Seismic gap may be filled by an earthquake near Istanbul

When a segment of a major fault line goes quiet, it can mean one of two things: The “seismic gap” may simply be inactive – the result of two tectonic plates placidly gliding past each other – or the segment may be a source of potential earthquakes, quietly building tension over decades until an inevitable seismic release.

Researchers from MIT and Turkey have found evidence for both types of behavior on different segments of the North Anatolian Fault – one of the most energetic earthquake zones in the world. The fault, similar in scale to California’s San Andreas Fault, stretches for about 745 miles across northern Turkey and into the Aegean Sea.

The researchers analyzed 20 years of GPS data along the fault, and determined that the next large earthquake to strike the region will likely occur along a seismic gap beneath the Sea of Marmara, some five miles west of Istanbul. In contrast, the western segment of the seismic gap appears to be moving without producing large earthquakes.

“Istanbul is a large city, and many of the buildings are very old and not built to the highest modern standards compared to, say, southern California,” says Michael Floyd, a research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “From an earthquake scientist’s perspective, this is a hotspot for potential seismic hazards.”

Although it’s impossible to pinpoint when such a quake might occur, Floyd says this one could be powerful – on the order of a magnitude 7 temblor, or stronger.

“When people talk about when the next quake will be, what they’re really asking is, ‘When will it be, to within a few hours, so that I can evacuate?’ But earthquakes can’t be predicted that way,” Floyd says. “Ultimately, for people’s safety, we encourage them to be prepared. To be prepared, they need to know what to prepare for – that’s where our work can contribute”

Floyd and his colleagues, including Semih Ergintav of the Kandilli Observatory and Earthquake Research Institute in Istanbul and MIT research scientist Robert Reilinger, have published their seismic analysis in the journal Geophysical Research Letters.

In recent decades, major earthquakes have occurred along the North Anatolian Fault in a roughly domino-like fashion, breaking sequentially from east to west. The most recent quake occurred in 1999 in the city of Izmit, just east of Istanbul. The initial shock, which lasted less than a minute, killed thousands. As Istanbul sits at the fault’s western end, many scientists have thought the city will be near the epicenter of the next major quake.

To get an idea of exactly where the fault may fracture next, the MIT and Turkish researchers used GPS data to measure the region’s ground movement over the last 20 years. The group took data along the fault from about 100 GPS locations, including stations where data are collected continuously and sites where instruments are episodically set up over small markers on the ground, the positions of which can be recorded over time as the Earth slowly shifts.

“By continuously tracking, we can tell which parts of the Earth’s crust are moving relative to other parts, and we can see that this fault has relative motion across it at about the rate at which your fingernail grows,” Floyd says.

From their ground data, the researchers estimate that, for the most part, the North Anatolian Fault must move at about 25 millimeters – or one inch – per year, sliding quietly or slipping in a series of earthquakes.

As there’s currently no way to track the Earth’s movement offshore, the group also used fault models to estimate the motion off the Turkish coast. The team identified a segment of the fault under the Sea of Marmara, west of Istanbul, that is essentially stuck, with the “missing” slip accumulating at 10 to 15 millimeters per year. This section – called the Princes’ Island segment, for a nearby tourist destination – last experienced an earthquake 250 years ago.

Floyd and colleagues calculate that the Princes’ Island segment should have slipped about 8 to 11 feet – but it hasn’t. Instead, strain has likely been building along the segment for the last 250 years. If this tension were to break the fault in one cataclysmic earthquake, the Earth could shift by as much as 11 feet within seconds.

Although such accumulated strain may be released in a series of smaller, less hazardous rumbles, Floyd says that given the historical pattern of major quakes along the North Anatolian Fault, it would be reasonable to expect a large earthquake off the coast of Istanbul within the next few decades.

“Earthquakes are not regular or predictable,” Floyd says. “They’re far more random over the long run, and you can go many lifetimes without experiencing one. But it only takes one to affect many lives. In a location like Istanbul that is known to be subject to large earthquakes, it comes back to the message: Always be prepared.”

