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.

World’s Largest Digital Sky Survey Issues Biggest Astronomical Data Release Ever

The Space Telescope Science Institute (STScI) in Baltimore, Maryland, in conjunction with the University of Hawai’i Institute for Astronomy (IfA), is releasing the second edition of data from Pan-STARRS—the Panoramic Survey Telescope & Rapid Response System—the world’s largest digital sky survey. This second release contains over 1.6 petabytes of data (a petabyte is 1015 bytes or one million gigabytes), making it the largest volume of astronomical information ever released. The amount of imaging data is equivalent to two billion selfies, or 30,000 times the total text content of Wikipedia. The catalog data is 15 times the volume of the Library of Congress.

The Pan-STARRS observatory consists of a 1.8-meter telescope equipped with a 1.4-billion-pixel digital camera, located at the summit of Haleakalā, on Maui. Conceived and developed by the IfA, it embarked on a digital survey of the sky in visible and near-infrared light in May 2010. Pan-STARRS was the first survey to observe the entire sky visible from Hawai’i multiple times in many colors of light. One of the survey’s goals was to identify moving, transient, and variable objects, including asteroids that could potentially threaten the Earth. The survey took approximately four years to complete, scanning the sky 12 times in five filters. This second data release provides, for the first time, access to all of the individual exposures at each epoch of time. This will allow astronomers and public users of the archive to search the full survey for high-energy explosive events in the cosmos, discover moving objects in our own solar system, and explore the time domain of the universe.

Dr. Heather Flewelling, a researcher at the Institute for Astronomy in Hawai’i, and a key designer of the PS1 database, stated that “Pan-STARRS DR2 represents a vast quantity of astronomical data, with many great discoveries already unveiled. These discoveries just barely scratch the surface of what is possible, however, and the astronomy community will now be able to dig deep, mine the data, and find the astronomical treasures within that we have not even begun to imagine.”

“We put the universe in a box and everyone can take a peek,” said database engineer Conrad Holmberg.

The four years of data comprise 3 billion separate sources, including stars, galaxies, and various other objects. This research program was undertaken by the PS1 Science Consortium—a collaboration among 10 research institutions in four countries, with support from NASA and the National Science Foundation (NSF). Consortium observations for the sky survey were completed in April 2014. The initial Pan-STARRS public data release occurred in December 2016, but included only the combined data and not the individual exposures at each epoch of time.

“The Pan-STARRS1 Survey allows anyone access to millions of images and catalogs containing precision measurements of billions of stars, galaxies, and moving objects,” said Dr. Ken Chambers, Director of the Pan-STARRS Observatories. “While searching for Near Earth Objects, Pan-STARRS has made many discoveries from ‘Oumuamua passing through our solar system to lonely planets between the stars; it has mapped the dust in three dimensions in our galaxy and found new streams of stars; and it has found new kinds of exploding stars and distant quasars in the early universe. We hope people will discover all kinds of things we missed in this incredibly large and rich dataset.”

The Space Telescope Science Institute hosts the storage hardware, the computers that handle the database queries, and the user-friendly interfaces to access the data. The survey data resides in the Mikulski Archive for Space Telescopes (MAST), which serves as NASA’s repository for all of its optical and ultraviolet-light observations, some of which date to the early 1970s. It includes all of the observational data from such space astrophysics missions as Hubble, Kepler, GALEX, and a wide variety of other telescopes, as well as several all-sky surveys. Pan-STARRS marks the nineteenth mission to be archived in MAST.

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.

UPDATE : Large Storm Hitting Central US, Heading East With Flooding Rain, Strong Winds

A large storm that developed in the central U.S. is moving east on Wednesday and bringing snow, a wintry mix, severe weather and flooding rain.

he storm dumped over 17 inches of snow in the mountains of Colorado, and widespread 2 to 4 inches of snow from the Colorado Plains to the upper Midwest. Freezing rain also was reported in parts of Iowa, Illinois and Indiana on Tuesday night.

Locally heavy snow is moving through parts of the Midwest, including Cedar Rapids, Iowa, and Milwaukee, Wisconsin, on Wednesday morning. In Chicago, a wintry mix, with some snow, is possible as colder air is being wrapped into the storm. However, most of the frozen precipitation will stay north and west of the city. A dangerous morning commute is likely in these areas.

Additionally, a wintry mix is likely across parts New York state Wednesday morning as precipitation is interacting with colder air.

There are numerous alerts being issued for this wide-ranging storm, including winter storm warnings and winter weather advisories from Kansas to Michigan to Maine. Since there is a threat for heavy rain in the Northeast, there are new flood watches being issued for the major cities, including New York, Philadelphia and Washington, D.C. Additionally, there are alerts being issued for blowing snow in the Northern Plains in the storm’s wake.

A line of very heavy rain will extend through the Mississippi and Tennessee Valley late in the day Wednesday. Additionally, severe weather is likely across parts of the Gulf — from New Orleans to Mobile — where damaging winds and brief tornadoes are possible. Since this cold front is very strong, it will also cause gusty winds over 35 mph in spots.

Out ahead of the cold front, very mild air will surge up the East Coast. Temperatures will be 10 to 20 degrees above average in the New York City area, where temperatures might be in the mid-50s Thursday morning. But the warmth will be brief.

Early Thursday morning, the heavy rain and strong winds will move into the southeast U.S. and toward Atlanta. By Thursday morning, the line of heavy rain, with some locally strong thunderstorms, will stretch along the entire East Coast. Very heavy rain will fall Thursday during morning rush hour in the major northeast cities. Locally, 1 to 2 inches of rain could cause flash flooding and strong gusty winds are possible.

An additional complication in parts of the Northeast is that the heavy rain, combined with mild temperatures, will cause last week’s snow to rapidly melt and cause additional flooding concerns.

Chill behind the storm

Behind this storm, another frontal system will pass and deliver a cold blast. Wind chills on Friday in the Midwest will dip locally to minus 30 degrees. Chicago will feel like minus 21 on Friday morning.

Some of this cold air makes its way east, but moderates before reaching the major Northeast cities. It will not be as cold as last weekend.

However, another powerful blast of cold air will come in behind it over the weekend and wind chills approaching minus 50 are possible in parts of the upper Midwest by Sunday. Duluth will feel like minus 47 and Minneapolis like minus 29 on Sunday morning — this is life-threatening cold.

Popocatepetl Volcano Erupts In Mexico

MEXICO, (CNN) — The Popocatepetl volcano registered a strong explosion Tuesday evening in the states of Puebla and Morelos, in central Mexico, according to Mexico’s civil protection authority.

The explosion caused lava and ashes to spew, with a smoke plume almost two miles high emanating from the volcano’s dome.

Authorities have asked locals to remain in their homes.

No initial reports of damages or injuries have been reported.