanic eruption

Lava from the eruption of Mount Nyiragongo
© AP
Lava from the eruption of Mount Nyiragongo cuts through Buhene north of Goma, Congo, May 24, 2021.
An earthquake on the border of Congo and Rwanda razed buildings in the city of Goma on Tuesday and stoked fears a nearby volcano would erupt again three days after dozens of people were killed and 17 villages were destroyed by lava.

The quake, measured at 5.3 magnitude by the Rwandan Seismic Monitor, was the largest of over 100 tremors that have followed the eruption on Saturday of Congo's Mount Nyiragongo volcano, one of the world's most active and dangerous.

"We know that children were injured when a building collapsed on Tuesday just a few steps from the UNICEF office in Goma," the U.N.children's agency said.

The quake appeared to have destroyed several buildings in the city of two million, and a witness said at least three people were pulled from the rubble and taken to hospital.

It struck at 11:03 a.m., originating in Rugerero sector in western Rwanda, according to the Rwanda Seismic Monitor.


Comment: Nyiragongo volcano erupts in DR Congo triggering evacuation in Goma - UPDATE


Seismograph

Major shallow magnitude 6.5 earthquake - Fiji: 266 Km SSE of Alo, Wallis And Futuna

Earthquake
© Associated Press
Date & time: 21 May 2021 22:13:18 UTC -

Local time at epicenter: 22 May 11:13 am (GMT +13)

Magnitude: 6.5

Depth: 10.0 km

Epicenter latitude / longitude: 16.6001°S / 177.3522°W (South Pacific Ocean, Fiji)

Seismograph

2 separate earthquakes strike China - one of magnitude 7.3 - three dead, dozens hurt

In this photo released by China's Xinhua News
© Hu Chao/Xinhua
In this photo released by China's Xinhua News Agency, medical workers treat a woman after an earthquake in Yangbi Yi Autonomous County in southwestern China's Yunnan Province, early Saturday, May 22, 2021. A pair of strong earthquakes struck two provinces in China overnight on Saturday.
A strong, shallow quake shook southwestern China near the border with Myanmar, killing at least three people and injuring more than two dozen, while a separate 7.3-magnitute quake early Saturday collapsed a bridge and caused other damage in central China.

The second quake hit the southern part of Qinghai province, about 1,000 kilometers (621 miles) north of the first quake in Yunnan province.

U.S. Geological Survey geophysicist Jonathan Tytell said the two quakes were not related.

The Qinghai temblor was followed by 453 aftershocks throughout the early morning into midday, according to the official People's Daily newspaper. At least eight people were injured.

While no deaths have been reported so far in Qinghai province, the quakes tore up roads and bridges, with one collapsing completely, broken into segments.


Seismograph

Shallow M6.7 earthquake hits Southern East Pacific Rise

quake map
© Volcano Discovery
Date & time: 19 May 2021 00:42:19 UTC - 6 hours ago
Magnitude: 6.7
Depth: 10.0 km
Epicenter latitude / longitude: 33.24°S / 109.57°W

Seismograph

Shallow M6.6 earthquake strikes off Indonesia's Sumatra

Sumatra earthquake map
© Volcano Discovery

An earthquake of magnitude 6.6 struck off the northwest coast of Indonesia's Sumatra island on Friday, the GFZ German Research Center for Geosciences (GFZ) said.

The Indonesia earthquake was at a depth of 10 km (6.21 miles), GFZ said.

Indonesia's weather and geophysics agency, BMKG, put the quake at 7.2 magnitude and at a depth of km but said it had no potential to trigger a tsunami wave.

On Dec. 26, 2004, a 9.1 magnitude quake off the coast of northwest Sumatra triggered a tsunami that killed more than 230,000 people in Indonesia, Sri Lanka, India, Thailand and nine other countries.

Seismograph

Strong M6.0 earthquake strikes off Japan's Fukushima prefecture

Japan earthquake map
© Volcano Discovery
A magnitude 6.0 earthquake has rattled northeastern Japan, but authorities have not issued a tsunami warning.

There were no immediate reports of casualties or damage to property on Friday and no abnormalities were found at the region's nuclear power facilities, including the crippled Fukushima Daiichi Nuclear Power Station, according to the Nuclear Regulation Authority.

The quake occurred at 8.58am (0958 AEST), its epicentre off the coast of Fukushima prefecture at a depth of 40 kilometres, the Meteorological Agency said.

In February, a magnitude-7.3 quake also struck the northeast, killing one person and injuring about 190 others.

Japan recently observed the 10th anniversary of the magnitude 9.0 quake and resulting tsunami in the same region on March 11, 2011, which left about 18,400 dead or missing.

Seismograph

Shallow 6.0 magnitude earthquake recorded off south coast of Panama

Earthquake
© Associated Press
An earthquake measuring a preliminary magnitude of 6.0 struck Thursday in waters off the south coast of Panama, according to the U.S. Geological Survey.

The quake was recorded around 9:42 GMT Thursday at a depth of 10 kilometers (6.2 miles) under the northern Pacific Ocean, some 150 kilometers (93 miles) southeast of Punta de Burica, Panama.

The USGS said little or no population was exposed to the quake. No tsunami warning has been issued.

No other details were immediately available.

Source: AP

Seismograph

Major shallow magnitude 6.6 earthquake - Mauritius/Reunion Region

quake
Major magnitude 6.6 earthquake at 10 km depth

Date & time: 12 May 2021 14:05:16 UTC -
Local time at epicenter: 12 May 6:05 pm (GMT +4)
Magnitude: 6.6
Depth: 10.0 km
Epicenter latitude / longitude: 17.31°S / 66.45°E