Category: Earthquakes

Model Suggests 1812 San Andreas Earthquake May Have Been Set Off By San Jacinto Quake

An assistant researcher professor with California State University has found evidence that the powerful quake that struck southern Californian back in 1812 may have been precipitated by a fault line other than the San Andreas. In his paper published in the journal Science Advances, Julian C. Lozos describes a computer model he created using real world data, what it showed, and why his findings suggest that a future double earthquake could occur someday in the area.

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Back in 1812 a major earthquake struck southern California near what is now San Bernardino—modern study of damage from the quake suggested it was approximately a magnitude 7.5 quake. There was little damage because there were few structures in the area back then, though approximately 40 people were killed when a church they were in collapsed. For many years, Earth scientists have assumed that the quake was due solely to activity along the San Andreas Fault. In this new effort, Lozos suggests that the quake may have actually been set off by a quake along the San Jacinto fault line.

Lozos’ findings are part of a study that included field trips to several sites in an area where the San Andreas Fault and the San Jacinto Fault nearly merge. While there, he found evidence of three strands—where sections of fault are separated by bits of crust that has remained intact—one near the San Andreas fault and two near the San Jacinto fault. Each strand is evidence of an earthquake, but reports from people in the area suggest there were only two earthquakes during the time period under study—in 1812 and 1800, which suggested that one of the strands on the San Andreas Fault and one on the San Jacinto Fault were evidence of the same quake. Lozos also looked at other data collected by other researchers doing working on faults in the area—all of it went into a model he built to describe seismic activity in the area surrounding the time frame of the 1812 quake. The model showed that the most likely scenario that could account for the data that has been collected was that a quake had occurred along the San Jacinto fault line and as it made its way near the San Andreas fault line, the disruption caused a quake to occur along that fault line as well.

Lozos is quick to point out that his model is just that and that thus far he has no evidence to suggest that such a double quake is imminent, but he also notes that if it happened before, it could happen again, noting that southern California is long overdue for a pretty big tumbler.

New Study Pinpoints Stress Factor Of Mega-Earthquake Off Japan

Scripps Institution of Oceanography, UC San Diego researchers published new findings on the role geological rock formations offshore of Japan played in producing the massive 2011 Tohoku-oki earthquake, one of only two magnitude 9 mega-earthquakes to occur in the last 50 years.

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The study, published in the journal Nature, offers new information about the hazard potential of large earthquakes at subduction zones, where tectonic plates converge.

The magnitude 9 quake, which triggered a major tsunami that caused widespread destruction along the coastline of Japan, including the Fukushima nuclear plant disaster, was atypical in that it created an unusually large seismic movement, or slip, of 50 meters (164 feet) within a relatively small rupture area along the earthquake fault.

To better understand what may have caused this large movement, Scripps researchers used gravity and topography data to produce a detailed map of the geological architecture of the seafloor offshore of Japan. The map showed that the median tectonic line, which separates two distinct rock formations, volcanic rocks on one side and metamorphic rocks on the other, extends along the seafloor offshore.

The region over the earthquake-generating portion of the plate boundary off Japan is characterized by variations in water depth and steep topographic gradients of about six kilometers (3.7 miles). These gradients, according to the researchers, can hide smaller variations in the topography and gravity fields that may be associated with geological structure changes of the overriding Japan and subducting Pacific plates.

“The new method we developed has enabled us to consider how changes in the composition of Japan’s seafloor crust along the plate-boundary influences the earthquake cycle,” said Dan Bassett, a postdoctoral researcher at Scripps and lead author of the study.

The researchers suggest that a large amount of stress built up along the north, volcanic rock side of the median tectonic line resulting in the earthquake’s large movement. The plates on the south side of the line do not build up as much stress, and large earthquakes have not occurred there.

“There’s a dramatic change in the geology that parallels the earthquake cycle,” said Scripps geophysicist David Sandwell, a co-author of the study. “By looking at the structures of overriding plates, we can better understand how big the next one will be.”