Earthquake lights linked to rift environments, subvertical faults

Earthquake lights from Tagish Lake, Yukon-Alaska border region, around the 1st of July, probably 1972 or 1973 (exact date unknown). Estimated size: 1m diameter. Closest orbs slowly drifted up the mountain to join the more distant ones. -  Photo credit: Jim Conacher, used with permission
Earthquake lights from Tagish Lake, Yukon-Alaska border region, around the 1st of July, probably 1972 or 1973 (exact date unknown). Estimated size: 1m diameter. Closest orbs slowly drifted up the mountain to join the more distant ones. – Photo credit: Jim Conacher, used with permission

Rare earthquake lights are more likely to occur on or near rift environments, where subvertical faults allow stress-induced electrical currents to flow rapidly to the surface, according to a new study published in the Jan./Feb. issue of Seismological Research Letters.

From the early days of seismology, the luminous phenomena associated with some earthquakes have intrigued scholars. Earthquake lights (EQL) appear before or during earthquakes, but rarely after.

EQL take a variety of forms, including spheres of light floating through the air. Seconds before the 2009 L’Aquila, Italy earthquake struck, pedestrians saw 10-centimeter high flames of light flickering above the stone-paved Francesco Crispi Avenue in the town’s historical city center. On Nov. 12, 1988, a bright purple-pink globe of light moved through the sky along the St. Lawrence River near the city of Quebec, 11 days before a powerful quake. And in 1906, about 100 km northwest of San Francisco, a couple saw streams of light running along the ground two nights preceding that region’s great earthquake.

Continental rift environments now appear to be the common factor associated with EQL. In a detailed study of 65 documented EQL cases since 1600 A.D., 85 percent appeared spatially on or near rifts, and 97 percent appeared adjacent to subvertical faults (a rift, a graben, strike-slip or transform fault). Intraplate faults are associated with just 5 percent of Earth’s seismic activity, but 97 percent of documented cases of earthquake lights.

“The numbers are striking and unexpected,” said Robert Thériault, a geologist with the Ministère des Ressources Naturelles of Québec, who, along with colleagues, culled centuries of literature references, limiting the cases in this study to 65 of the best-documented events in the Americas and Europe.

“We don’t know quite yet why more earthquake light events are related to rift environments than other types of faults,” said Thériault, “but unlike other faults that may dip at a 30-35 degree angle, such as in subduction zones, subvertical faults characterize the rift environments in these cases.”

Two of the 65 EQL events are associated with subduction zones, but Thériault suggests there may be an unknown subvertical fault present. “We may not know the fault distribution beneath the ground,” said Thériault. “We have some idea of surface structures, but sedimentary layers or water may obscure the underlying fault structure.”

While the 65 earthquakes ranged in magnitude, from M 3.6 to 9.2, 80 percent were greater than M 5.0. The EQL varied in shape and extent, though most commonly appeared as globular luminous masses, either stationary or moving, as atmospheric illuminations or as flame-like luminosities issuing from the ground.

Timing and distance to the epicenter vary widely. Most EQL are seen before and/or during an earthquake, but rarely after, suggesting to the authors that the processes responsible for EQL formation are related to a rapid build-up of stress prior to fault rupture and rapid local stress changes during the propagation of the seismic waves. Stress-activated mobile electronic charge carriers, termed positive holes, flow swiftly along stress gradients. Upon reaching the surface, they ionize air molecules and generate the observed luminosities.

Eyewitness reports and security cameras captured a large number of light flashes during the 2007 Pisco, Peru M 8.0 earthquake. Together with seismic records obtained on a local university campus, the automatic security camera records allow for an exact timing and location of light flashes that illuminated a large portion of the night sky. The light flashes identified as EQL coincided with the passage of the seismic waves.

Thériault likes the account of a local L’Aquila resident, who, after seeing flashes of light from inside his home two hours before the main shock, rushed his family outside to safety.

“It’s one of the very few documented accounts of someone acting on the presence of earthquake lights,” said Thériault. “Earthquake lights as a pre-earthquake phenomenon, in combination with other types of parameters that vary prior to seismic activity, may one day help forecast the approach of a major quake,” said Thériault.

Devastating long-distance impact of earthquakes

In 2006 the island of Java, Indonesia was struck by a devastating earthquake followed by the onset of a mud eruption to the east, flooding villages over several square kilometers and that continues to erupt today. Until now, researchers believed the earthquake was too far from the mud volcano to trigger the eruption. Geophysicists at the University of Bonn, Germany and ETH Zurich, Switzerland use computer-based simulations to show that such triggering is possible over long distances. The results have been published in “Nature Geoscience.”

