Sioux Falls Scientists endorse Earthquake! for showing how scientists are
struggling to predict earthquakes. It's not easy and the clues are few.
Earthquake! (2007) - 56 minutes
Earthquake! at Amazon.com
"Only fools, charlatans and liars predict earthquakes."
So quipped the late Charles Richter, who knew enough about nature's ultimate upheavals to invent the scale by which they are measured.
Nevertheless, prediction is the siren song of earthquake studies - the alluring problem on which reputations can be won or wrecked. Not just careers, but millions of lives and billions of dollars depend on the ability of scientists to say just when and where the earth will move. In fact, much of the entire history of earth science has been a struggle to account for the periodic lurching of solid ground. Follow as Nova takes a look at the high-stakes quest to predict earthquakes.
2-4-19 Seismic boom may explain why 2018 Palu earthquake was so devastating
More than 2000 people died when an earthquake in Indonesia triggered a tsunami last year. We now have a better idea of why the event was so devastating — Earth’s crust ruptured so quickly that it effectively broke the sound barrier for earthquakes and generated a seismic boom. An earthquake occurs when stress built up in Earth’s crust literally reaches breaking point, which causes the rock to rupture producing a fault in the crust. The crack begins close to the earthquake’s epicentre and then spreads for potentially hundreds of kilometres, like a tear spreading through a sheet of paper as the two halves are pulled apart. As the rock ruptures, it sends out shock waves – called shear waves – that radiate out through the crust at around 3.5 kilometres per second. It’s these shock waves that shake the ground and cause the damage and destruction. But during the Palu earthquake that struck Sulawesi on 28 September 2018, those shock waves seem to have been made even more intense. Two independent teams of geologists have analysed geological data from the quake and think they know why. The earthquake ruptured the crust on a fault that is roughly 180 kilometres long, and the movement spread along that fault at a speed of 4.1 kilometres per second. This means the fault ruptured along its length at a faster speed than the shock waves it generated. The simplest way to understand what that means in practice is to think of a supersonic jet plane. As the aircraft accelerates it eventually travels faster than the soundwaves its engines generate. As it breaks this sound barrier, the jet creates a sonic boom that contains an enormous amount of energy.
3-27-18 Powerful New England quake recorded in pond mud
The layers of a sediment core show a change around the time of the 1755 Cape Ann earthquake. The history of New England’s most damaging earthquake is written in the mud beneath a Massachusetts pond. Researchers identified the first sedimentary evidence of the Cape Ann earthquake, which in 1755 shook the East Coast from Nova Scotia to South Carolina. The quake, estimated to have been at least magnitude 5.9, took no lives but damaged hundreds of buildings. Within a mud core retrieved from the bottom of Sluice Pond in Lynn, Mass., a light brown layer of sediment stands out amid darker layers of organic-rich sediment, the researchers report March 27 in Seismological Research Letters. The 2-centimeter-thick layer contains tiny fossils usually found near the shore, as well as types of pollen different from those found in the rest of the core. Using previous studies of the pond’s deposition rates, geologist Katrin Monecke of Wellesley College in Massachusetts and her colleagues determined the layer dates to between 1740 and 1810. That light-brown layer is likely a turbidite, sediment jumbled up by a sudden lake slope failure, the study says. There are no other turbidites in the core, which spans about 400 years, suggesting the slopes held fast through floods and hurricanes. But the Cape Ann quake was likely a strong enough trigger to cause the slope failure. Though the eastern United States is not at the seismically active edge of a tectonic plate, it has occasionally had its ground-shakers (SN Online: 8/23/11). The study suggests other East Coast lakes and ponds may contain evidence of prehistoric quakes, giving researchers a new way to estimate their frequency.
3-24-18 How effective are earthquake early warning systems?
Earthquake early warning detection is more effective for minor quakes than major ones. This is according to a new study from the United States Geological Survey. Seismologists modelled ground shaking along California's San Andreas Fault, where an earthquake of magnitude 6.5 or more is expected within 30 years. They found that warning time could be increased for residents if they were willing to tolerate a number of "false alarms" for smaller events. This would mean issuing alerts early in an earthquake's lifespan, before its full magnitude is determined. Those living far from the epicentre would occasionally receive warnings for ground shaking they could not feel. "We can get [greater] warning times for weak ground motion levels, but we can't get long warning times for strong shaking," Sarah Minson, lead author of the study, told BBC News. "Alternatively, we could warn you every time there was an earthquake that might produce weak ground shaking at your location... A lot of baby earthquakes don't grow up to become big earthquakes," she added. Earthquake early warning systems have been in place in Mexico and Japan for years. Now, a system called ShakeAlert is being developed for the west coast of North America. So how can it predict the unpredictable? In short, it can't. "It's a misnomer... because it's not earthquake early warning, the earthquake has already happened... It's ground motion early warning," said Dr Minson. Earthquakes occur along tectonic plate boundaries and faults in the Earth's crust - long fractures where friction has built up over time.