Earthquakes On Thrust Faults Can Spread 10 Times Farther To A Second Nearby Thrust Fault Than Previously Thought

A team of researchers, including one from the University of California, Riverside, has discovered that earthquake ruptures can jump much further than previously thought, a finding that could have severe implications on the Los Angeles area and other regions in the world.

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The scientists found that an earthquake that initiates on one thrust fault can spread 10 times farther than previously thought to a second nearby thrust fault, vastly expanding the possible range of “earthquake doublets,” or double earthquakes.

That could mean in areas such as Los Angeles, where there are multiple thrust faults close to each other, an earthquake from one thrust fault could spread to another fault, creating twice as much devastation.

One potential bad scenario involves a single earthquake spreading between the Puente Hills thrust fault, which runs under downtown Los Angeles, and the Sierra Madre thrust fault, located close to Pasadena, said Gareth Funning, an associate professor of earth sciences at UC Riverside, and a co-author of a paper published online today (Feb. 8, 2016) about the research in the journal Nature Geoscience.

Other susceptible areas where there are multiple thrust faults are in close proximity include the Ventura, Calif. area, the Middle East, particularly Tehran, Iran, and the front of the Himalayas, in countries such as Afghanistan, Pakistan, India and Nepal.

The researchers studied a 1997 earthquake in Pakistan, originally reported as a magnitude 7.1 event, showing that it was in fact composed of two ‘subevents’—a magnitude 7.0 earthquake, that was followed 19 seconds later by a magnitude 6.8 event, located 50 kilometers (30 miles) to the southeast.

Funning considers the two earthquakes as subevents of one ‘mainshock,’ as opposed to the second earthquake being an aftershock, because they happened so close together in time and were so similar in size. There were many aftershocks in the following minutes and hours, but most of them were much smaller.

The scientists used satellite radar images, precise earthquake locations, modeling and back projection of seismic radiation to prove the seismic waves from the first subevent caused the second to initiate, effectively ‘jumping’ the 50 kilometer distance between the two. Scientists previously thought an earthquake could only leap up to five kilometers.

The finding has implications for seismic hazard forecasts developed by the United States Geological Survey. The current forecast model does not include the possibility of a similar double earthquake on the thrust faults in the Los Angeles area.

“This is another thing to worry about,” Funning said. “The probability of this happening in Los Angeles is probably pretty low, but it doesn’t mean it can’t happen.”
Funning started work on the paper about 12 years ago as a graduate student at the University of Oxford. He was the first to find the satellite data for the earthquakes in Pakistan, which occurred in a largely unpopulated area, and notice they occurred close together in space and time.

After dropping the work for several years, he, along with lead author Ed Nissen of the Colorado School of Mines, picked it up about three to four years ago, in part because of the possible implications for the Los Angeles area, which has a similar plate boundary, with similar faults, similar distances apart as the region in Pakistan where the 1997 earthquake doublet occurred.

Thrust faults happen when one layer of rock is pushed up over another, often older, layer of rock by compressional forces. Thrust faults came to the attention of Californians after the 1994 Northridge earthquake, about 20 miles northwest of Los Angeles, which occurred on a thrust fault.

Thrust faults are not as well understood by scientists as strike-slip faults, such as the San Andreas, in part because they are not as visible in the landscape, and do not preserve evidence for past earthquakes as well.

Researchers Find New Cause of Strong Earthquakes

A geologic event known as diking can cause strong earthquakes—with a magnitude between 6 and 7, according to an international research team.

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Diking can occur all over the world but most often occurs in areas where the Earth’s tectonic plates are moving apart, such as Iceland, Hawaii and parts of Africa in the East African Rift System. As plates spread apart, magma from beneath the Earth’s surface rises into the space, forming vertical magma intrusions, known as dikes. The dike pushes on the surrounding rocks, creating strain.

