Ancient Temples In The Himalaya Reveal Signs Of Past Earthquakes

Tilted pillars, cracked steps, and sliding stone canopies in a number of 7th-century A.D. temples in northwest India are among the telltale signs that seismologists are using to reconstruct the extent of some of the region’s larger historic earthquakes.

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In their report published online July 27 in Seismological Research Letters, Mayank Joshi and V.C. Thakur of the Wadia Institute of Himalayan Geology show how the signs of destructive earthquakes are imprinted upon the ancient stone and wooden temples.

The temples in the Chamba district of Himachal Pradesh, India lie within the Kashmir “seismic gap” of the Northwest Himalaya range, an area that is thought to have the potential for earthquakes magnitude 7.5 or larger. The new analysis extends rupture zones for the 1905 Kangra earthquake (magnitude 7.8) and the 1555 Kashmir earthquake (possibly a magnitude 7.6 quake) within the Kashmir gap.

The type of damage sustained by temples clustered around two towns in the region—Chamba and Bharmour—suggests that the Chamba temples may have been affected by the 1555 earthquake, while the Bharmour temples were damaged by the 1905 quake, the seismologists conclude.

The epicenter of the 1555 earthquake is thought to be in the Srinagar Valley, about 200 kilometers northwest of Chamba. If the 1555 earthquake did extend all the way to Chamba, Joshi said, “this further implies that the eastern Kashmir Himalaya segment between Srinagar and Chamba has not been struck by a major earthquake for the last 451 years.”

The stress built up in this section of the fault, Joshi added, “may be able to generate an earthquake of similar magnitude to that of the 2005 Kashmir earthquake that devastated the eastern Kashmir.”

That magnitude 7.6 earthquake killed more than 85,000 people, mostly in north Pakistan, and caused massive infrastructure damage.

To better understand the historical earthquake record in the region, Joshi and Thakur examined several temples in the region to look for telltale signs of earthquake damage. It can be difficult at first to distinguish whether a tilted pillar, for example, is due to centuries of aging or to earthquake deformation.
But Joshi noted that archaeoseismologists are trained to look for regular kinds of deformation to a structure—damages “that have some consistency in their pattern and orientation,” said Joshi. “In the cases of aging and ground subsidence, there is no regular pattern of damage.”

At the temples, the researchers measured the tilt direction, the amount of inclination on pillars and the full temple structures, and cracks in building stones, among other types of damage. They then compared this damage to historic accounts of earthquakes and information about area faults to determine which earthquakes were most likely to have caused the damage.

“In the Chamba-area temples, there are some marker features that indicate that the body of the temple structure has suffered some internal deformation,” said Joshi. “The pillars and temple structures are tilted with respect to their original positions. The rooftop portions show tilting or displacement.”
Other earthquake damage uncovered by the researchers included upwarping of stone floors, cracked walls, and a precariously leaning fort wall.

“The deformation features also give some clues about the intensity of an earthquake,” Joshi explained. “For example if a structure experiences a higher intensity XI or X, then the structure could collapse. But if the structure is not collapsed but it tilts only, then it indicates that the structure experienced lower intensity of IX and VIII.”

The Mercalli intensity scale is a measurement of the observed effects of an earthquake, such as its impact on buildings and other infrastructure. Scale measurements of VIII (“severe”) and IX (“violent”) would indicate significant damage, while higher scale measurements indicate partial to complete destruction of buildings, roads, and other infrastructure.

Deep ‘Scars’ From Ancient Geological Events Play Role In Current Earthquakes

Super-computer modelling of Earth’s crust and upper-mantle suggests that ancient geologic events may have left deep ‘scars’ that can come to life to play a role in earthquakes, mountain formation, and other ongoing processes on our planet.

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This changes the widespread view that only interactions at the boundaries between continent-sized tectonic plates could be responsible for such events.

A team of researchers from the University of Toronto and the University of Aberdeen have created models indicating that former plate boundaries may stay hidden deep beneath the Earth’s surface. These multi-million-year-old structures, situated at sites away from existing plate boundaries, may trigger changes in the structure and properties at the surface in the interior regions of continents.

“This is a potentially major revision to the fundamental idea of plate tectonics,” says lead author Philip Heron, a postdoctoral fellow in Russell Pysklywec’s research group in U of T’s Department of Earth Sciences. Their paper, “Lasting mantle scars lead to perennial plate tectonics,” appears in the June 10, 2016 edition of Nature Communications.

