Jaime Toro, Professor of Geology, West Virginia University
Sun, October 15, 2023
THE CONVERSATION
A man works his way through the rubble of buildings in Marrakesh, Morocco, after a magnitude 6.8 earthquake on Sept. 8, 2023. Fadel Senna/AFP via Getty Images
Earthquakes, large and small, happen every single day along zones that wrap around the world like seams on a baseball. Most don’t bother anybody, so they don’t make the news. But every now and then a catastrophic earthquake hits people somewhere in the world with horrific destruction and immense suffering.
On Oct. 7, 2023, a 6.3 magnitude earthquake struck near the historic city of Herat, Afghanistan, leaving more than 1,000 people dead in the rubble, according to estimates. It was followed by two more earthquakes, just as powerful, on Oct. 11 and Oct. 15. A few weeks earlier, on Sept. 8, a 6.8 magnitude earthquake shook ancient villages apart in the Atlas Mountains of Morocco, killing nearly 3,000 people. In February 2023, a large area of Turkey and Syria was devastated by two major earthquakes that hit in close succession.
As a geologist, I study the forces that cause earthquakes. Here’s why some seismic zones are very active while others may be quiet for generations before the stress builds into a catastrophic event.
Earth’s crust crashes into itself and pulls apart
Earthquakes are part of the normal behavior of the Earth. They occur with the movement of the tectonic plates that form the outer layer of the planet.
You can think of the plates as a more or less rigid outer shell that has to shift to allow the Earth to give off its internal heat.
A map of all earthquakes greater than magnitude 5 from 1960 to 2023 clearly shows the outlines of the tectonic plates. USGS/GMRT
These plates carry the continents and the oceans, and they are continuously in slow-motion crashes with one another. The cold and dense oceanic plates dive under continental plates and back into Earth’s mantle in a process known as subduction. As an oceanic plate sinks, it drags everything behind it and opens a rift somewhere else that is filled by rising hot material from the mantle that then cools. These rifts are long chains of underwater volcanoes, known as mid-ocean ridges.
Earthquakes accompany both subduction and rifting. In fact, that is how the plate boundaries were first discovered.
In the 1950s, when a global seismic network was established to monitor nuclear tests, geophysicists noticed that most earthquakes occur along relatively narrow bands that either fringe the edges of ocean basins, as in the Pacific, or cut right down the middle of basins, as in the Atlantic.
They also noticed that earthquakes along subduction zones are shallow on the oceanic side but get deeper under the continent. If you plot the earthquakes in 3D, they define slablike features that trace the plates sinking into the mantle.
Ten thousand earthquake locations from 1980 to 2009 trace the Pacific Plate as it subducts under northern Japan. The top image is a side view showing the depth of the earthquakes beneath the rectangle on the map. Jaime Toro, CC BY-ND
An experiment: How an earthquake works
To understand what happens during an earthquake, put the palms of your hands together and press with some force. You are modeling a plate boundary fault. Each hand is one plate, and the surface of your hands is the fault. Your muscles are the plate tectonic system.
Now, add some forward force to your right hand. You will find that it will eventually jerk forward when the forward force overcomes the friction between your palms. That sudden forward jerk is the earthquake.
A Google Earth image of creeks offset by movement along the San Andreas Fault in Southern California as the Pacific Plate moves to the northwest with respect to North America. Jaime Toro
Scientists explain earthquakes using what’s known as the elastic rebound theory.
Fast plates move at up to 8 inches (20 centimeters) per year, driven mostly by the oceanic slabs sinking at subduction zones. Over time, they become stuck to each other by friction at the plate boundary. The attempted motion deforms the plate boundary zone elastically, like a loaded spring. At some point, the accumulated elastic energy overcomes the friction and the plate jerks forward, causing an earthquake.
But the plate-driving forces do not stop, so the plate boundary starts to accumulate elastic energy again, which will cause another earthquake – perhaps soon or perhaps far in the future.
In the oceans, plate boundaries are narrow and well defined because the underlying rocks are very stiff. But within the continents, plate boundaries are often broad zones of deformed mountainous terrain crisscrossed by many faults. Those faults may persist for eons, even if the plate boundary becomes inactive. That is why sometimes earthquakes occur far from plate boundaries.
Earthquakes, fast and slow
The cyclic behavior of faults allows seismologists to estimate earthquake risks statistically. Plate boundaries with fast motions, such as the ones along the Pacific rim, accumulate elastic energy rapidly and have the potential for frequent large-magnitude earthquakes.