“Diking is a known phenomenon, but it has not been observed by geophysical techniques often,” said Christelle Wauthier, assistant professor of geosciences, Penn State who led the study. “We know it’s linked with rift opening and it has implications on plate tectonics. Here, we see that it also could pose hazards to nearby communities.”
The team investigated ties between two natural disasters from 2002 in the Democratic Republic of the Congo, East African Rift System. On Jan. 17, the Nyiragongo volcano erupted, killing more than 100 people and leaving more than 100,000 people homeless. Eight months later a magnitude 6.2 earthquake struck the town of Kalehe, which is 12 miles from the Nyiragongo volcano. Several people died during the Oct. 24 earthquake, and Kalehe was inundated with water from nearby Lake Kivu.

“The Kalehe earthquake was the largest recorded in the Lake Kivu area, and we wanted to find out whether it was coincidence that, eight months before the earthquake, Nyiragongo erupted,” said Wauthier.

The researchers used a remote sensing technique, Interferometric Synthetic Aperture Radar, to measure changes to the Earth’s surface before and after both natural disasters.

“This technique produces ground surface deformation maps. Then, you can invert those deformation maps to find a source that could explain the observed deformation. For the deformation observed in January 2002, we found that the most likely explanation, or best-fitting model, was a 12-mile diking intrusion in between Nyiragongo and Kalehe,” said Wauthier.

The researchers used the same technique for the October 2002 magnitude 6.2 earthquake, analyzing seismicity in addition to ground-deformation changes. They found that there was a fault on the border of the East African Rift System that slipped, triggering the earthquake.

“We were able to identify the type of fault that slipped, and we also had the best-fitting model for the dike intrusion,” said Wauthier. “Knowing both of those, we performed a Coulomb stress-change analysis and found that the January 2002 dike could have induced the October 2002 earthquake.”

Coulomb stress-change analysis is a modeling technique that calculates the stress changes induced by a deformation source at potential receiver faults throughout a region. If the Coulomb stress changes are positive, it means that the source is bringing the receiver fault closer to failure—closer to slipping and generating an earthquake. This type of analysis is regularly applied to assess whether an earthquake in one region could trigger a secondary earthquake nearby.

The researchers hypothesized that the dike opening pushed outward against the adjacent rocks. These rocks became strained and passed stress to rocks adjacent to them, accumulating stress on rocks on a fault in the Kalehe area. The dike brought this fault closer to failure and, eight months later, a small stress perturbation could have triggered the start of the magnitude 6.2 earthquake.

“We’ve known that every time magma flows through the Earth’s crust, you create stress and generate seismicity,” said Wauthier. “But these are normally very low magnitude earthquakes. This study suggests that a diking event has the potential to lead to a large earthquake,” said Wauthier.

The researchers report their findings in the current issue of Geochemistry, Geophysics, Geosystems.

Dozens Still Trapped A Day After Taiwan Earthquake

TAINAN, Taiwan – With anxious families waiting nearby, rescuers on Sunday painstakingly pulled more survivors from the remains of a high-rise apartment building that collapsed a day earlier in a powerful earthquake that shook southern Taiwan and killed at least 26 people. More than 100 remained buried in the building’s rubble.

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The government in Tainan, the worst-hit city, said that more than 170 people had been rescued from the 17-story building, which folded like an accordion after the quake struck.

Mao Yi-chen, 20, was rescued soon after the magnitude-6.4 quake hit before dawn Saturday, and her older sister Mao Yi-hsuan was pulled out Sunday in serious condition. A rescue worker had handed over a photo album and homemade cards found next to her for her family to collect, said local official Wang Ding-yu.

“He said that ‘maybe your home is damaged, but memories of the family can last,'” Wang said.

Tainan Mayor Lai Ching-te said authorities estimated that 124 people were still trapped, many at the bottom of the wreckage. He said rescuers were able to reach many people by using information from residents who got out about the possible locations of those still inside.

Wendy Chuang, a reporter in Taiwan, told CBS Radio News that the building was unrecognizable.

“Actually if no one told me, it’s hard to tell that’s a building because it just fell down and you can’t tell which way it fell down actually,” Chuang said. “You can’t find where’s the doors, where’s the front, where’s the back.”

Two of the trapped, a male and a female at different sides of the building, were talking to rescue workers on Sunday evening, Lai said. He told reporters that rescuers intended to pull them out, and then bring in heavier excavators to remove part of the structure on top to allow access to the areas at the bottom.