Heron and Pysklywec, together with University of Aberdeen geologist Randell Stephenson have even proposed a ‘perennial plate tectonic map’ of the Earth to help illustrate how ancient processes may have present-day implications.

“It’s based on the familiar global tectonic map that is taught starting in elementary school,” says Pysklywec, who is also chair of U of T’s Department of Earth Sciences. “What our models redefine and show on the map are dormant, hidden, ancient plate boundaries that could also be enduring or “perennial” sites of past and active plate tectonic activity.”

To demonstrate the dominating effects that anomalies below the Earth’s crust can have on shallow geological features, the researchers used U of T’s SciNet — home to Canada’s most powerful computer and one of the most powerful in the world- to make numerical models of the crust and upper-mantle into which they could introduce these scar-like anomalies.

The team essentially created an evolving “virtual Earth” to explore how such geodynamic models develop under different conditions.

“For these sorts of simulations, you need to go to a pretty high-resolution to understand what’s going on beneath the surface,” says Heron. “We modeled 1,500 kilometres across and 600 kilometres deep, but some parts of these structures could be just two or three kilometres wide. It is important to accurately resolve the smaller-scale stresses and strains.”

Using these models, the team found that different parts of the mantle below the Earth’s crust may control the folding, breaking, or flowing of the Earth’s crust within plates — in the form of mountain-building and seismic activity — when under compression.

In this way, the mantle structures dominate over shallower structures in the crust that had previously been seen as the main cause of such deformation within plates.

“The mantle is like the thermal engine of the planet and the crust is an eggshell above,” says Pysklywec. “We’re looking at the enigmatic and largely unexplored realm in the Earth where these two regions meet.”

“Most of the really big plate tectonic activity happens on the plate boundaries, like when India rammed into Asia to create the Himalayas or how the Atlantic opened to split North America from Europe,” says Heron. “But there are lots of things we couldn’t explain, like seismic activity and mountain-building away from plate boundaries in continent interiors.”

The research team believes their simulations show that these mantle anomalies are generated through ancient plate tectonic processes, such as the closing of ancient oceans, and can remain hidden at sites away from normal plate boundaries until reactivation generates tectonic folding, breaking, or flowing in plate interiors.

“Future exploration of what lies in the mantle beneath the crust may lead to further such discoveries on how our planet works, generating a greater understanding of how the past may affect our geologic future,” says Heron.

The research carries on the legacy of J. Tuzo Wilson, also a U of T scientist, and a legendary figure in geosciences who pioneered the idea of plate tectonics in the 1960’s.

“Plate tectonics is really the cornerstone of all geoscience,” says Pysklywec. “Ultimately, this information could even lead to ways to help better predict how and when earthquakes happen. It’s a key building block.”

Likely Cause For Recent Southeast US Earthquakes: Underside Of The North American Plate Peeling Off

The southeastern United States should, by all means, be relatively quiet in terms of seismic activity. It’s located in the interior of the North American Plate, far away from plate boundaries where earthquakes usually occur. But the area has seen some notable seismic events — most recently, the 2011 magnitude-5.8 earthquake near Mineral, Virginia that shook the nation’s capital.

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Now scientists report in a new study a likely explanation for this unusual activity: pieces of the mantle under this region have been periodically breaking off and sinking down into the Earth. This thins and weakens the remaining plate, making it more prone to slipping that causes earthquakes. The study authors conclude this process is ongoing and likely to produce more earthquakes in the future.

“Our idea supports the view that this seismicity will continue due to unbalanced stresses in the plate,” said Berk Biryol, a seismologist at the University of North Carolina at Chapel Hill and lead author of the new study. “The [seismic] zones that are active will continue to be active for some time.” The study was published today in the Journal of Geophysical Research — Solid Earth, a journal of the American Geophysical Union.

Compared to earthquakes near plate boundaries, earthquakes in the middle of plates are not well understood and the hazards they pose are difficult to quantify. The new findings could help scientists better understand the dangers these earthquakes present.

Old plates and earthquakes

Tectonic plates are composed of Earth’s crust and the uppermost portion of the mantle. Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.

Earthquakes typically occur at the boundaries of tectonic plates, where one plate dips below another, thrusts another upward, or where plate edges scrape alongside each other. Earthquakes rarely occur in the middle of plates, but they can happen when ancient faults or rifts far below the surface reactivate. These areas are relatively weak compared to the surrounding plate, and can easily slip and cause an earthquake.