Slow-moving plate boundary faults take longer to reach a critical state. Along some faults, hundreds or even thousands of years can pass between large earthquakes. This allows time for towns to grow and for people to lose ancestral memory of past earthquakes.
The earthquake near Herat, Afghanistan, on Oct. 7, 2023, shook rural homes apart. Muhammad Balabuluki/Middle East Images/Middle East Images via AFP
The earthquake in Morocco is an example. Morocco is located on the boundary between the African and the Eurasian plates, which are slowly crashing into each other.
The huge belt of mountains that extends from the Atlas of North Africa to the Pyrenees, Alps and most of the mountains across southern Europe and the Middle East is the product of this plate collision. Yet because these plate motions are slow near Morocco, large earthquakes are not so frequent.
Afghanistan is more prone to earthquakes. It has numerous faults created by the collision of India against Eurasia. The Indian Plate, which is old and stiff, has been plowing into the southern margin of Eurasia for the past 40 million years. You can see evidence of this slow-moving collision in the way the mountain chains – and the earthquakes – wrap around either side of India.
Preparing for the big one
An important fact about catastrophic earthquakes is that, in most cases, the earthquakes don’t kill people – falling buildings do.
Most Americans have heard of California’s San Andreas Fault and the seismic risk to San Francisco and Los Angeles. The last major earthquake along the San Andreas Fault hit at Loma Prieta, in the San Francisco Bay area, in 1989. Its magnitude, 6.9, was comparable to that of the earthquake in Morocco, yet 63 people died compared with thousands. That’s largely because building codes in these earthquake-prone U.S. cities are now designed to keep structures standing when the Earth shakes.
The exceptions are tsunamis, the huge waves generated when an earthquake shifts the seafloor, displacing the water above it. A tsunami that hit Japan in 2011 had horrific consequences, regardless of the quality of engineering in coastal towns.
Unfortunately, earthquake scientists can’t predict exactly when an earthquake might occur; they can only estimate the hazard.
This article, originally published Sept. 13, 2023, has been updated with another powerful earthquake in Afghanistan.
This article is republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts. The Conversation has a variety of fascinating free newsletters.
It was written by: Jaime Toro, West Virginia University.
Read more:
Marrakech artisans – who have helped rebuild the Moroccan city before – are among those hit hard in the earthquake’s devastation
Seismologists can’t predict an impending earthquake, but longer-term forecasts and brief warnings after one starts are possible
Earthquakes can change the course of rivers – with devastating results. We may now be able to predict these threats
Jaime Toro has received funding from NSF, USGS and DOE in the past.
World Food Program says it needs $19M for Afghan earthquake victims
Clyde Hughes
Wed, October 18, 2023 at 8:26 AM MDT·2 min read
0
People affected by an earthquake salvage their belongings as they wait for relief in the Zinda Jan district of Herat, Afghanistan, on October 8. The World Food Program is calling for $19 million in donations to help survivors. Photo by Samiullah Popal/EPA-EFE
Oct. 18 (UPI) -- The World Food Program on Wednesday appealed for $19 million to help Afghans who lost their homes and ability to feed themselves after a series of devastating earthquakes in the western region of the country this month.
The United Nations agency said that emergency food assistance is needed for 100,000 people in light of the earthquakes.
Twin earthquakes rocked the Herat province on Sunday, hospitalizing more than 100 people. Afghanistan was again rocked by earthquakes on Sunday, killing at least one person and injuring more than 100 others.
United Nations pledged $5 million in emergency reserves in response to Afghanistan's recovery from Saturday's devastating 6.3-magnitude earthquake. On Oct. 7, the first devastating earthquake left thousands without homes and 1,400 killed.
An estimated 25,000 buildings have been destroyed, leaving many to sleep in tents next to the rubble of their homes as they fear more earthquakes and aftershocks.
"WFP is assisting the survivors, but we are having to take this food from an already severely underfunded program in Afghanistan and we urgently need additional funding," said Ana Maria Salhuana, deputy country director of WFP Afghanistan.
"Disasters like these earthquakes pound communities who are already barely able to feed themselves back into utter destitution."
The WFP said with the winter months coming, the organization is planning on assisting families with cash transfers and food for three to seven months. The organization was forced to reduce the amount of its assistance because of a funding shortage. The WFP said it can only help one in five people who qualify for assistance.