The spectacular fall of the high-rise, built in 1989, raised questions about whether its construction had been shoddy. Tainan’s government said the building had not been listed as a dangerous structure, and Taiwan’s interior minister, Chen Wei-zen, said an investigation would examine whether the developer had cut corners.

Eighth-floor resident Huang Guang-wei was pulled out Sunday morning from a different section from where he lived, showing how distorted the building is, Lai said. Rescuers could see Huang only through a 10-centimeter (4-inch) crack and it took eight hours to get him out, Lai said.

Among the fatalities was a 6-month-old baby girl who was pulled from the rubble and rushed to a hospital, where she was pronounced dead. A deceased man believed to be her father was pulled out 40 minutes later, Wang said.

A man in his 60s, whose son escaped and whose daughter-in-law was in serious condition, was trying to help rescuers pinpoint his grandsons. “My 11- and 12-year-old grandsons are still inside on the ninth floor,” said the man, who gave only his surname, Huang. “I told my son not to buy an apartment here; it was suspiciously cheap.”

Beside him, another man nodded in agreement as he waited for news of his own relatives on the seventh floor.

The city government said that 24 of the 26 confirmed deaths from the earthquake were from the building collapse. It said that 171 had been rescued from the building, 91 of whom were sent to hospitals. More than 100 people were rescued from other parts of Tainan, eight of whom received hospital treatment. Nine other buildings in the city collapsed and five careened.

On Sunday, thousands of rescuers worked on different levels of the folded building, which was supported by steel pillars. Rescuer Su Yu-min said they were trying to cut through walls and pillars.

“It takes a few hours to complete a search for just one household and sometimes it takes two hours just to go forward 30 centimeters (12 inches)” when the way is blocked by a wall, he said.

Taiwanese broadcaster EBC showed video of volunteers trying to comfort the mother of a missing 20-year-old man, Chen Guan-yu. “He always thinks of me,” said the woman, whose name was not given. “He worries about me being single and lonely and that no one is taking care of me.”

The quake came two days before the start of Lunar New Year celebrations that mark the most important family holiday in the Chinese calendar.

Earthquakes frequently rattle Taiwan, but most are minor and cause little or no damage, though a magnitude-7.6 quake in central Taiwan in 1999 killed more than 2,300 people.

Taiwan Earthquake: Tainan Hit By 6.4-Magnitude Quake

The death toll was rising in the historic city of Tainan, which bore the brunt of the 6.4-magnitude quake, as rescuers scoured rubble for survivors.

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Nearly 340 people were rescued from the rubble in Tainan, the city hit worst by the quake. About 2,000 firefighters and soldiers scrambled with ladders, cranes and other equipment to the ruins of the 17-floor residential building, which folded like an accordion onto its side after the quake struck.

Local authorities said Saturday night that more than 100 people remained missing and that rescuers were racing to find them. Taiwan’s official Central News Agency reported that 172 people were missing.

An entire residential complex of four buildings containing almost 100 homes toppled, left on its side with twisted metal girders exposed and clouds of dust rising from the jumbled concrete.

The official CNA news agency reported that the quake killed 14 people and injured 484 others, according to statistics by Taiwan’s rescue authorities. Most of the injured had been released from hospitals by Saturday night.

CNA said 153 people remained missing and that rescuers were racing to find them. Taiwan’s SETV reported that 101 adults and 41 children were missing. The number of missing was expected to drop because some of those listed might have been listed twice, hospitalized or not in the building at the time of the quake.

Rescuer Jian Zhengshun said the rescue work was difficult because part of the high-rise building was believed to be buried underground, with the quake loosening the earth. He said rescuers had to clear rubble for passages to reach people who were trapped.

Rescuers found the bodies of a 10-day-old infant, three other children and six adults at the collapsed building, the information center said. One other death was reported at the site, but details were not immediately available.

Authorities said two people were killed by falling objects elsewhere in Tainan.

Officials said four buildings collapsed in the quake which struck the island in the early hours of the morning, but rescue efforts are centring on the tower block that tumbled onto its side.

