Tag Archives: earthquakes

Big earthquake in South Korea linked to geothermal power plant

South Korea’s second largest earthquake has now been linked by two different studies to the injection of water deep below the surface at a new geothermal power plant.

Perched on South Korea’s southeast coast and far from grinding tectonic plates, Pohang is an unlikely spot for a big earthquake. Before the geothermal plant’s two wells were drilled, there had never been an earthquake there of any significance, says Kwanghee Kim, a seismologist at Pusan National University in Busan, South Korea, and lead author of one study. But while Kim was monitoring the aftermath of an unrelated earthquake in 2016, he began to detect rumbles from Pohang. That prompted his lab to deploy eight temporary seismic sensors at the site, which were finally in place on 10 November 2017. He expected any quakes to be small—after all, the largest previous quake tied to enhanced geothermal power, in Basel, Switzerland, was just 3.4 in magnitude.

It took only 5 days to be proved wrong. “The Pohang earthquake was larger than any predicted by existing theories,” Kim says. Although some initial measures placed the source of the quake several kilometers away from the plant, Kim’s network revealed that the earthquake, and several of its foreshocks, all began right below the 4-kilometer-deep well used to inject water into the subsurface to create the plant’s heating reservoir. Indeed, it appears likely that the well’s high-pressure water lubricated an unknown fault in the rock, causing it to slip and triggering the quake, Kim says.

A second paper, by European scientists who used regional seismic data, reinforces the South Korean team’s results, in particular its shallow depth. That study also points out that an earlier 3.1-magnitude earthquake also took place near the well bottom, increasing the odds of a common source. Satellite measures of shifts in the surface after the November 2017 quake support that idea, says Stefan Wiemer, the second study’s lead author and director of the Swiss Seismological Service in Zurich. It’s clear the locked fault was storing energy that was waiting to be released, Wiemer says. “If that fault would have gone next Tuesday or 50 years from now, we’ll never know.”

The article notes that scientists had previously concluded that injecting water underground for geothermal purposes was okay (since it reduced use of fossil fuels) while doing the same for fracking (to obtain and use fossil fuels) was bad.. The data here actually suggests just the reverse, since fracking has never produced an earthquake as large as the 5.5 magnitude Pohang quake.

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Database of presumed human-caused earthquakes created

The uncertainty of science: Geologists have assembled a database of more than 700 earthquakes they think might have been caused by human activity.

The Human-Induced Earthquake Database, or HiQuake, contains 728 examples of earthquakes (or sequences of earthquakes) that may have been set off by humans over the past 149 years. Most of them were small, between magnitudes 3 and 4. But the list also includes several large, destructive earthquakes, such as the magnitude-7.8 quake in Nepal in April 2015, which one paper linked to groundwater pumping.

Miles Wilson, a hydrogeologist at Durham University, UK, and his colleagues describe the database in a paper set to be published on October 4 in Seismological Research Letters2. The scientists say that HiQuake is the biggest, most up-to-date public listing of human-caused quakes ever made. By bringing the data together in this way, they hope to highlight how diverse induced quakes can be — and help society to understand and manage the future risk.

Many of these quakes were likely caused by human activity. Many however might not have been. The jury is still out, as the article reluctantly admits near the end.

All possible instances of induced quakes were included “without regard to plausibility”, writes the team, because of the difficulty involved in deciding what constitutes absolute proof that an earthquake was caused by human activity. But that could mislead people about the real hazard from induced quakes, says Raphaël Grandin, a geophysicist at the Institute of Earth Physics in Paris. “When you put a dot in the database, and a scientific reference behind it, then you may lead the non-expert to think that the earthquake was caused by humans,” he says. Such a listing might hide scientific uncertainty, as with the Chinese quake: despite the paper linking it to reservoir filling, many seismologists do not believe it was triggered by human activity.

In other words, they included every quake that had the slightest suggestion it was connected to human activity, without noting the uncertainties. This makes this database to me somewhat suspect. Rather than identify the known reliable links between human activity and quakes in order to learn what causes them, this database seems more designed as a political propaganda tool aimed at limiting future human activity. It certainly doesn’t clarify our knowledge on this subject, but instead muddies the water significantly.

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Largest quake in Yellowstone since 2014

The USGS today recorded a magnitude 4.5 earthquake at Yellowstone today, the largest since a magnitude 4.8 occurred in March 2014, and part of a continuing swarming of small quakes that began on June 12.

This sequence has included approximately thirty earthquakes of magnitude 2 and larger and four earthquakes of magnitude 3 and larger, including today’s magnitude 4.5 event.

It is hard to say whether this swarm of small quakes portend a really big volcanic event, or will simply die off in the coming days. Recent data at Yellowstone has suggested the former is possible, though not imminent.

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Statistical analysis suggests Moon can cause quakes

The uncertainty of science: A careful statistical analysis of when major earthquakes occur has suggested they are more likely to be more powerful if they occur around the full and new moons when tidal forces are at their peak.

