Morocco was shaken Friday night by a massive magnitude 6.8 earthquake, the country’s worst seismic in at least 120 years. More least 2,100 people have perished, according to officials, and the death toll is expected to grow when rescuers reach distant, mountainous areas affected by the disaster.
According to the US Geological Survey, the Mediterranean region is seismically active, however such severe earthquakes are uncommon in North Africa. The latest earthquake in Morocco was caused by a phenomenon known as a “reverse fault,” in which tectonic plates slowly collide, causing the Earth’s crust to thicken. The stress from the collision is then released abruptly in the form of an earthquake.
Because earthquakes are rare in the area, few structures are built to withstand them, and locals have limited experience responding when one occurs. Many of Morocco’s centuries-old structures were severely damaged.
However, earthquakes can still be fatal in earthquake-prone areas. A massive magnitude 7.8 earthquake shook Turkey and Syria early Monday morning in February. A 7.7 magnitude earthquake struck the area a few hours later. The quakes killed over 50,000 people and destroyed over 6,600 buildings in the region.
Two significant fault lines cross Turkey on a regular basis, causing shocks. Larger earthquakes are less common, but nevertheless occur on a regular basis. A magnitude 5.9 earthquake struck Turkey last November. In 2020, a magnitude 7.0 earthquake shook the Aegean Sea between Turkey and Greece.
While scientists have greatly improved their understanding of where earthquakes are likely to occur, forecasting when they will occur remains impossible. The rumbling earth can easily take people off guard, exacerbating the death and destruction that follows.
In light of the recent events, here’s a primer on earthquakes, as well as some of the most recent research on measuring and predicting them.
1) What are the causes of earthquakes?
When enormous slabs of the earth’s crust suddenly move past each other, an earthquake occurs. These pieces, known as tectonic plates, sit on top of the earth’s mantle, a layer that, over millions of years, behaves like a very slow-moving liquid.
This means that tectonic plates rub against each other over time. They can also slide on top of one other, which is known as subduction. Earthquakes are most common where one plate meets another on the planet. Faults are the exact surfaces where chunks of earth slip past one other. Pressure builds up across the boundaries of plates as they move, while friction holds them in place. When the former overpowers the latter, the earth shakes as the accumulated energy dissipates.
Scientists are well-versed in earthquakes such as those caused by the San Andreas Fault in California and the East Anatolian Fault in Turkey. Earthquakes can, however, occur within tectonic plates as pressure along their edges causes deformations in the center. These threats are more difficult to detect and quantify.
“Our understanding of these within-plate earthquakes is not as good,” said Greg Beroza, a geophysics professor at Stanford University. He said that an earthquake within a tectonic plate has fewer warning symptoms than one along a fault line.
2) The Richter scale isn’t the only measurement game in town anymore
The Richter scale, invented in 1935 by Charles Richter to quantify earthquakes in Southern California, has gone out of favor.
It use a logarithmic scale rather than a linear scale to account for the vast disparity between the smallest tremors and tower-toppling tremors. A magnitude 7 earthquake is 10 times more powerful than a magnitude 6 and 100 times more powerful than a magnitude 5.
The Richter scale measures the peak amplitude of seismic waves, providing an indirect indication of the magnitude of the earthquake. So, if an earthquake is analogous to a rock thrown into a pond, the Richter scale measures the height of the highest wave, not the size of the rock or the extent of the ripples.
In the case of an earthquake, the ripples aren’t flowing through a homogeneous medium like water, but rather through solid rock, which comes in a variety of shapes, sizes, densities, and configurations. Solid rock can also withstand a variety of waves. (While some geologic formations can dampen large earthquakes, others can enhance little tremors.)
While Richter’s scale, which was calibrated to Southern California at the time, was useful for comparing earthquakes, it now presents an incomplete picture of dangers and loses accuracy for stronger events. It also overlooks some of the intricacies of other earthquake-prone places around the world, making it ineffective for individuals trying to build structures to withstand them.
“We can’t use that in our design calculations,” said Steven McCabe, leader of the National Institute of Standards and Technology’s earthquake engineering section. “We’re dealing with displacements.”
One alternate approach to characterize earthquakes is displacement, or how much the ground actually moves. The moment magnitude scale is another. It takes into account numerous types of seismic waves, relying on more precise equipment and better processing to provide a credible yardstick for comparing seismic events.
When you read about the magnitude of an earthquake in the news, such as Turkey’s recent magnitude 7.8 quake, the moment magnitude scale is frequently employed.