On May 27, 2006 the ground of the Indonesian island Java was shaking with a magnitude 6.3 earthquake. The epicenter was located 25 km southwest of the city of Yogyakarta and initiated at a depth of 12 km. The earthquake took thousands of lives, injured ten thousand and destroyed buildings and homes. 47 hours later, about 250 km from the earthquake hypocenter, a mud volcano formed that came to be known as “Lusi”, short for “Lumpur Sidoarjo”. Hot mud erupted in the vicinity of an oil drilling-well, shooting mud up to 50 m into the sky and flooding the area. Scientists expect the mud volcano to be active for many more years.

Eruption of mud volcano has natural cause

Was the eruption of the mud triggered by natural events or was it man-made by the nearby exploration-well? Geophysicists at the University of Bonn, Germany and at ETH Zürich, Switzerland investigated this question with numerical wave-propagation experiments. “Many researchers believed that the earthquake epicenter was too far from Lusi to have activated the mud volcano,” says Prof. Dr. Stephen A. Miller from the department of Geodynamics at the University of Bonn. However, using their computer simulations that include the geological features of the Lusi subsurface, the team of Stephen Miller concluded that the earthquake was the trigger, despite the long distance.

The overpressured solid mud layer was trapped between layers with different acoustic properties, and this system was shaken from the earthquake and aftershocks like a bottle of champagne. The key, however, is the reflections provided by the dome-shaped geology underneath Lusi that focused the seismic waves of the earthquakes like the echo inside a cave. Prof. Stephen Miller explains: “Our simulations show that the dome-shaped structure with different properties focused seismic energy into the mud layer and could very well have liquified the mud that then injected into nearby faults.”

Previous studies would have underestimated the energy of the seismic waves, as ground motion was only considered at the surface. However, geophysicists at the University of Bonn suspect that those were much less intense than at depth. The dome-like structure “kept” the seismic waves at depth and damped those that reached the surface. “This was actually a lower estimate of the focussing effect because only one wave cycle was input. This effect increases with each wave cycle because of the reducing acoustic impedance of the pressurizing mud layer”. In response to claims that the reported highest velocity layer used in the modeling is a measurement artifact, Miller says “that does not change our conclusions because this effect will occur whenever a layer of low acoustic impedance is sandwiched between high impedance layers, irrespective of the exact values of the impedances. And the source of the Lusi mud was the inside of the sandwich.”

It has already been proposed that a tectonic fault is connecting Lusi to a 15 km distant volcanic system. Prof. Miller explains “This connection probably supplies the mud volcano with heat and fluids that keep Lusi erupting actively up to today”, explains Miller.

With their publication, scientists from Bonn and Zürich point out, that earthquakes can trigger processes over long distances, and this focusing effect may apply to other hydrothermal and volcanic systems. Stephen Miller concludes: “Being a geological rarity, the mud volcano may contribute to a better understanding of triggering processes and relationships between seismic and volcanic activity.” Miller also adds “maybe this work will settle the long-standing controversy and focus instead on helping those affected.” The island of Java is part of the so called Pacific Ring of Fire, a volcanic belt which surrounds the entire Pacific Ocean. Here, oceanic crust is subducted underneath oceanic and continental tectonic plates, leading to melting of crustal material at depth. The resulting magma uprises and is feeding numerous volcanoes.

Earthquake acoustics can indicate if a massive tsunami is imminent, Stanford researchers find

On March 11, 2011, a magnitude 9.0 undersea earthquake occurred 43 miles off the shore of Japan. The earthquake generated an unexpectedly massive tsunami that washed over eastern Japan roughly 30 minutes later, killing more than 15,800 people and injuring more than 6,100. More than 2,600 people are still unaccounted for.

Now, computer simulations by Stanford scientists reveal that sound waves in the ocean produced by the earthquake probably reached land tens of minutes before the tsunami. If correctly interpreted, they could have offered a warning that a large tsunami was on the way.

Although various systems can detect undersea earthquakes, they can’t reliably tell which will form a tsunami, or predict the size of the wave. There are ocean-based devices that can sense an oncoming tsunami, but they typically provide only a few minutes of advance warning.