Firefighters pulled survivors from the twisted concrete, trying to access apartments through windows and scaling the rubble with ladders.

Around 800 troops have been mobilised to help the rescue effort, with sniffer dogs also searching through the rubble.

The baby, a man and a woman were pulled dead from the block, officials said, with 29 residents taken to hospital.

“These three people showed no signs of life before they were sent to the hospital,” said Lin Kuan-cheng, spokesman for the National Fire Agency.

“The search and rescue work continues there, home by home.”

Residents at the felled Wei-kuan Building told of their terror as the quake hit, with survivors pulled bleeding and crying from the ruins, some just in their underwear.

“I saw buildings shake up and down and left and right,” said one resident. “The first and second floor just collapsed,” he told local channel SET TV. Another man tied his clothes together to create a rope and lowered himself from his home on the ninth floor to the sixth floor below, Apple Daily reported.

One woman told how she had fought her way out of her home.

“I used a hammer to break the door of my home which was twisted and locked, and managed to climb out,” she told SET TV, weeping as she spoke.

Rescuers have freed more than 250 people from the apartment complex, with over 40 of them hospitalised.

Interior minister Chen Wei-jen said he feared there may be more people in the building than usual as family members would have returned to celebrate the Lunar New Year holidays next week.

“We are concerned that most members of those families may have returned for the coming new year holiday,” he said.

Heartfelt appeals for the missing were posted on social media. “My friend in Wei-kuan is currently missing. His brother is waiting at the scene and other relatives are at the hospital looking among those injured. If anyone has related news, please get in touch,” one user called applexgreen posted on Taiwan’s popular PTT forum.

Another named Ahan asked for information on a family of three with a two-year-old son who lived on the seventh floor of the building.

“My mother is the child’s nanny. We haven’t been able to get in contact,” the post said.

Officials were unable to give an estimate of how many were still trapped as they scoured the building.

As dawn broke, live Taiwanese TV showed survivors being brought gingerly from the building, including an elderly woman in a neck brace and others wrapped in blankets.

The trappings of daily life — a partially crushed air conditioner, pieces of a metal balcony, windows — lay twisted in what appeared to be nearby rubble.

People with their arms around firefighters were being helped from the building, and cranes were being used to search darkened parts of the structure for survivors.
One woman told how she had fought her way out of her home in one of the collapsed blocks.

“I used a hammer to break the door of my home which was twisted and locked, and managed to climb out,” she told local channel SET TV, weeping as she spoke.

Men in camouflage uniforms, apparently military personnel, marched into one area of collapse carrying large shovels.

Aerial images of at least two different buildings showed what appeared to be significant devastation. It was unclear if both were residential structures.

The Taiwanese news website ET Today reported a mother and a daughter were among the 34 people pulled from one of the Wei Guan buildings and that the girl drank her urine while waiting for rescue, which came sooner than expected.

The temblor struck about 4am local time. It was located some 36km southeast of Yujing, and struck about 10km underground, according to the US Geological Survey.

It was felt as a lengthy, rolling shake in the capital, Taipei, on the other side of the island. But Taipei was quiet, with no sense of emergency or obvious damage just before dawn.

Officials said there were 256 people registered as living in the complex, which contained 96 apartments.

Dazed and exhausted residents stood outside the toppled buildings, watching rescue workers free survivors — from infants to the elderly, some strapped to stretchers — and carefully hand them down ladders.

Cranes towered over the disaster zone with diggers trying to move slabs of concrete.

Eight shelters have been set up around the city, with over 100 people taking refuge there, while restaurants and hotels offered free food and rooms to residents.

“The buildings collapsed, but Tainan will stand again! Please treat here like your temporary home, rest well and freshen up. You aren’t alone,” said one Tainan hotel called Adagio Travel on its Facebook page.

Separately, at least 30 people were earlier freed from another residential seven-storey tower.

Officials said several blocks had collapsed or half collapsed in other parts of the city, with some buildings left leaning at alarming angles.

Across Tainan, more than 400 people were injured, with over 60 hospitalised. Around 400,000 had been left without water, authorities said, and more than 2,000 homes are still without electricity.