Satoshi Ide, a seismologist at the University of Tokyo, and his colleagues investigated three separate earthquake records covering Japan, California and the entire globe. For the 15 days leading up to each quake, the scientists assigned a number representing the relative tidal stress on that day, with 15 representing the highest. They found that large quakes such as those that hit Chile and Tohoku-Oki occurred near the time of maximum tidal strain — or during new and full moons when the Sun, Moon and Earth align.

For more than 10,000 earthquakes of around magnitude 5.5, the researchers found, an earthquake that began during a time of high tidal stress was more likely to grow to magnitude 8 or above.

As these results are based entirely on statistical evidence, not on any direct link between tidal forces and actual quakes, they are quite uncertain and unproven.

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Italian appeals court overturns convictions of earthquake scientists

An Italian appeals court on Monday overturned the manslaughter convictions of six Italian earthquake scientist for the deaths of over 300 people during the L’Aquila earthquake of 2009.

Only one of the seven experts originally found guilty was convicted today: Bernardo De Bernardinis, who in 2009 was deputy head of Italy’s Civil Protection Department and who will now serve 2 years in jail, pending any further appeals.

De Bernardinis had been the guy who had publicly said that the swarm of tremors prior to the quake had released energy and thus reduced the chance of an earthquake, a claim that geology scientists do not support.

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Scientists struggle with earthquake data in the Pacific northwest

The uncertainty of science: A second look at cores drilled in the Pacific northwest has raised doubts about the previous conclusions that the region faces the threat of megaquakes every few centuries.

The bottom line is that though geologists are very confident the northwest faces the threat of future quakes, they can’t yet predict with any confidence their rate or intensity.

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Geologists have determined that the magma reservoir under Yellowstone is much bigger than previously thought.

The uncertainty of science: Geologists have determined that the magma reservoir under Yellowstone is much bigger than previously thought.

Jamie Farrell, a postdoctoral researcher at the University of Utah, mapped the underlying magma reservoir by analysing data from more than 4,500 earthquakes. Seismic waves travel more slowly through molten rock than through solid rock, and seismometers can detect those changes.

The images show that the reservoir resembles a 4,000-cubic-kilometre underground sponge, with 6–8% of it filled with molten rock. It underlies most of the Yellowstone caldera and extends a little beyond it to the northeast.

The geologists also noted that the threat from a huge volcanic eruption is less of a concern than that of earthquakes.

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The trial of seven earthquake scientists in Italy on charges of manslaughter for not correctly predicting the earthquake in L’Aquila continued yesterday with each of the defendants testifying.

The trial of seven earthquake scientists in Italy on charges of manslaughter for not correctly predicting the earthquake in L’Aquila continued yesterday with each of the defendants testifying.

The trial will not resume again until the fall.

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A big sideways slip on Mars

Mars Reconnaissance Orbiter today released an image of a really spectacular transform fault on Mars, a spot where the ground cracked and two sections moved sideways to each other. In this case, the sideways movement was about 300 feet. The image is posted below the fold.

Compare that with the Japanese magnitude 9 earthquake on March 11, which only shifted the seabed sideways 165 feet while raising it 33 feet. The quake that moved these two pieces of Martian bedrock sideways must have been quite a ride.
» Read more

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The trial of seven Italian earthquake experts facing manslaughter charges for not correctly predicting an earthquake continued this week.

The trial of seven Italian earthquake experts facing manslaughter charges for not correctly predicting a deadly earthquake continued this week.

The prosecution’s argument that the experts had underplayed the possible occurrence of a major quake was bolstered by testimony from Daniela Stati, the former civil protection officer for Abruzzo, who took an active role in the March 31 meeting. Stati confirmed what she had previously told prosecutors in 2010, that one of the indicted said during the meeting that the continuing tremors represented a “favorable signal” because there was a continuous discharge of energy that made stronger tremors less likely. In fact, scientific evidence suggests that groups of small earthquakes tend instead to increase the chances of a major earthquake nearby, even though the absolute probability of such a quake remains low. Stati said that nobody within the commission objected to this statement. She also underlined that the “reassuring message” given to the press by her, L’Aquila Mayor Massimo Cialente, and two of the indicted, Franco Barberi and Bernardo De Bernardinis, was based on comments made at the meeting.

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The strange rubbing boulders of Chile

The strange rubbing boulders of Chile.

Then, on another trip to the Atacama, Quade was standing on one of these boulders, pondering their histories when a 5.3 magnitude earthquake struck. The whole landscape started moving and the sound of the grinding of rocks was loud and clear.

“It was this tremendous sound, like the chattering of thousands of little hammers,” Quade said. He’d probably have made a lot more observations about the minute-long event, except he was a bit preoccupied by the boulder he was standing on, which he had to ride like a surfboard. “The one I was on rolled like a top and bounced off another boulder. I was afraid I would fall off and get crushed.”

The abstract is here.

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