Because the sound from a seismic event will reach land well before the water itself, the researchers suggest that identifying the specific acoustic signature of tsunami-generating earthquakes could lead to a faster-acting warning system for massive tsunamis.

Discovering the signal


The finding was something of a surprise. The earthquake’s epicenter had been traced to the underwater Japan Trench, a subduction zone about 40 miles east of Tohoku, the northeastern region of Japan’s larger island. Based on existing knowledge of earthquakes in this area, seismologists puzzled over why the earthquake rupture propagated from the underground fault all the way up to the seafloor, creating a massive upward thrust that resulted in the tsunami.

Direct observations of the fault were scarce, so Eric Dunham, an assistant professor of geophysics in the School of Earth Sciences, and Jeremy Kozdon, a postdoctoral researcher working with Dunham, began using the cluster of supercomputers at Stanford’s Center for Computational Earth and Environmental Science (CEES) to simulate how the tremors moved through the crust and ocean.

The researchers built a high-resolution model that incorporated the known geologic features of the Japan Trench and used CEES simulations to identify possible earthquake rupture histories compatible with the available data.

Retroactively, the models accurately predicted the seafloor uplift seen in the earthquake, which is directly related to tsunami wave heights, and also simulated sound waves that propagated within the ocean.

In addition to valuable insight into the seismic events as they likely occurred during the 2011 earthquake, the researchers identified the specific fault conditions necessary for ruptures to reach the seafloor and create large tsunamis.

The model also generated acoustic data; an interesting revelation of the simulation was that tsunamigenic surface-breaking ruptures, like the 2011 earthquake, produce higher amplitude ocean acoustic waves than those that do not.

The model showed how those sound waves would have traveled through the water and indicated that they reached shore 15 to 20 minutes before the tsunami.

“We’ve found that there’s a strong correlation between the amplitude of the sound waves and the tsunami wave heights,” Dunham said. “Sound waves propagate through water 10 times faster than the tsunami waves, so we can have knowledge of what’s happening a hundred miles offshore within minutes of an earthquake occurring. We could know whether a tsunami is coming, how large it will be and when it will arrive.”

Worldwide application


The team’s model could apply to tsunami-forming fault zones around the world, though the characteristics of telltale acoustic signature might vary depending on the geology of the local environment. The crustal composition and orientation of faults off the coasts of Japan, Alaska, the Pacific Northwest and Chile differ greatly.

“The ideal situation would be to analyze lots of measurements from major events and eventually be able to say, ‘this is the signal’,” said Kozdon, who is now an assistant professor of applied mathematics at the Naval Postgraduate School. “Fortunately, these catastrophic earthquakes don’t happen frequently, but we can input these site specific characteristics into computer models – such as those made possible with the CEES cluster – in the hopes of identifying acoustic signatures that indicates whether or not an earthquake has generated a large tsunami.”

Dunham and Kozdon pointed out that identifying a tsunami signature doesn’t complete the warning system. Underwater microphones called hydrophones would need to be deployed on the seafloor or on buoys to detect the signal, which would then need to be analyzed to confirm a threat, both of which could be costly. Policymakers would also need to work with scientists to settle on the degree of certainty needed before pulling the alarm.

If these points can be worked out, though, the technique could help provide precious minutes for an evacuation.

The study is detailed in the current issue of the journal the Bulletin of the Seismological Society of America.

Fatal Mine Collapse Covered 50 Acres





This map shows the part of the Crandall Canyon Mine that was being mined in August, 2007, when a collapse occurred. A smaller collapse in March 2007 (red rectangle marked ‘March Damage’) forced coal miners out of the north barrier pillar. Mining later resumed in the south part of the mine. The solid red rectangle marked “Aug 6 Collapse” represents the Mine Safety and Health Administration’s original estimate of how much of the mine collapsed. A new study by University of Utah seismologists concludes the collapse covered an area four times larger, or 50 acres, represented by red-dashed rectangle. The new study also concludes the mine collapse’s ‘hypocenter’ — the underground point (red star) where a seismic event begins — was located very near where miners were working at the time of the collapse and near areas that had been mined during July and early August.