Today, the southeastern U.S. is more than 1,056 miles from the nearest edge of the North American Plate, which covers all of North America, Greenland and parts of the Atlantic and Arctic oceans. But the region was built over the past billion years by periods of accretion, when new material is added to a plate, and rifting, when plates split apart. Biryol and colleagues suspected ancient fault lines or pieces of old plates extending deep in the mantle following episodes of accretion and rifting could be responsible for earthquakes in the area.

“This region has not been active for a long time,” Biryol said. “We were intrigued by what was going on and how we can link these activities to structures in deeper parts of the Earth.”

A CAT scan of the Earth

To find out what was happening deep below the surface, the researchers created 3D images of the mantle portion of the North American Plate. Just as doctors image internal organs by tracing the paths of x-rays through human bodies, seismologists image the interior of the Earth by tracing the paths of seismic waves created by earthquakes as they move through the ground. These waves travel faster through colder, stiffer, denser rocks and slower through warmer, more elastic rocks. Rocks cool and harden as they age, so the faster seismic waves travel, the older the rocks.

The researchers used tremors caused by earthquakes more than 2,200 miles away to create a 3D map of the mantle underlying the U.S. east of the Mississippi River and south of the Ohio River. They found plate thickness in the southeast U.S. to be fairly uneven — they saw thick areas of dense, older rock stretching downward and thin areas of less dense, younger rock.

“This was an interesting finding because everybody thought that this is a stable region, and we would expect regular plate thickness,” Biryol said.

At first, they thought the thick, old rocks could be remnants of ancient tectonic plates. But the shapes and locations of the thick and thin regions suggested a different explanation: through past rifting and accretion, areas of the North American Plate have become more dense and were pulled downward into the mantle through gravity. At certain times, the densest parts broke off from the plate and sank into the warm asthenosphere below. The asthenosphere, being lighter and more buoyant, surged in to fill the void created by the missing pieces of mantle, eventually cooling to become the thin, young rock in the images.

The researchers concluded this process is likely what causes earthquakes in this otherwise stable region: when the pieces of the mantle break off, the plate above them becomes thinner and more prone to slip along ancient fault lines. Typically, the thicker the plate, the stronger it is, and the less likely to produce earthquakes.

According to Biryol, pieces of the mantle have most likely been breaking off from underneath the plate since at least 65 million years ago. Because the researchers found fragments of hard rocks at shallow depths, this process is still ongoing and likely to continue into the future, potentially leading to more earthquakes in the region, he said.

Rainwater May Play An Important Role In Process That Triggers Earthquakes

Rainwater may play an important role in the process that triggers earthquakes, according to new research.

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Researchers from the University of Southampton, GNS Science (New Zealand), the University of Otago, and GFZ Potsdam (Germany), identified the sources and fluxes of the geothermal fluids and mineral veins from the Southern Alps of New Zealand where the Pacific and Australian Plates collide along the Alpine Fault.

From careful chemical analyses, they discovered that fluids originating from the mantle, the layer below Earth’s crust, and fluids derived from rainwater, are channelled up the Alpine Fault.

By calculating how much fluid is flowing through the fault zone at depth, the researchers showed for the first time that enough rainwater is present to promote earthquake rupture on this major plate boundary fault.

Lead researcher Dr Catriona Menzies, from Ocean and Earth Science at the University of Southampton, said: “Large, continental-scale faults can cause catastrophic earthquakes, but the trigger mechanisms for major seismic events are not well known. Geologists have long suspected that deep groundwaters may be important for the initiation of earthquakes as these fluids can weaken the fault zones by increasing pressures or through chemical reactions.

“Fluids are important in controlling the evolution of faults between earthquake ruptures. Chemical reactions may alter the strength and permeability of rocks, and if enough fluid is present at sufficiently high pressures they may aid earthquake rupture by ‘pumping up’ the fault zone.”

The Alpine Fault is a major strike-slip fault, like the San Andreas, that fails in very large (Magnitude 8+) earthquakes around every 300 years. It last ruptured in 1717 AD and consequently it is under intense scientific scrutiny because it is a rare example of a major fault that is late in the strain-build up before rupture.

Dr Menzies said: “We show that the Alpine Fault acts as a barrier to lateral fluid flow from the high mountains of the Southern Alps towards the Tasman Sea in the west. However, the presence of mantle-derived fluids indicates that the fault also acts as a channel for fluids, from more than 35 km depth, to ascend to the surface.