3-21-18 False alarms may be a necessary part of earthquake early warnings
Alerts would have to go out before the temblor’s strength is clear. Earthquake warning systems face a tough trade-off: To give enough time to take cover or shut down emergency systems, alerts may need to go out before it’s clear how strong the quake will be. And that raises the risk of false alarms, undermining confidence in any warning system. A new study aims to quantify the best-case scenario for warning time from a hypothetical earthquake early warning system. The result? There is no magic formula for deciding when to issue an alert, the researchers report online March 21 in Science Advances. “We have a choice when issuing earthquake warnings,” says study leader Sarah Minson, a seismologist at the U.S. Geological Survey, or USGS, in Menlo Park, Calif. “You have to think about your relative risk appetite: What is the cost of taking action versus the cost of the damage you’re trying to prevent?” For locations far from a large quake’s origin, waiting for clear signs of risk before sending an alert may mean waiting too long for people to be able to take protective action. But for those tasked with managing critical infrastructure, such as airports, trains or nuclear power plants, an early warning even if false may be preferable to an alert coming too late (SN: 4/19/14, p. 16).
2-17-18 California is long overdue for a major earthquake
Is there anything the state can do to prepare? California earthquakes are a geologic inevitability. The state straddles the North American and Pacific tectonic plates and is crisscrossed by the San Andreas and other active fault systems. The magnitude 7.9 earthquake that struck off Alaska's Kodiak Island on Jan. 23, 2018 was just the latest reminder of major seismic activity along the Pacific Rim. Tragic quakes that occurred in 2017 near the Iran-Iraq border and in central Mexico, with magnitudes of 7.3 and 7.1, respectively, are well within the range of earthquake sizes that have a high likelihood of occurring in highly populated parts of California during the next few decades. The earthquake situation in California is actually more dire than people who aren't seismologists like myself may realize. Although many Californians can recount experiencing an earthquake, most have never personally experienced a strong one. For major events, with magnitudes of 7 or greater, California is actually in an earthquake drought. Multiple segments of the expansive San Andreas Fault system are now sufficiently stressed to produce large and damaging events. The good news is that earthquake readiness is part of the state's culture, and earthquake science is advancing — including much improved simulations of large quake effects and development of an early warning system for the Pacific coast. California occupies a central place in the history of seismology. The April 18, 1906 San Francisco earthquake (magnitude 7.8) was pivotal to both earthquake hazard awareness and the development of earthquake science — including the fundamental insight that earthquakes arise from faults that abruptly rupture and slip. The San Andreas Fault slipped by as much as 20 feet (six meters) in this earthquake.
9-27-17 Mexico City quake: A few seconds’ warning can still save lives
Mexico City quake: A few seconds’ warning can still save lives
The recent earthquake in Mexico City shows even the best tremor alarms sometimes only go off seconds before – but clever planning can mean those few seconds save many people. Last week’s magnitude 7.1 earthquake caught me, and everyone else who lives in Mexico City, by surprise. The problem was that everyone here is accustomed to getting plenty of warning before an earthquake – and this time we didn’t. Since 1993, Mexico City has had a fully operational earthquake early warning system. When a magnitude 8.1 quake struck on 8 September, the city got over a minute of warning. But the quake on 19 September showed that the system can’t respond to all types of events. Its failure to warn the city may hold lessons, not just for Mexico, but also for other countries working to give their citizens a head start. “This event in Mexico City is critical,” says Richard Allen at the University of California, Berkeley.
9-21-17 There is no way to spot big earthquakes ahead of time
There is no way to spot big earthquakes ahead of time
Large earthquakes look just like small ones when they start out, so early warning systems have no clues to help figure out if a quake is going to be huge. All earthquakes look the same when they start, making it unlikely we will be able to predict which will cause the most devastation from early observations. Early warning systems rely on seismometers picking up tremors and sounding the alarm for nearby cities before major shaking starts. Even a few seconds’ warning can make a lot of difference, both for individual people and for organisations like hospitals, says Daniel Trugman at the Scripps Institution of Oceanography in La Jolla, California. For example, Mexico’s early warning system gave everyone a 10 to 15 second heads-up before Tuesday’s magnitude 7.1 earthquake, says Men-Andrin Meier at the California Institute of Technology in Pasadena. The trouble is, such warning systems must estimate the size of an earthquake from the earliest seismometer readings. By looking at past earthquakes, Meier had hoped to show that large and small earthquakes started differently, so that the systems could spot the really big ones. “Unfortunately, our results show that such hopes are not realistic,” he says.While quakes occur suddenly, they don’t reach their maximum strength and spread all at once. Instead, they start in a small area and then spread along a plate boundary at several kilometres per second. These movements determine how wide an area is affected, and how badly.
