7.5 Magnitude Earthquake Strikes Ecuador-Peru Boarder

A powerful earthquake struck eastern Ecuador early Friday, sending tremors for miles through a sparsely populated area and into neighboring Peru and Colombia. The quake hit at an intermediate depth of about 82 miles, the U.S. Geological Survey said.

The earthquake struck at 5:17 a.m. local time. Its epicenter was 71 miles east-southeast of Palora, far inland and distant from Ecuador’s main highways that run along its mountain ranges.

“The Peru-Chile Trench is an area that hosts large earthquakes quite regularly,” the USGS said. It added that 15 other intermediate-depth earthquakes have occurred within 310 miles of the epicenter in the past 100 years.

Enormous Earthquake Reveals Hidden ‘Mountains’ 410 Miles Underground That Could Be Bigger Than Any On Earth’s Surface

In 1994, a huge 8.2-magnitude earthquake struck a sparsely populated region in Bolivia at a depth of around 400 miles below sea level. Now, an international team of scientists has analyzed data from this event to uncover previously unidentified “mountains” deep within Earth’s interior.

Most of us were taught in school that Earth is divided into different layers: an inner and outer core, the mantle and the crust. But this simplifies the picture slightly because, according to scientists, there is another layer called the “transition zone,” which splits the mantle in two.

For a study published in the journal Science, the team from Princeton University wanted to determine the roughness of the transition zones at the top and bottom—which lie at depths of 410 kilometers (255 miles) and 660 kilometers (410 miles) respectively. (The bottom of the transition zone is often referred to as the “660-km boundary.”)

To do this, the team had to look deep into Earth’s interior. But since we aren’t able to physically see below the surface, the scientists analyzed the behavior of shockwaves created by earthquakes as they scatter inside our planet to create a picture of what’s going on beneath the surface.

When it comes to this technique, the more powerful the earthquake the better, because stronger shockwaves can travel farther, hence why the team chose to examine the 1994 Bolivia event—the second largest deep quake ever recorded. In fact, shockwaves from quakes with a magnitude of 7.0 or higher are so powerful, that they can travel from one side of the planet to the other and back again.

“You want a big, deep earthquake to get the whole planet to shake,” Jessica Irving, an author of the study from Princeton, said in a statement. “Earthquakes this big don’t come along very often.”

Using Princeton’s Tiger supercomputer, the team examined shockwave data to determine what the top and bottom of the transition zone may look like. This technique works in a similar way to how our eyes enable us to see objects in the environment by detecting scattering light waves.

“We know that almost all objects have surface roughness and therefore scatter light,” said lead author of the study Wenbo Wu, from Princeton. “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 Earth to constrain the roughness of Earth’s 660-km boundary.”

Their results show that while the top of the transition zone is mostly smooth, the bottom is very rough in some places, such as the mountainous terrain on Earth’s surface.

“In other words, stronger topography than the Rocky Mountains or the Appalachians is present at the 660-km boundary,” Wu said.

While the scientists could not conduct precise measurements of the height of this terrain, they suggest that these mountains could potentially be bigger than anything similar on Earth’s surface.

Ultra-Slow Earthquake Indicates Deep Crustal Movement Near Istanbul

A big earthquake occurred south of Istanbul in the summer of 2016, but it was so slow that nobody noticed. The earthquake, which took place at mid-crustal depth, lasted more than fifty days. Only a novel processing technique applied to data from special borehole strainmeter instruments and developed by researchers from the GFZ German Research Centre for Geosciences, in collaboration with the Turkish Disaster and Emergency Management Presidency (AFAD) and the UNAVCO institute from US, allowed to identify the ultra-slow quake below the Sea of Marmara. The team led by Patricia Martínez-Garzón from GFZ’s section “Geomechanics and Scientific Drilling” reports in the journal Earth and Planetary Science Letters.