However, this is still a proxy for the magnitude of the earthquake. And, according to Marine Denolle, an earthquake researcher at Harvard University, determining the scale of an event, such as the 2004 Indian Ocean earthquake, can take up to a year using just indirect observations.
“We prefer to use peak ground acceleration,” she explains. This is the most useful parameter for engineers since it measures how the speed and direction of the ground change.
So, certainly, earthquake scales have become much more complex and precise throughout time. However, it has also enabled scientists and engineers to collect considerably more precise measurements, which makes a significant difference in preparing for them.
3) We can’t actually anticipate all of them
Predicting earthquakes is a sensitive subject for scientists, in part because it has long been a game played by con artists and pseudoscientists claiming to be able to anticipate earthquakes. (Of course, their statements have crumbled under investigation.)
Scientists have a solid idea of where earthquakes might occur. They can identify probable seismic hot zones and the types of tremors they face by using historical records and geology observations. (You may see an interactive map of fault lines from the US Geological Survey and an interactive map of seismic occurrences from NOAA.)
When earthquakes will occur is still unknown.
“Many seismologists have been working on that problem for many decades.” “We’re not predicting earthquakes in the near future,” Beroza stated. “That requires us to know all kinds of information that we don’t have.”
It’s impossible to predict when an earthquake will occur since the forces that create them happen slowly over a large area yet spread quickly over a small area. What’s astounding is that forces accumulated over millions of years across continents can batter cities in minutes.
Forecasting earthquakes would necessitate high-resolution readings far underground over decades, if not centuries, paired with sophisticated simulations. Even so, it’s unlikely to result in an hour’s worth of lead time. As a result, there are eventually too many variables at work and too few instruments to examine them meaningfully.
Some study indicates that foreshocks can occur before a major earthquake, but they are difficult to differentiate from the hundreds of smaller earthquakes that occur on a regular basis.
Texts and tweets can actually outrun seismic waves on shorter time spans. Warnings from near the epicenter of the 2011 Tohoku earthquake in Japan, for example, reached Tokyo 232 miles away, giving residents around a minute of warning time.
Many countries are already putting in place warning systems that use contemporary electronic communications to detect tremors and send out notifications before the ground shakes, giving them a few precious minutes to seek shelter.
Meanwhile, aftershocks from big earthquakes frequently rattle the affected area. “If we just had one big one, we know there will be smaller ones soon,” Denolle predicted.
When it comes to prediction, scientists obviously want to avoid overpromising and underdelivering, especially when thousands of lives and billions of dollars are at risk. However, even this prudence has had consequences.
Six Italian scientists were sentenced to six years in prison in 2012 for correctly predicting the dangers of a big earthquake in the town of L’Aquila following a small cluster of earthquakes in the region in 2009. A big earthquake happened six days after the experts met to estimate the risk, killing 309 people. Those convictions were ultimately reversed, and the ordeal has served as a case study for how scientists communicate uncertainty and risk to the public.
4) Sorry, but neither your dogs nor you can forecast earthquakes
Animals acting strangely before earthquakes have been reported since ancient Greece. However, an effective pattern is still elusive. When there’s an earthquake and a cute animal to picture, feathered and furry forecasts arise, but this is mostly due to confirmation bias. Animals perform strange things (by our standards) all the time, and we don’t pay attention to them until an earthquake occurs.
“On any given day, there will be hundreds of pets doing things they’ve never done before and have never done afterward,” Beroza said. Bottom line: Don’t wait for unusual animal behavior to warn you of an impending earthquake.
5) Some earthquakes are unmistakably caused by humans
The massive expansion of hydraulic fracturing across the United States has resulted in an earthquake plague. The injection of millions of gallons of wastewater underground causes earthquakes, not the fracturing of shale rock.
According to the scientists, the injected water makes it easier for rocks to move past each other. “When you inject fluid, you lubricate faults,” explained Denolle.
The US Geological Survey refers to these as “induced earthquakes” and reports that the number of earthquakes in Oklahoma increased to 2,500 in 2014, 4,000 in 2015, and 2,500 in 2016.
“The decline in 2016 may be due in part to injection restrictions implemented by state officials,” the USGS said in a statement. “Of the earthquakes that occurred last year, 21 were greater than magnitude 4.0, and three were greater than magnitude 5.0.”
This is an increase from an average of two earthquakes of magnitude 2.7 or larger every year between 1980 and 2000. (“Natural” earthquakes, on the other hand, do not appear to be increasing in frequency, according to Beroza.)
Humans are also creating earthquakes in another way: Rapidly draining water from subterranean reservoirs has also been proved to induce earthquakes in cities such as Jakarta, according to Denolle.