9-20-17 Mexico hit by second huge quake caused by same tectonic strain
Mexico hit by second huge quake caused by same tectonic strain
The country has been struck by its second big earthquake in less than two weeks, causing dozens of buildings to collapse. Mexico has been rocked by its second big earthquake in less than two weeks and could be hit by more. The magnitude 7.1 earthquake struck central Mexico just after 6pm local time on Tuesday. Its epicentre was located 120 kilometres south-east of Mexico City at a depth of 51km. Dozens of buildings in Mexico City collapsed and over 200 people are reported dead. The latest tremor came 11 days after a magnitude 8.1 earthquake occurred off the coast of southern Mexico, killing 98 people. Both quakes were sparked by heightened tension between the Cocos tectonic plate, which borders the western coast of Mexico, and the North American tectonic plate. As the Cocos plate slid underneath its North American neighbour, it fractured in two different places, known as faults. “What happened yesterday was most likely a tearing motion in the subducting Cocos plate,” says David Rothery of the Open University in the UK. The two fractures were several hundred kilometres apart, suggesting the 8 September earthquake did not trigger the 19 September one, says Stephen Hicks at the University of Southampton in the UK. “They were both caused by bending and tension in the Cocos plate, but in different ways. The second earthquake was not an aftershock but a separate quake entirely.” It is unclear why the two tectonic plates are currently clashing so violently. The depth of the subduction zone – where the Cocos plate is thrusting under the North American plate – makes it difficult to assess how the strain is building up, says Hicks.
9-20-17 Mexico: Huge earthquake topples buildings, killing more than 200
Mexico: Huge earthquake topples buildings, killing more than 200
A strong earthquake has struck central Mexico, killing more than 200 people and toppling dozens of buildings in the capital, Mexico City. At least 30 people, mostly children, died after a school collapsed in the capital, local media report. The 7.1 magnitude quake also caused major damage in neighbouring states. It struck shortly after many people had taken part in an earthquake drill, exactly 32 years after a quake killed thousands in Mexico City. The country is prone to earthquakes and earlier this month an 8.1 magnitude tremor in the south left at least 90 people dead. Though it struck a similar region, Tuesday's earthquake does not appear to be connected with the quake on 7 September, which was at least 30 times more energetic, the BBC's Jonathan Amos writes. The epicentre of the latest quake was near Atencingo in Puebla state, about 120km (75 miles) from Mexico City, with a depth of 51km, the US Geological Survey says. The prolonged tremor hit at 13:14 local time (18:14 GMT) on Tuesday and sent thousands of residents into the streets.
9-13-17 Mysterious lights in the sky seen after Mexico’s huge earthquake
Mysterious lights in the sky seen after Mexico’s huge earthquake
Magnitude isn’t the only demonstration of an earthquake’s power. For centuries, mysterious lights have popped up in the wake of strong quakes. Mysterious lights in the sky seen after Mexico’s huge earthquakeAfter an 8.1-magnitude earthquake struck off the southern coast of Mexico on 7 September, videos of fuzzy green smears in the night sky went viral online. Earthquake lights are a phenomenon so unusual that they border on myth. The first known reports of them are from 89 BC, with spotty descriptions over the centuries. Recently, they’ve been seen during foreshocks and the main earthquake in L’Aquila, Italy, in 2009, and as flashes of blue lightning over Wellington, New Zealand, in 2016. “These phenomena are well-documented because of so many security cameras running day and night now,” says Friedemann Freund at NASA’s Ames Research Center. Earthquake lights are electric discharges that come out of the ground and can rise up to 200 metres in the air, says Freund. Lights are sometimes observed in the days and hours leading up to an earthquake, and at other times during or after it. But how they work is still mysterious. Part of the challenge in getting to the bottom of this is that earthquake lights have been described in so many ways: as glowing globes, flickering flames from the ground, or even branching lightning that sparks from Earth instead of the sky. And in many instances, they could be explained by other phenomena, such as volcanic flames from fissures, streaking fireball meteors or auroras.