A man works his way through the rubble of buildings in Marrakesh, Morocco, after a magnitude 6.8 earthquake on Sept. 8, 2023. Fadel Senna/AFP via Getty Images
Earthquakes, large and small, happen every single day along zones that wrap around the world like seams on a baseball. Most don’t bother anybody, so they don’t make the news. But every now and then a catastrophic earthquake hits people somewhere in the world with horrific destruction and immense suffering.
On Oct. 7, 2023, a 6.3 magnitude earthquake struck near the historic city of Herat, Afghanistan, leaving more than 1,000 people dead in the rubble, according to estimates. It was followed by two more earthquakes, just as powerful, on Oct. 11 and Oct. 15. A few weeks earlier, on Sept. 8, a 6.8 magnitude earthquake shook ancient villages apart in the Atlas Mountains of Morocco, killing nearly 3,000 people. In February 2023, a large area of Turkey and Syria was devastated by two major earthquakes that hit in close succession.
As a geologist, I study the forces that cause earthquakes. Here’s why some seismic zones are very active while others may be quiet for generations before the stress builds into a catastrophic event.
Earth’s crust crashes into itself and pulls apart
Earthquakes are part of the normal behavior of the Earth. They occur with the movement of the tectonic plates that form the outer layer of the planet.
You can think of the plates as a more or less rigid outer shell that has to shift to allow the Earth to give off its internal heat.
A map of all earthquakes greater than magnitude 5 from 1960 to 2023 clearly shows the outlines of the tectonic plates. USGS/GMRT
These plates carry the continents and the oceans, and they are continuously in slow-motion crashes with one another. The cold and dense oceanic plates dive under continental plates and back into Earth’s mantle in a process known as subduction. As an oceanic plate sinks, it drags everything behind it and opens a rift somewhere else that is filled by rising hot material from the mantle that then cools. These rifts are long chains of underwater volcanoes, known as mid-ocean ridges.
Earthquakes accompany both subduction and rifting. In fact, that is how the plate boundaries were first discovered.
In the 1950s, when a global seismic network was established to monitor nuclear tests, geophysicists noticed that most earthquakes occur along relatively narrow bands that either fringe the edges of ocean basins, as in the Pacific, or cut right down the middle of basins, as in the Atlantic.
They also noticed that earthquakes along subduction zones are shallow on the oceanic side but get deeper under the continent. If you plot the earthquakes in 3D, they define slablike features that trace the plates sinking into the mantle.
Ten thousand earthquake locations from 1980 to 2009 trace the Pacific Plate as it subducts under northern Japan. The top image is a side view showing the depth of the earthquakes beneath the rectangle on the map. Jaime Toro, CC BY-ND
An experiment: How an earthquake works
To understand what happens during an earthquake, put the palms of your hands together and press with some force. You are modeling a plate boundary fault. Each hand is one plate, and the surface of your hands is the fault. Your muscles are the plate tectonic system.
Now, add some forward force to your right hand. You will find that it will eventually jerk forward when the forward force overcomes the friction between your palms. That sudden forward jerk is the earthquake.
A Google Earth image of creeks offset by movement along the San Andreas Fault in Southern California as the Pacific Plate moves to the northwest with respect to North America. Jaime Toro
Scientists explain earthquakes using what’s known as the elastic rebound theory.
Fast plates move at up to 8 inches (20 centimeters) per year, driven mostly by the oceanic slabs sinking at subduction zones. Over time, they become stuck to each other by friction at the plate boundary. The attempted motion deforms the plate boundary zone elastically, like a loaded spring. At some point, the accumulated elastic energy overcomes the friction and the plate jerks forward, causing an earthquake.
But the plate-driving forces do not stop, so the plate boundary starts to accumulate elastic energy again, which will cause another earthquake – perhaps soon or perhaps far in the future.
In the oceans, plate boundaries are narrow and well defined because the underlying rocks are very stiff. But within the continents, plate boundaries are often broad zones of deformed mountainous terrain crisscrossed by many faults. Those faults may persist for eons, even if the plate boundary becomes inactive. That is why sometimes earthquakes occur far from plate boundaries.
Earthquakes, fast and slow
The cyclic behavior of faults allows seismologists to estimate earthquake risks statistically. Plate boundaries with fast motions, such as the ones along the Pacific rim, accumulate elastic energy rapidly and have the potential for frequent large-magnitude earthquakes.