The region south of Istanbul is part of the North Anatolian Fault, separating Eurasia from the Anatolian plate. This geological fault is a large tectonic plate boundary known to generate destructive earthquakes causing large numbers of casualties. The last such major earthquake occurred in 1999 near Izmit causing almost 20,000 fatalities. A portion of the fault, running just south of the densely populated mega-city of Istanbul, is currently identified as a “seismic gap” and overdue to produce a large earthquake. While the tectonic loading due to plate motion is continuous thereby accumulating elastic energy on faults day-by-day, the release of the stored energy can occur either seismically in the form of earthquakes, or aseismically during fault creep or slow deformation at depth. Understanding the interaction between both phenomena is critically important to define the seismic hazard and subsequent risk in urban areas.

The study in Earth and Planetary Science Letters reports on a large 2-month lasting ultra-slow earthquake that occurred south of Istanbul below the Sea of Marmara in conjunction with elevated moderate-sized seismicity at shallow depth in the region. The researchers investigated the crustal deformation data from borehole instruments installed around the eastern Sea of Marmara as part of the GONAF Plate Boundary Observatory.

Data from one of the borehole strainmeter stations located in the most seismically active portion of the area on the Armutlu Peninsula was processed using novel computing techniques. ‘This allowed to identify the slow slip signal that presumably occurred at mid-crustal depth level and that is of the same size as the largest ever seen such signal that occurred along the San Andreas Fault in California’, says Dr. Martínez-Garzón, lead-author of the study. During this aseismic slow deformation signal the shallower and typically fully locked part of the earth crust responded by producing the highest number of moderate earthquakes in years indicating an interaction between near-surface and deep crustal deformation. Prof. Marco Bohnhoff, head of the GONAF observatory and a co-author of the study states: ‘How this interaction works remains to be understood in detail. In any case, our results will allow to better understand and quantify the regional seismic risk, in particular for the 15-million population center of Istanbul in the light of the pending big one’.

Deadly Earthquake Traveled At ‘Supersonic’ Speeds – Why That Matters

When the earthquake struck on September 28, 2018, Indonesia’s Sulawesi island flowed like water. Currents of mud swallowed anything in their paths, sweeping away entire sections of the city of Palu and crosscutting the region’s neat patchwork of crop fields. Minutes after the shaking began, locals were caught unaware by a wall of water that crashed onshore with devastating results.

As the sun set that evening, thousands were missing. Within days, the smell of corpses permeated the air. The 7.5-magnitude event was 2018’s deadliest quake, killing more than 2,000 people.

In the efforts to understand how this fatal series of events clicked into place, much attention has focused on the surprise tsunami. But a pair of new studies, published February 4 in Nature Geoscience, tackles another remarkable aspect: The earthquake itself was likely an unusual and incredibly fast breed of temblor known as supershear.

The Palu quake cracked through the earth at nearly 9,200 miles an hour—fast enough to get from LA to New York City in a mere 16 minutes. Such a fast rupture causes earthquake waves to pile up in what’s known as a Mach front, similar to the pressure wave from a plane traveling at supersonic speed. This concentrated cone of waves can amplify the quake’s destructive power.

“It’s like a sonic boom in an earthquake,” says Wendy Bohon, an earthquake geologist at the Incorporated Research Institutions for Seismology (IRIS).

While it’s not yet possible to say for sure if the supershear speed intensified the Indonesia quake’s landslides, liquefaction, or tsunami, the pair of new studies does offer a rare look at this little-understood and potentially deadly phenomenon.

“We have observed only a handful of supershear earthquakes, and even fewer with this level of detail,” says seismologist Jean-Paul Ampuero of the Université Côte d’Azur in France, a coauthor of one of the studies.

“This is going to tell us something fundamental about the way the Earth works,” says Bohon, who was not involved in either study. “And it has the potential to actually save lives and help us inform people in a better way.”

Unzipping the Earth
During an earthquake, the entire length of a fracture doesn’t break all at once. Rather, it unzips the planet’s surface at a rate known as the rupture speed.