9-8-17 Mexico on tsunami alert after biggest earthquake in 85 years
Mexico on tsunami alert after biggest earthquake in 85 years
The US Geological Survey reported the earthquake's magnitude as 8.1, making it the biggest earthquake in Mexico since 1932. A major earthquake off Mexico’s southern coast has killed at least five people, sparking tsunami warnings. Further dangerous aftershocks are also expected. The US Geological Survey reported the earthquake’s magnitude as 8.1, making it the biggest earthquake in Mexico since 1932. The USGS said the quake struck at 11.49pm local time on Thursday and its epicentre was 165 kilometres west of Tapachula in Chiapas, not far from Guatemala. It had a depth of 69.7 kilometres. The quake was so strong that it caused buildings to sway violently in Mexico’s capital, more than 1,000 kilometres away. Houses toppled and the quake produced tsunami waves and sent people running into the streets in panic. President Enrique Pena Nieto said 62 aftershocks followed the quake and it was possible one as strong as 7.2 could hit in the next 24 hours. “The house moved like chewing gum and the light and internet went out momentarily,” said resident Rodrigo Soberanes, who lives near San Cristobal de las Casas in Chiapas. Chiapas Governor Manuel Velasco said three people were killed in San Cristobal, including two women who died when a house and a wall collapsed. He urged people living near the coast to leave their homes as a protective measure. “There is damage to hospitals that have lost energy,” he said. “Homes, schools and hospitals have been damaged.”
9-8-17 Mexico's strongest quake in century strikes off southern coast
Mexico's strongest quake in century strikes off southern coast
An earthquake described by Mexico's president as the country's strongest in a century has struck off the southern coast, killing at least 33 people. The quake, which President Enrique Peña Nieto said measured 8.2, struck in the Pacific, about 87km (54 miles) south-west of Pijijiapan. Severe damage has been reported in Oaxaca and Chiapas states. A tsunami warning was initially issued for Mexico and other nearby countries, but later lifted. The quake, which struck at 23:50 local time on Thursday (04:50 GMT Friday), was felt hundreds of miles away in Mexico City, with buildings swaying and people running into the street. The tremors there were reported to have lasted up to a minute. President Peña Nieto said some 50 million Mexicans would have felt the tremor and that the death toll might rise. Twenty-three people are reported dead in Mexico's Oaxaca state, 17 of them in the town of Juchitán, state Governor Alejandro Murat said. Another seven people were reported killed in Chiapas and two children died in Tabasco state, one a baby who died when power was cut to a respirator. At least one person was killed in Guatemala, its president has said. Social media images showed collapsed buildings in Oaxaca, including in the city of the same name, and in Juchitán, where the municipal palace and a number of other structures were levelled.
5-26-17 Nowcasting may help forecast big earthquakes in 53 major cities
Nowcasting may help forecast big earthquakes in 53 major cities
Records of small quakes can help us gauge how close we are to really big ones, using a technique borrowed from economics and finance. The ground can start shaking under your feet with almost no warning. Earthquakes have proven nearly impossible to forecast so far, but a technique borrowed from economics and finance can now help us estimate how high the risk is. Seismic nowcasting, as it is called, assesses the current risk of a major earthquake in a given area based on the smaller tremors the area has experienced in the past. Nowcasting gives a snapshot in time, whereas forecasting looks into the future. It’s akin to metrics that incorporate the latest fluctuating data to evaluate whether there’s a looming downturn in an economy or industry. John Rundle at the University of California, Davis, and colleagues have used the technique on data from the US Geological Survey’s earthquake catalogue to calculate the “earthquake score” of 53 major cities around the world. “If you have a high earthquake score, and then you start seeing more small earthquakes, I’d get worried. You’re accumulating hazard, so to speak,” says Rundle, who presented the team’s results at an earth science conference in Chiba, Japan, on 22 May. Geological fault systems on the margins of tectonic plates can evolve rapidly, and the researchers worked on the assumption that earthquakes occur over irregular cycles. They also assumed that some patterns are regular, though, with an average number of small earthquakes striking a region between the rarer “big ones”, which are tens of thousands of times more earth-shattering. This allows the researchers to figure out what stage in a cycle a given city has reached based on how many small quakes have hit since the last big one. Stresses and strain build up over time with each new small earthquake – a small quake being one between magnitudes 3.0 and 6.5. Eventually the rock cannot tolerate the stress, and an earthquake releases energy while fracturing the rock. If a lot of stress has built up, then the quake could be a big one.
12-14-16 Sentinels map Earth's slow surface warping
Sentinels map Earth's slow surface warping
British researchers are now routinely mapping a great swathe of Earth's surface, looking for the subtle warping that ultimately leads to quakes. The team is processing satellite images to show how rocks in a belt that stretches from Europe's Alps to China are slowly accumulating strain. Movements on the scale of just millimetres per year are being sought. The new maps are being made available to help researchers produce more robust assessments of seismic hazard. The kind of change they are trying to chart is not noticeable in the everyday human sense, but over time will put faults under such pressure that they eventually rupture - often with catastrophic consequences. "We may well discover regions that have very small strain rates that we have not been able to detect before," said Dr Richard Walters "And that may well tell us that earthquakes are more likely in some areas that traditionally have been thought of as being completely stable and not at risk of having earthquakes at all."
Sioux Falls Scientists endorse Earthquake! for showing how scientists are
struggling to predict earthquakes. It's not easy and the clues are few.