After two incredibly deadly earthquakes in Turkey and a large portion of the Middle East, at least 7,000 people have died and countless others are still missing. Aleppo in northern Syria, a country mired in a horrific civil war and now experiencing compounding tragedies, was particularly heavily struck.

Several have questioned the cause of the earthquakes, how long aftershocks may be anticipated, and how catastrophic the series was amid the protracted rescue, recovery, and rebuilding process that lies ahead.

We have outlined seven essential earthquake sequences knowledge points.

What caused the earthquakes in Turkey? Major issues addressed

When you drop a stone in a body of water to cause a disturbance, the waves continue to propagate for a while afterward, just like ocean waves. The same applies to earthquakes.

According to the U.S. Geological Survey, the actual slip that caused the 7.8-magnitude earthquake took place over a period of about 75 seconds. That earthquake probably caused one to two minutes of trembling for the majority of people in Turkey.

There were tremors felt all across the planet.

Seismometers from all over the world registered the trembling caused by the earthquakes in Turkey.

Yet that is entirely typical. The equivalent of a dime placed under one corner of North America can be detected by seismometers in the Global Seismic Network.

By creating a record section, scientists can see how the seismic waves develop. They may see the path of the earthquake waves by stacking plots from seismometers all over the world, as shown below (with distance on the vertical axis and time going from left to right).

Thus, certainly, waves from the Turkish earthquakes were detected by ultrasensitive seismometers even in Canada, Alaska, Mexico, and Australia.

The second earthquake was it an aftershock? What made it so large?

Aftershocks frequently continue to happen for several weeks or months following the primary earthquake in a sequence. With time, they often become less intense and less frequent.

According to USGS, there is a 1 in 15 possibility that a certain earthquake is a “foreshock” that comes before a larger quake. Although it’s unlikely in this instance, it can happen. (Example: the July 4-6, 2019, Ridgecrest, California, earthquake sequence, which featured a 6.4-magnitude main shock and a 7.1-magnitude secondary shock.))

The first 7.8-magnitude earthquake in Turkey occurred near Nurdagi at 4:15 a.m. local time on Monday. Nine hours later, a shallow 7.5-magnitude quake occurred 60 miles to the north. Although it was an unusually intense aftershock, this situation makes it harder to classify it as an aftershock. Why?

We may identify two distinct clusters of activity if we examine a map of the region’s seismicity and annotate both our 7.8-magnitude and following 7.5 quakes:

Because of this, the 7.5-magnitude earthquake was not an aftershock on the same fault but rather a secondary main shock caused by the initial 7.8-magnitude earthquake to the south.

Seismologist and researcher Judith Hubbard told The Washington Post that there was “room for debate” and that, given its size, she would classify the second earthquake as a second mainshock. Although aftershocks are not required to occur on the original fault, because of the second earthquake’s strength, it stands out and is not a normal aftershock.

Turkey is located at the confluence of three tectonic plates, which makes it a location of severe seismic unrest and makes it particularly sensitive to earthquakes. Nonetheless, the severity of each quakes makes them distinct.

Only three earthquakes with a magnitude of 6 or higher have been recorded in this area since 1970, according to the USGS. “The greatest occurred on January 24, 2020, with a magnitude of 6.7.

What caused the initial earthquake?

The USGS releases details on the process that caused an earthquake soon after it occurs. It came to the conclusion that a strike slip or two faults sliding laterally against each other caused the 7.8 quake. When both masses of the Earth’s crust shifted to the left of one another in this instance, it was a “left lateral” strike slip.

Very likely, it happened on the East Anatolian Fault.

All of the associated earthquake activity, according to the USGS, was “occurring within the East Anatolian fault system,” which is depicted on the map below:

The Anatolian and Arabian plates rub and slide against one another along the East Anatolian Fault. This causes constant stress, which occasionally manifests as catastrophic slips. (Far to the northeast, the Bitlis-Zagros Fold and Thrust Belt is where the Arabian Plate collides with the Eurasian Plate, creating the Zagreb, Alborz, and Caucasus mountains.)

The Arabian Plate is sliding north-northwest along the East Anatolian Fault at a rate of roughly 15 millimeters (0.59 inches) per year, while the Anatolian Plate is sliding west-southwest at a rate of 22 millimeters (0.87 inches) per year:

With relation to one another, the two plates are sliding at a rate of 15 millimeters per year.

The two land masses slipped passed one another by around 10 feet.

The two land masses “slid” past one another by up to 10 to 12 feet (approximately 3 to 3.5 meters) during the 7.8-magnitude earthquake’s “slip,” according to the USGS.

About 50 kilometers, or 30 miles, from the epicenter, the biggest slip happened.

To what extent did the fault rupture? According to the USGS, a section of just over 250 kilometers—or nearly 150 miles—slipped.

Nevertheless, according to alternative USGS models, the earthquake may have only partially ruptured the fault but had a stronger rupture along the “dip,” or the vertical boundary between the two masses of crust.

According to USGS modeling, the slip’s area measured around 60 miles long and 45 miles broad.

Up to 40 centimeters per second, or 15 to 16 inches per second, the ground was also moving. That might not seem like much, but imagine if you were to nudge a house, an office building, or any other structure by that much while doing a series of erratic rolls and jerks back and forth.

At its maximum, the ground experienced an acceleration of 40 percent of one “g,” or the force of gravity. When you leap into the air, gravity accelerates and pulls you back to the ground. Imagine the entire landscape being affected by a force equal to 40% of that acceleration. That demonstrates the earthquake’s strength.

Stress that had been bottled up for centuries was let out.

Simple math can be used to estimate how long this earthquake has been in the making.

Let’s assume that the East Anatolian Fault—which cannot be proven with certainty but is the most likely location—was where the earthquake took place. One can multiply the annual displacement of the plates relative to one another by the entire amount of the slide (10 feet) (15 millimeters, or 0.6 inches). That would imply a 200-year accumulation of stress.

That estimate might be conservative. Hubbard claimed on Twitter that the tension may have accumulated over a 300-year period.