Seismology report: Disaster began near where miners worked



New calculations show that the deadly Crandall Canyon mine collapse – which registered as a magnitude-3.9 earthquake – began near where miners were excavating coal and quickly grew to a 50-acre cave-in, University of Utah seismologists say in a report on the tragedy.



The University of Utah Seismograph Stations estimated the size of the collapse is about four times larger than was thought shortly after the time of the Aug. 6, 2007, disaster that resulted in the deaths of six miners and, 10 days later, three rescuers.



The seismologists’ 53-page report has been submitted to the journal Seismological Research Letters and to federal Mine Safety and Health Administration (MSHA) investigators. Among the key findings:



  • Seismological and other data suggest the size of the area that collapsed in the nearly horizontal mine measured 920 meters (3,018 feet) from east to west – extending from about mine crosscut 143 to crosscut 120 – and measured 220 meters (722 feet) from north to south – a total of 50 acres. A crosscut is a north-south tunnel in this mine.
  • During the collapse, the space between the mine’s roof and floor decreased by an average of only 1 foot, but enough coal and rock exploded from the mine’s walls to fill much of the collapse area with rubble that likely prevented further collapse.
  • The collapse likely lasted only seconds – leaving no time for escape – and not for misery-prolonging minutes as some miners’ families have feared. The misconception arose from the fact seismic waves reverberate for much longer than the collapse or earthquake that generated them.
  • The mine collapse was followed in August by 37 measurable aftershocks, clustered near the east and inferred west ends of the collapse area, probably from post-collapse stress and from a vertical crack on the west end of the collapsed block of rock.
  • Seismologists recalculated the epicenter of the magnitude-3.9 mine collapse, and found it “was within the mine boundary and very close to where the miners were working,” says the study’s lead author, seismologist Jim Pechmann, a research associate professor of geology and geophysics at the University of Utah Seismograph Stations.


They did this “relocation” using new techniques, calibrated by data from five seismometers placed above and near the mine after the collapse and by the known location of the magnitude-1.6 coal “burst” on Aug. 16 that killed three rescuers and injured six others.



The epicenter is the point on the ground surface above a seismic event’s hypocenter, which is the underground point where the event begins.



The location of the preliminary epicenter calculated soon after the collapse was 0.4 miles outside the mine boundary and 0.6 miles to the west-southwest of the relocated epicenter. It was somewhat inaccurate partly because the nearest seismic station at the time of the collapse was 12 miles away, says seismologist Walter Arabasz, director of the University of Utah Seismograph Stations and a co-author of the new report. “That led some to conclude the seismic event was separate from the mine collapse.”



Arabasz and other seismologists insisted from the day of the collapse that available evidence indicated the magnitude-3.9 seismic event was the mine collapse itself. The mine’s owner argued it was a natural quake that triggered the collapse.



By showing the recalculated epicenter was within the mine boundary and near active mining, the new study adds strong evidence that the quake was the collapse itself.



“As seismologists, we’re as certain as we can be that the seismic event registered as a magnitude-3.9 shock was due to the collapse of the mine and not a naturally occurring earthquake,” Arabasz says.



Pechmann and Arabasz conducted the study with seismologists Kris Pankow and Relu Burlacu, both of the Seismograph Stations, and with Michael K. “Kim” McCarter, chair and professor of mining engineering at the University of Utah. The study was funded by the State of Utah and the U.S. Geological Survey.



Arabasz says all the information in the report has been given to MSHA investigators, but “we don’t have full access to their information, so we had to develop our interpretations, to a significant extent, independent of key information in the mine.”



Scientists usually don’t release studies until they are published in journals. But in this case, there have been numerous requests for the information, which is a matter of public interest, so researchers released the report now. They delayed the release a couple of weeks at MSHA’s request to give the agency time to inform disaster victims’ families.


Evidence of a Vertical Crack during the Mine Collapse



Soon after the Aug. 6 collapse, Utah seismologists gained support from University of California, Berkeley, and Lawrence Livermore National Laboratory seismologists, who said their analysis of the seismic recordings revealed implosive, downward movement – like a mine collapse and not like shearing motion along a fault.



The California seismologists also have submitted a report of their work to Seismological Research Letters. Pechmann says the new Berkeley paper shows that while seismic waves from the Aug. 6 mine collapse are incompatible with a natural earthquake, about 20 percent of the seismic energy released came from vertical shearing motion.