“As well as mantle derived fluids, our calculations indicate that 0.02-0.05 per cent of surface rainfall reaches around six kilometres depth but this is enough to overwhelm contributions from the mantle and fluids generated during mountain-building by metamorphic reactions in hot rocks. This rainwater is then focused onto the fault, forced by the hydraulic head of the high mountains above and the sub-vertical fluid flow barrier of the Alpine Fault.”

Funding for this research, published in Earth and Planetary Science Letters, was provided by the Natural Environmental Research Council (NERC), Deutsche Forschungsgemeinschaft, and GNS Science (New Zealand).

BREAKING NEWS: Ecuador 7.8 Mag. Earthquake – Death Toll Jumps to 233; More Than 1,500 Wounded

The catastrophic earthquake that destroyed buildings in Ecuador on Saturday became far more devastating Sunday, when the death toll rose to 233 — and it’s expected to rise.

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Another 1,500 people were injured, said Ricardo Peñaherrera of Ecuador’s national emergency management office.

“It was the worst experience of my life,” survivor Jose Meregildo said Sunday about the tremors that violently shook his house in Guayaquil, 300 miles away from the quake’s epicenter.

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“Everybody in my neighborhood was screaming saying it was going to be the end of the world. Residents remain on the streets for fear of aftershocks in Pedernales on April 17.

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People make their way through debris from a collapsed building in Pedernales on Sunday, April 17. A magnitude-7.8 quake struck off Ecuador’s central coast on Saturday, April 16, flattening buildings and buckling highways. It’s the deadliest quake to strike the South

The magnitude-7.8 earthquake hit Saturday night as it buckled homes and knocked out power in Guayaquil, Ecuador’s most populous city, authorities said. Emergency officials recovered one body from the scene of a bridge collapse there.

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“Many highways are in bad shape, especially in the mountainous area because it has been raining recently due to (the) El Niño weather phenomenon.”

Vice President Jorge Glas had said earlier the death toll is expected to rise.

A state of emergency is in effect for six provinces — Guayas, Manabi, Santo Domingo, Los Rios, Esmeraldas and Galapagos. Authorities urged those who left their homes in coastal areas to return after a tsunami alert was lifted.

During his Sunday prayer, Pope Francis asked for those present to pray for the people affected by the earthquakes in Ecuador and Japan.

“Last night a violent earthquake hit Ecuador, causing numerous victims and great damages,” Francis said. “Let’s pray for those populations, and for those of Japan, where as well there has been some earthquakes in the last days. The help of God and of the brothers give them strength and support.”

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6.4 Magnitude Earthquake Hits Southwest Japan; Aftershocks Reported

TOKYO – A powerful earthquake with a preliminary magnitude of 6.4 struck Kyushu on Thursday, causing some damage but there was no danger of a tsunami.

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The Japan Meteorological Agency said the quake hit at 9:26 p.m. and was centered in the Mashiki town in the Kumamoto Prefecture where it registered the highest level of 7 on the Japanese seismic scale.

No abnormalities were reported at the Sendai nuclear power plant, officials said.

Keisukei Urata, an official at Uki city, said he was driving home when the quake struck. He said he saw some walls around houses collapsing.

Parts of the ceiling at Uki City Hall collapsed, windows were broken and cabinets fell to the ground, he said.

Kasumi Nakamura, an official in the village of Nishihara near the epicenter, said that the rattling started modestly and grew violent, lasting about 30 seconds.

“Papers, files, flower vases and everything fell on the floor,” he told a telephone interview with NHK TV. He said there were aftershocks.

One aftershock measuring 5.7 struck about 40 minutes later, while Kumamoot experienced an aftershock measuring a lower 6, according to Japan’s Meteorological Agency.

The U.S. Geological Survey put the quake’s preliminary magnitude at 6 and said it was 10 kilometers deep. It did not expect major damage.

Footage on NHK showed a signboard hanging from the ceiling at its local bureau violently shaking. File cabinets rattled, books, files and papers rained down to the floor, and one employee appeared to have fallen off a chair, while others slid underneath their desks to protect their heads.

Magnitude-6.9 Earthquake Hits Myanmar, Felt In India

A magnitude-6.9 magnitude earthquake hit Myanmar on Wednesday, the U.S. Geological Survey reported. There were no immediate reports of injuries, deaths or damage.

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The quake struck around 8:25 p.m. local time at a depth of 83.7 miles underground, USGS reported. Its epicenter was located 46 miles southeast of Mawlaik, in western Myanmar.

The quake was felt in the eastern Indian states of Assam and West Bengal, the Associated Press reported.

Quakes in the region typically are the result of the continental collision of the India and Eurasia plates.