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Home / Science / Oil has put LA on the map, but potentially increased national earthquake risk

Oil has put LA on the map, but potentially increased national earthquake risk



Hoping to escape traffic on the way home from Los Angeles International Airport, Susan Hough drove La Cienega Boulevard through the heart of Inglewood Oil Field. It was a terrible scene. Countless black Pump Jacks nodded in the scrubby hills like a herd of mechanical giraffes.

A hundred years ago this would have been a common sight. Rows of derrick wreaths used to stand on the beaches of Huntington and Venice. The spindly towers thronged Signal Hill and flanked the tar pits of La Brea.

But Hough, a geophysicist from the US Geological Survey in Pasadena, says there may have been another consequence of this pumping. Their research suggests that it may have caused almost all moderate earthquakes that shook the Los Angeles Basin in the first half of the 20th century, previously attributed to geological forces.

If this is the case, this could be good news the region.

"The LA Basin could generally be safer for natural earthquakes than we thought," Hough said.

Hough has been looking for years for possible connections between oil production and seismicity. She and her colleagues have analyzed historical damage reports to determine the exact locations of earthquakes that occurred prior to the commencement of high-quality seismic surveillance in the 1

950s. They also thought about oil extraction data for the Los Angeles area to calculate how pumping would have affected local disturbances.

Again and again the researchers found suspicious compounds.

"The earthquakes are darts and they are pretty close to the bulls' eyes, where stress has changed," said Hough, whose latest study on the subject was published in the Journal of Geophysical Research late last year.

The idea is controversial: it is difficult to pin down the exact cause of an earthquake, especially one that occurred so long ago, and as scientists often say, correlation is not a cause.

But Jenny Suckale, a geophysicist at the University of California Stanford University said Hough and her colleagues did some good detective work.

"They really tried to pull the pieces together," said Suckale, who was not involved in the research, "it seems obvious, but it will not often done – not at this stage of completion. "

Man-made earthquakes have shaken states like Oklahoma and Texas in recent years Hough wondered if something similar had happened during the oil boom of L. A. in the first decades of the twentieth century.

At that time there were no seismometers, but there were many people who felt the earthquakes. After a quake, the postmasters distributed questionnaires to residents, asking if the shaking could shake or overturn their porcelain. Newspapers reported where the worst damage had occurred.

Decades later, this information allowed researchers to estimate the strength and location of historical earthquakes. And in 2016, Hough and her USGS colleague Morgan Page published a study suggesting that oil exploration could have caused many of L.A.'s earthquakes in the early 20th century. The earthquakes took place near oil fields and agreed with the activity changes there, the researchers noted.

A magnitude 5 quake in 1920, which toppled chimneys and brick facades in Inglewood, took place shortly after the discovery of natural gas at A instead of local oil field. Another earthquake shook Whittier in 1929, when homes at the nearby Santa Fe Springs oil field had increased.

By far the most significant was the Long Beach earthquake of 1933. At the magnitude 6.4 earthquake, at least 120 people were killed; Destroyed homes, churches, and schools, as well as damaged buildings within 50 km of downtown Los Angeles. It took about six months after Superior Oil Co. drilled off Huntington Beach into a 4,000-foot-deep deposit.

Hough said the two events were connected, but could not be said with certainty. "We have only a spatial and temporal connection," she said.

Soon after the Long Beach earthquake, scientists completed the first network of seismometers in Los Angeles. As the war effort sparked another oil boom in the late 1930s and early 1940s, the devices registered eight more moderate earthquakes.

The researchers could then use seismic data to locate the epicenter, but Hough said the results were not very reliable and often conflicted where people reported the strongest tremors.

She and Roger Bilham, a University of Colorado seismologist, consulted newspapers and shaking reports to refine the locations of these events. Some returned less than 5 miles.

After the records were corrected, the researchers found that all earthquakes were near active oilfields. And when Hough and Bilham were included in the data of the oil industry, they saw that quakes occurred after an increase in production or deepening of wells.