Stephen Hicks, a seismologist at the University of Southampton, explains the phenomenon by grabbing a colorful flier sitting on a table at the American Geophysical Union Fall Meeting in Washington, D.C. He makes a tiny tear on one side, and says: “Imagine that’s your nucleation,” or the start of a rupture on a fault. The rupture speed is how fast that point moves through time, he says, and with a sharp jerk, he rips the flier in two.

It’s this speed that caught geologists’ attention with the Indonesia event. To take a closer look, Ampuero and his colleagues harnessed the power of the growing global network of seismic stations, which detect the echoes of earthquakes from hundreds of miles away. From that network, they collected data from 51 locations across Australia.

By studying the arrival of earthquake waves at each station, the team recreated the racing rupture. It’s similar to how your brain figures out where a sound is coming from, Ampuero explains. If someone is talking to you from the right, the noise arrives at your right ear a fraction of a second before your left. Your brain then uses that delay to locate the speaker.

“What we’re doing is the same, [but] instead of using only two ears we’re using hundreds of ears,” he says. “Each ear is one seismometer on the ground.”

This revealed that the temblor broke so fast that the rupture speed overtook a type of radiating waves known as shear waves, thus the term “supershear.” Over roughly 36 seconds, the quake cracked southward through some 93 miles of Earth’s surface.

“That is the ground breaking that fast, which is pretty amazing,” marvels Hicks, who wasn’t involved in the research.

Earthquake superhighway

A second team took a closer look at changes to the surface after the temblor ripped through, using data and imaging from satellites before and after the event.

“We were immediately struck by the sharpness of the rupture at the surface south of the city of Palu and by the great amount of displacement in this area,” study coauthor Anne Socquet, of the Université Grenoble Alpes in France, writes in an email.

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This analysis suggests that the land largely shifted horizontally, and that the change was massive: The ground offset by 16.4 feet at its maximum point south of Palu City. The shift was so large, it was easily seen in images of the region post-quake. Roads were offset; buildings seemingly cut in two.

“This is definitely huge for a [magnitude] 7.5 earthquake,” Socquet says. “And this is likely enhanced by the fact that this earthquake was supershear.” It didn’t happen just at the surface, either, but also as deep as roughly three miles underground.

In the southern stretches of the fault, an important feature behind this rapid speed and the deep shift is what Socquet calls its “maturity.” Tectonics have tested this break time and time again, continually shoving the blocks of Earth side by side and carving the fault into a fairly continuous, smooth, straight break—features previously associated with other examples of super-fast ruptures.

Anatomy of supershear

Yet even within this category of rare events, the Palu quake may stand apart. Most supershear earthquakes actually travel even faster than the one in Palu, cruising along almost as fast as another type of earthquake wave known as a pressure wave. These commonly zoom by around 11,200 miles an hour. But Ampuero and his colleagues found that while the Indonesia quake was fast enough to be supershear, it didn’t hit this top speed.

“It’s extremely rare to see events in this intermediate range,” he says.

Ampuero and his colleagues believe the discrepancy is due to the fact that earthquake models, including the one used in this work, commonly assume that the rocks surrounding a fault are one intact unit. But that’s not always the case in the real world, where zones of fractures around the break can slow the speeds of a quake’s associated waves through the surface.

If true for Sulawesi, this would mean the quake’s pressure waves could have moved about as fast as its rupture speed, as is expected for supershear ruptures. The quake was still weirdly slow for supershear, but at least its waves and rupture would have moved at the right relative speeds. However, the scientists won’t know for sure that this was the case without more study in the region.

That’s not the only thing unusual about the event. September’s earthquake also seemed largely undeterred by two major bends in the fault. Zigs and zags along the rupturing fault usually slow earthquakes, like cars on a winding road, but not this one. And unlike most supershear breaks, which need a little warmup, the Palu temblor seemed to hit its galloping pace early on.

“This earthquake is like a Lamborghini,” Bohon says. “It goes from zero to 60 in no time.”