“The mostly likely explanation is a vertical, north-south crack in the roof of the mine that developed along the western edge of the collapse,” with the ground on the east side of the crack dropping downward, Pechmann says.



He emphasizes that seismic records show the shearing motion “did not occur at the start of collapse. It cannot be interpreted as an earthquake that triggered the collapse.”

Size of the Collapse



MSHA initially estimated the collapse extended 680 meters (2,231 feet) east to west – or from crosscut 137 to crosscut 120 – and at least 80 meters (262 feet) north to south, the study says, quoting an MSHA official. That is about 13 acres.



Pechmann says his team’s “model,” which shows a 50-acre collapse beginning at crosscut 143, is “based on seismological data, available underground observations, and constraints on how much collapse could occur given the amount of coal left in the pillars.



“It’s not the only possible scenario to describe the collapsed area, but it fits all the available data we have,” he adds. “The epicenter was near the western end of our proposed collapse area, suggesting the collapse started at the western end, and propagated mostly eastward” toward the mine entrance.



How did the calculated 1-foot roof collapse have such deadly consequences?



Pechmann says that within the collapsed area, only 37 percent of coal had been removed, and the rest was left behind in support pillars. “If those pillars shatter and covert to rubble – and if the coal increases 40 percent in volume when it shatters – then the closure you can get between the roof and the floor averages 0.3 meters [1 foot].” The roof can only collapse that far “because it gets stopped by the rubble,” he adds.


Collapse Began Near Where Miners Worked



The seismology report notes that the MSHA-approved 2007 amended mining plan called for removing coal from east-west tunnels called “entries” and from north-south tunnels, or crosscuts, leaving behind pillars about 110 feet long and 60 feet wide.



“The next phase of the plan was to mine coal in some of these pillars, working from west to east and allowing the roof around these pillars to collapse,” the report says.



The study shows the collapse hypocenter “was right at the edge of where miners were removing pillars in July and early August,” Pechmann says. The last known working location of the six miners was just east of where those pillars were removed.


How Long the Collapse Lasted



The report says: “Some people have interpreted a four-minute seismic signal duration reported for the Crandall Canyon main shock … as indicative of an extraordinarily long collapse duration. In reality, the duration of the collapse was probably only a few seconds, at most, as evidenced by reports that the surface building at the Crandall Canyon mine portal vibrated for a few seconds at the time.”



Seismologists could not directly measure how long the Aug. 6 collapse lasted, but note that seismic waves reverberate many times longer than an actual quake or collapse.



“The collapse probably happened within just a few seconds and was not a long, drawn-out affair,” Pechmann says. “There would have been no time for anybody to get out of the way. It would have happened too fast for that.”



He notes the deadly Aug. 16 “bump” that ended rescue efforts lasted a minute on seismographs, “but underground observers said it was essentially instantaneous.”


A History of Mine-Related Seismicity



Mining-induced seismicity is common in Utah’s Wasatch Plateau-Book Cliffs coal mining region, where more than 17,000 seismic events (most weaker than magnitude 3) were attributed to underground mining from 1978 through August 2007. Less than 2 percent of the area’s seismicity originates from natural earthquakes.



The researchers noted that from Jan. 1, 2007, until the Aug. 6 collapse and within 1.9 miles of it, there were 28 seismic events large enough to be detected and located. Of those, eight (all magnitude 1.9 or weaker) happened within 2.5 weeks before the collapse, and 15 (all 1.8 or less) happened in late February and early March.



“These events occurred primarily in areas where there was concurrent or recent mining activity,” the report states.



A large “bounce” on March 10, 2007, forced miners to abandon the north side of the active part of the mine due to damage in the event, and shift to the south side, where thicker pillars were left during mining but where the August tragedy occurred.



“We didn’t see any indication of accelerating seismic activity in the hours before the [Aug. 6] collapse,” Pechmann says. “We specifically looked for that.”



Afterward, many aftershocks likely were “continued failures of pillars supporting the roof due to stresses induced by the original collapse,” Pechmann says. “And some aftershocks may have been due to adjustments within the roof.”



The “Seismological Report on the 6 Aug. 2007 Crandall Canyon Mine Collapse in Utah” is available at: http://www.seis.utah.edu/