For example, a 4.5 magnitude quake shook the harbor shortly after Christmas 1939, stopping the clocks and a deep, roaring noise that unsettled the Malibu residents. It hit shortly after winning oil production in Wilmington, one of the largest in the region.

In the autumn of 1941, a quake occurred near the Dominguez oil field, where recently a new source had hit the oil a mile and a quarter below the surface.

"In these earthquakes, you keep seeing the same story," Hough said.

The researchers also modeled how pumping would have changed the load on local faults. They had begun to hit rocks in the depths of the earthquakes in 1940, they found.

It's not proof, but the calculations support the argument that oil production in the LA Basin could cause earthquakes, Gillian Foulger said. a geophysicist at Durham University in the UK who was not involved in the study.

"You have done an extremely impressive job," she said.

When these quakes were caused by oil production, they were for other reasons than Oklahoma, Hough said. The culprit seems to be the large quantities of oil and gas effluents that are injected deep into the soil. As a result, the pore pressure can be increased in case of errors, which facilitates slipping.

Oil production was designed to reduce pore pressure, reducing the risk of an earthquake. But it can have other consequences.

"If you suck oil from a reservoir," Bilham said, "what you actually do is remove the support for all the rocks about it." This can cause sinking – and trembling

This is a phenomenon that scientists have noticed at oil and gas production sites around the world, Suckale said. In the Netherlands, protests over an eruption of induced earthquakes led the government to announce the closure of a huge natural gas field.

The same thing may have happened in Los Angeles.

Consider the Wilmington oil field, where pumping generated a mile-wide depression. It nearly swallowed up the southern California Edison power plant on Terminal Island, kinking the railway lines leading into the harbor. As the problem worsened, the Navy warned that if the oil production did not slow down, it would have to close its increasingly muddy yard. By 1958, some areas had dropped more than 25 feet.

Finally, business leaders came up with a solution.

The oil companies began to inject water underground to counteract the subsidence and boost oil production in depleted wells. Water floods, as the practice became known, soon became the standard.

The Los Angeles Basin has been less earthquake-prone since the middle of the last century, though the district still produces 23 million barrels of oil per year. Hough said it was no coincidence.

Water floods could have stabilized the burden of errors, she said. Or by recovering all of this oil, the errors could eventually be closed due to a reduced pore pressure.

However, the studies of Hough and others suggest that in the last 100 years there have not been many other significant earthquakes that did not give some a cumbersome connection to oil, she said.

Hough knows that her ideas are controversial. "Induced earthquakes have long been something of a third tool in seismology," she said.

Their findings contradict a study conducted in 2015 by Caltech seismologist Egill Hauksson, which found no clear link between oil production and earthquakes in LA's past. This analysis covered 80 years from 1935 to 2014, a time in which drilling techniques have changed dramatically. And the Hauksson team used the original sites for historic earthquakes.

John Vidale, a USC seismologist and director of the Southern California Earthquake Center, said the different conclusions may also reflect the willingness of researchers to go limb.

"Sue likes to make speculative claims," ​​he said. "And most of them have been holding."

Vidale agrees that this is plausible. It is not the only possible explanation for the accumulation of seismic events of the 20th century, he said, but "the connection of the earthquakes with oil withdrawals seems reasonable and at least halfway convincing."

If Hough and her colleagues are right, the Los Angeles basin may be less seismically active than scientists thought.

"It would lower the rate at which we expect big earthquakes," Vidale said.

[EDITORS: STORY CAN END HERE]

Clear as 6.7 The 1994 Northridge earthquake has shown that the Greater Los Angeles area is exposed to very real seismic risks. The crisscrossing of the city continues, meaning that they are a threat regardless of the earthquakes of the past, Hauksson said.

One thing is certain, though: the early earthquakes – especially the Long Beach event of 1933 – kept Californians alert to the dangers under their feet. Even if the disaster was caused by oil drilling, it catalyzed efforts to impose tighter building regulations and other seismic safety measures.

"Especially this earthquake has made everything safer to move forward," said Hough.

PHOTOS (help) with pictures, contact 312-222-4194): LA-OIL-EARTHQUAKES


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