China has offered rescue assistance if needed, according to state news agency Xinhua.

The quake struck at a depth of 10 kilometres (six miles) at around 4:00am (2000 GMT Friday), 39 kilometres northeast of Kaohsiung, Taiwan’s second-largest city.
Taiwan lies near the junction of two tectonic plates and is regularly hit by earthquakes.

The Pacific Tsunami Warning Center said a destructive Pacific-wide tsunami was not expected.

A strong 6.3-magnitude quake which hit central Taiwan in June 2013 killed four people and caused widespread landslides.

A 7.6-magnitude quake struck the island in September 1999 and killed around 2400 people.

Research May Explain Mysterious Deep Earthquakes In Subduction Zones

Geologists from Brown University may have finally explained what triggers certain earthquakes that occur deep beneath the Earth’s surface in subduction zones, regions where one tectonic plate slides beneath another.

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Subduction zones are some of the most seismically active areas on earth. Earthquakes in these spots that occur close to the surface can be devastating, like the one that struck Japan in 2011 triggering the Fukushima nuclear disaster. But quakes also occur commonly in the subducting crust as it pushes deep below the surface — at depths between 70 and 300 kilometers. These quakes, known as intermediate depth earthquakes, tend to be less damaging, but can still rattle buildings.

Intermediate depth quakes have long been something of a mystery to geologists.

“They’re enigmatic because the pressures are so high at that depth that the normal process of frictional sliding associated with earthquakes is inhibited,” said Greg Hirth, professor of earth, environmental, and planetary sciences at Brown. “The forces required to get things to slip just aren’t there.”

But through a series of lab experiments, Hirth and postdoctoral researcher Keishi Okazaki have shown that as water escapes from a mineral called lawsonite at high temperatures and pressures, the mineral becomes prone to the kind of brittle failure required to trigger an earthquake.

“Keishi’s experiments were basically the first tests at conditions appropriate for where these earthquakes actually happen in the earth,” Hirth said. “They’re really the first to show strong evidence for this dehydration embrittlement.”

The work will be published on February 4, 2016 in the journal Nature.

The experiments were done in what’s known as a Grigg’s apparatus. Okazaki placed samples of lawsonite in a cylinder and heated it up through the range of temperatures where water becomes unstable in lawsonite at high pressures. A piston then increased the pressure until the mineral began to deform. A tiny seismometer fixed to the apparatus detected sudden cracking in the lawsonite, a signal consistent with brittle failure.

Okazaki performed similar experiments using a different mineral, antigorite, which had been previously implicated as contributing to intermediate depth seismicity. In contrast to lawsonite, the antigorite failed more gradually — squishing rather than cracking — suggesting that antigorite does not play a role in these quakes.

“That’s one of the cool things about this,” Hirth said. “For 50 years everyone has assumed this is a process related to antigorite, despite the fact that there wasn’t much evidence for it. Now we have good experimental evidence of this dehydration process involving lawsonite.”

If lawsonite is indeed responsible for intermediate depth earthquakes, it would explain why such quakes are common in some subduction zones and not others. The formation of lawsonite requires high pressures and low temperatures. It is found in so-called “cold” subduction zones in which the suducting crust is older and therefore cooler in temperature. One such cold zone is found in northwest Japan. But conditions in “hot” subduction zones, like the Cascadia subduction zone off the coast of Washington state, aren’t conducive to the formation of lawsonite.

“In hot subduction zones, we have very few earthquakes in the subducting crust because we have no lawsonite,” Okazaki said. “But in cold subduction zones, we have lawsonite and we get these earthquakes.”

Ultimately, Hirth says research like this might help scientists to better understand why earthquakes happen at different places under different conditions.

“Trying to put into the context of all earthquakes how these processes are working might be important not just for understanding these strange types of earthquakes, but all earthquakes,” he said. “We don’t really understand a lot of the earthquake cycle. Predictability is the ultimate goal, but we’re still at the stage of thinking about what’s the recipe for different kinds of earthquakes. This appears to be one of those recipes.”