Slow-moving plate boundary faults take longer to reach a critical state. Along some faults, hundreds or even thousands of years can pass between large earthquakes. This allows time for towns to grow and for people to lose ancestral memory of past earthquakes.
The earthquake near Herat, Afghanistan, on Oct. 7, 2023, shook rural homes apart. Muhammad Balabuluki/Middle East Images/Middle East Images via AFP
The earthquake in Morocco is an example. Morocco is located on the boundary between the African and the Eurasian plates, which are slowly crashing into each other.
The huge belt of mountains that extends from the Atlas of North Africa to the Pyrenees, Alps and most of the mountains across southern Europe and the Middle East is the product of this plate collision. Yet because these plate motions are slow near Morocco, large earthquakes are not so frequent.
Afghanistan is more prone to earthquakes. It has numerous faults created by the collision of India against Eurasia. The Indian Plate, which is old and stiff, has been plowing into the southern margin of Eurasia for the past 40 million years. You can see evidence of this slow-moving collision in the way the mountain chains – and the earthquakes – wrap around either side of India.
Preparing for the big one
An important fact about catastrophic earthquakes is that, in most cases, the earthquakes don’t kill people – falling buildings do.
Most Americans have heard of California’s San Andreas Fault and the seismic risk to San Francisco and Los Angeles. The last major earthquake along the San Andreas Fault hit at Loma Prieta, in the San Francisco Bay area, in 1989. Its magnitude, 6.9, was comparable to that of the earthquake in Morocco, yet 63 people died compared with thousands. That’s largely because building codes in these earthquake-prone U.S. cities are now designed to keep structures standing when the Earth shakes.
The exceptions are tsunamis, the huge waves generated when an earthquake shifts the seafloor, displacing the water above it. A tsunami that hit Japan in 2011 had horrific consequences, regardless of the quality of engineering in coastal towns.
Unfortunately, earthquake scientists can’t predict exactly when an earthquake might occur; they can only estimate the hazard.
This article, originally published Sept. 13, 2023, has been updated with another powerful earthquake in Afghanistan.
This article is republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts. The Conversation has a variety of fascinating free newsletters.
It was written by: Jaime Toro, West Virginia University.
Read more:
Marrakech artisans – who have helped rebuild the Moroccan city before – are among those hit hard in the earthquake’s devastation
Seismologists can’t predict an impending earthquake, but longer-term forecasts and brief warnings after one starts are possible
Earthquakes can change the course of rivers – with devastating results. We may now be able to predict these threats
Jaime Toro has received funding from NSF, USGS and DOE in the past.
World Food Program says it needs $19M for Afghan earthquake victims
Clyde Hughes
Wed, October 18, 2023 at 8:26 AM MDT·2 min read
0
People affected by an earthquake salvage their belongings as they wait for relief in the Zinda Jan district of Herat, Afghanistan, on October 8. The World Food Program is calling for $19 million in donations to help survivors. Photo by Samiullah Popal/EPA-EFE
Oct. 18 (UPI) -- The World Food Program on Wednesday appealed for $19 million to help Afghans who lost their homes and ability to feed themselves after a series of devastating earthquakes in the western region of the country this month.
The United Nations agency said that emergency food assistance is needed for 100,000 people in light of the earthquakes.
Twin earthquakes rocked the Herat province on Sunday, hospitalizing more than 100 people. Afghanistan was again rocked by earthquakes on Sunday, killing at least one person and injuring more than 100 others.
United Nations pledged $5 million in emergency reserves in response to Afghanistan's recovery from Saturday's devastating 6.3-magnitude earthquake. On Oct. 7, the first devastating earthquake left thousands without homes and 1,400 killed.
An estimated 25,000 buildings have been destroyed, leaving many to sleep in tents next to the rubble of their homes as they fear more earthquakes and aftershocks.
"WFP is assisting the survivors, but we are having to take this food from an already severely underfunded program in Afghanistan and we urgently need additional funding," said Ana Maria Salhuana, deputy country director of WFP Afghanistan.
"Disasters like these earthquakes pound communities who are already barely able to feed themselves back into utter destitution."
The WFP said with the winter months coming, the organization is planning on assisting families with cash transfers and food for three to seven months. The organization was forced to reduce the amount of its assistance because of a funding shortage. The WFP said it can only help one in five people who qualify for assistance.
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