6) Climate change may have a minor impact on earthquakes
Climate change has had little influence on earthquakes, according to scientists. However, they are not ruling out the option.
Massive ice sheets are melting as average temperatures rise, releasing billions of tons of water from exposed land into the ocean and allowing land masses to rebound. This global rebalance could have seismic effects, but no signs of it have yet materialized.
“What might happen is that enough ice melts to unload the crust,” Beroza said, adding that there is no proof for this, nor for which sections of the planet will show a signal. Denolle acknowledged that there could be a mechanism, but she believes that if climate change has any effect on earthquakes, it will be minor.
7) We’ve improved our ability to reduce seismic hazards and save lives
The Ring of Fire, which runs around the Pacific Ocean and includes the Philippines, Japan, Alaska, California, Mexico, and Chile, is home to 90 percent of the world’s earthquakes. The ring also contains three-quarters of the world’s active volcanoes.
Mexico is a particularly intriguing case study. The country is seismically active due to its location on top of three tectonic plates. An earthquake rocked the capital in 1985, killing over 10,000 people. Denolle pointed out that the geography of the location causes earthquakes from adjacent areas to be funneled toward Mexico City, making any seismic activity dangerous.
The Mexican capital is built on the location of the ancient Aztec city of Tenochtitlan, a lake island. The dry lakebed that is now the foundation of the contemporary metropolis magnifies earthquake shaking.
The 1985 earthquake occurred closer to the surface, and the seismic waves it generated were relatively long in duration between peaks and valleys. According to Denolle, this low-frequency vibration causes skyscrapers to sway. “The most recent earthquakes were deeper, so they had a higher frequency,” she explained.
Building codes are the most important factor in preventing earthquake mortality. Buildings that move with the earth while remaining upright can save thousands of lives, but implementing them can be costly and frequently becomes a political issue.
“Ultimately, that information has got to get implemented, and you can pretty much get that implemented in new construction,” McCabe said. “The trickier problem is existing buildings and older stock.”
Earthquake-prone countries are well aware of this: Japan has been rigorous in frequently revising its building rules to withstand earthquakes. Despite Japan’s falling population, the new requirements have contributed to the country’s construction boom.
Mexico has likewise raised construction standards. Following the 1985 earthquake, architects were forced to account for the fragile lakebed soil in the city and tolerate some movement.
Meanwhile, Iran has gone through multiple iterations of its national earthquake resilience construction standards. For years, Alaska has been researching earthquake damage reduction and response measures.
However, codes are not often followed, and the new rules only apply to new construction. A school that fell in a 2017 earthquake in Mexico City was evidently an older structure that was not earthquake-resistant. And, because the more recent earthquakes in Mexico jolted the ground in a different way, several of the buildings that survived the 1985 earthquake collapsed following 2017 tremors.
In countries such as Iran, there is a significant difference between how urban and rural areas are built. More than a quarter of the population lives in rural areas, where dwellings are constructed using traditional materials such as mud bricks and stone rather than reinforced concrete and steel. This contributes significantly to the high number of victims when earthquakes strike distant areas of the country.
The greatest dangers fall on countries that haven’t had a significant earthquake in living memory and, as a result, haven’t prepared for them or lack the resources to do so. Many of the more than 150,000 deaths in Haiti caused by the 2010 magnitude 7.0 earthquake were caused by a lack of a consistent construction code.
8) The big one is definitely coming to America (someday)
The massive one you’ve been hearing about is true.
The New Yorker earned a Pulitzer Prize in 2015 for its reporting on the possibility of a huge earthquake rocking the Pacific Northwest — “the worst natural disaster in the history of North America,” affecting 7 million people across 140,000 square miles.
The prospective quake might have a magnitude of 8.7 to 9.2, which is greater than the greatest predicted earthquake from the San Andreas Fault, which geologists predict will have a magnitude of 8.2.
Large earthquakes are also expected in Japan, New Zealand, and other Ring of Fire countries. We don’t know when these earthquakes will strike; we just have an approximate idea of the typical period between them, which varies by region.
“In the business, we’ve been talking about that [Pacific Northwest] scenario for decades,” said Beroza. “I wouldn’t say we’re overdue, but it could happen at any time.”
“It is a threat,” Denolle said. “We forget about this threat because there hasn’t been an earthquake in a long time.” “Awhile” refers to more than 300 years.
While California has long been bracing itself for large earthquakes through building rules and emergency preparedness, the Pacific Northwest may be caught off guard, though the author of the New Yorker essay, Kathryn Schulz, has helpfully given a preparation guide.