This behavior raises even more questions. Could the fault be straighter at depth? This would have helped it barrel through bends higher up, Ampuero notes. Did smaller foreshocks supercharge the big quake? This could have sent it galloping out of the gates. But this early speed could also have to do with the roughness of the fault, which could stick the sides together like the rough sides of sandpaper and cause the ground to break with extra oomph.

More to come?
These unusual features make this earthquake all the more valuable, since they can help researchers better understand both where and how super-fast quakes can happen. The scientists who reviewed the work all stressed the significance of this information for future modeling and hazard assessments not just in Indonesia, but around the globe.

“What happened here could likely happen on other faults, especially major plate-boundary faults,” says Eric Dunham, a geophysicist at Stanford University.

“This type of fault is the same one we can find in California, Northern Turkey, Northern Aegean, the Dead Sea fault zone, Central Asia,” says earthquake geologist Sotiris Valkaniotis, who was not involved in the new studies. “The detections from this earthquake apply worldwide.”

6.6 Quake Hits Mexico; No Reports Of Deaths Or Serious Injuries

MEXICO CITY — A strong earthquake jolted southern Mexico on Friday, rattling nerves and swaying tall buildings hundreds of miles away in the capital, but there were no reports of serious damage, injuries or deaths.

 

The U.S. Geological Survey reported that the quake had a magnitude of 6.6. It was centered about 10 miles from the city of Tapachula in Chiapas state and struck at a depth of 40 miles.

Chiapas civil defense official Arturo Barrientos told The Associated Press that there were no reports of serious damage and authorities were monitoring the situation.

Barrientos said cracks appeared in a wall at an elementary school in the state capital, Tuxtla Gutierrez, but the children were evacuated safely.

“It was felt pretty strongly, but everything is normal. We went out into the street, and that was it,” Enrique Vidal, a lawyer who lives in Tapachula said via text message. “Those with children in schools went to look for them since there are buildings that are still damaged from 2017.”

The same region was rocked in September 2017 by a magnitude 8.1 earthquake that killed nearly 100 people and damaged thousands of buildings. A more damaging 7.1 quake in central Mexico later that month left more than 400 dead, including at least 228 in Mexico City.

“Fortunately there is no loss of human lives nor injuries that require hospitalization,” Luis Manuel Garcia, Chiapas’ civil defense secretary, told Foro TV. “Only nervousness.”

Friday’s quake was also felt in nearby Guatemala and farther away in El Salvador.

In Guatemala, the Red Cross reported some mud and rockslides along roads, and a bridge in the city of Quetzaltenango had some minor damage.

Along a central boulevard in Mexico City, which lies on lakebed soil that amplifies the effects of even faraway quakes, seismic alarms did not go off but some office workers briefly evacuated buildings.

Panicked Residents Flee Their Home As 6.6-Magnitude Earthquake Rocks Aru Islands

A 6.6-magnitude earthquake rocked the Aru Islands, Maluku, on Saturday at 5:12 p.m. local time, prompting residents to run out of their homes.

Two buildings were damaged. No injuries or casualties have been reported.

The earthquake’s epicenter was detected northwest off the coast of Dobo, the center of the archipelagic regency, and at a depth of 10 kilometers. Tremors were felt as far away as Timika, Papua.

They were strong enough to lightly damage a house and a hospital in Dobo, according to the National Disaster Mitigation Agency (BNPB).

“All of us ran outside because the tremors were strong,” said Dobo resident Demy as quoted by kompas.com.

He also said that the earthquake lasted almost 10 seconds.

Local authorities are still assessing the extent of the damage caused by the earthquake.

Earthquake: 6.2 Quake Strikes Near Taro, Solomon Islands

A deep magnitude 6.2 earthquake was reported Friday evening 22 miles from Taro, Solomon Islands, according to the U.S. Geological Survey. The temblor occurred at 7:51 p.m. Pacific time at a depth of 221.8 miles.

According to the USGS, the epicenter was 73 miles from Arawa, Papua New Guinea.

In the last 10 days, there have been no earthquakes of magnitude 3.0 or greater centered nearby.