M7.8 and M7.5 Kahramanmaraş Earthquake Sequence near Nurdağı, Turkey (Türkiye)
Earthquake details about the February 6, 2023 quakes.
[Update: February 17, 2023]
Read detailed aftershock statement: M 7.8 - 27 km E of Nurdağı, Turkey (Türkiye)
The recent earthquakes in Turkey (Türkiye) have led to an unbearable loss of life and injuries across the Kahramanmaraş region. During the response and recovery efforts, USGS has continued to provide scientific support to help people in the region make the best decisions for themselves, their families, and their communities.
After large earthquakes, like the M7.8 and M7.5 Kahramanmaraş Earthquake Sequence, it is extremely common for hundreds of aftershocks to occur over the next few weeks, months, or possibly years. Eventually, the frequency of these aftershocks will decrease.
Surface rupture is a phenomenon that occurs during earthquakes when the ground surface breaks and shifts due to the movement of a fault. Last week's earthquake sequence displaced numerous fault segments within the East Anatolian Fault zone, with early estimates indicating around 185 miles of fault length ruptured. Parts of the North Anatolian Fault shifted as much as 10 feet, while segments of the East Anatolian Fault slid over 30 feet. These fault ruptures are visible in satellite and radar imagery.
An aftershock is an earthquake that occurs following, and near the epicenter of, the main large-magnitude earthquake. Because aftershocks are common and follow a typical pattern, scientists can provide information regarding how they might impact areas that have recently experienced a large earthquake. These statements, which sometimes take the form of forecasts, are not predictions, but rather provide a tool that can be used to emphasize likely scenarios describing the number and magnitude of earthquakes that might happen next in the months following the mainshock.
It still remains impossible to predict the exact size, location, and timing of individual earthquakes.
Aftershocks are not always restricted to the same fault system as the mainshock, as large quakes can sometimes trigger aftershocks further away. Most aftershocks will, however, cluster close to the mainshock fault rupture. Typically, the largest aftershock is about a magnitude smaller than the mainshock with most aftershocks being a few orders of magnitude less. Although the M7.5 aftershock was large, it was not out of line with what has happened in past earthquake sequences.
Was the M7.5 earthquake an aftershock or a different main quake?
About one in every 20 large-magnitude earthquakes will have a similar-sized aftershock near it within the first week. That was the case in Turkey, with the M7.8 mainshock being followed by a M7.5 aftershock about 60 miles away just nine hours later. Aftershocks don’t always occur on the same fault as the mainshock, they only need to be close to its epicenter and occur after to be considered an aftershock. It’s worth noting that the M7.5 aftershock did not lower the chance that another large earthquake could still occur. Although the likelihood of future large aftershocks decreases over time, there always remains a small chance one will happen even months later.
What might happen next?
As locals begin the long recovery process, they must still contend with concerns about the likelihood and risk of ongoing aftershocks.
The USGS has put out an aftershock statement for the M7.8 earthquake describing what might happen over the next month. The statement describes three scenarios, with the most likely scenario indicating there is a 90 percent chance that earthquakes will decrease in frequency, with none being larger than M7. In this scenario, moderate aftershocks between M5 and M6 are still likely. These moderate quakes can cause damage, particularly to weakened or older buildings not built to withstand earthquakes. The other two scenarios are less likely, yet more extreme. There is a 10 percent chance an aftershock could be M7.0 and about a one percent chance an aftershock would be of similar size or larger than the M7.8 mainshock.
Regardless of the scenario, smaller magnitude earthquakes between M3 and M4 will continue to be felt by people near the epicenters. Aftershock sequences can last years to decades, long after people stop feeling the increasingly smaller magnitude earthquakes.
For more information:
What's the difference between a foreshock and aftershock?
[Original Posting: February 6, 2023]
On February 6, around 4:15 a.m. local time, a magnitude 7.8 earthquake struck south-central Turkey (Türkiye) near the Turkey/Syria border. Just 11 minutes later, it was followed by a magnitude 6.7 aftershock. The largest aftershock at the time of writing was a M7.5 aftershock which struck 95 km (~60 miles) to the north. USGS observations and analyses indicate all these events are occurring within the East Anatolian fault system.
Though an earthquake of this magnitude is rare anywhere in the world, this type of event is generally expected on long, plate-boundary strike-slip faults.
“It’s difficult to watch this tragedy unfold, especially since we’ve known for a long time that the buildings in the region were not designed to withstand earthquakes,” said USGS scientist David Wald. “An earthquake this size has the potential to be damaging anywhere in the world, but many structures in this region are particularly vulnerable.”
The two largest earthquakes in the recent series are relatively shallow, with the mainshock 18 kilometers, or 11 miles, deep and the 7.5 magnitude aftershock at 10 kilometers (just over 6 miles) deep. Because the quakes are relatively shallow, the intensity of the shaking is severe.
“This earthquake produced intense shaking in the epicentral region,” said USGS scientist Kishor Jaiswal. “While newer buildings in other parts of Turkey (like Istanbul) are designed with modern earthquake standards in mind, the area affected by this earthquake included more vulnerable buildings, like older types of concrete frames that were not designed from seismic considerations to absorb this much ground motion.”
USGS has produced several products indicating likely damage, including a Ground Failure Estimates report that indicates a significant area and population is exposed to both landslide and liquefaction hazards as a result of the shaking.
Another USGS product is a report known as PAGER, short for Prompt Assessment of Global Earthquakes for Response. The PAGER report combines earthquake data, population density and structural vulnerability to estimate the number of people exposed to different amounts of shaking. It also provides estimates of potential fatalities and economic losses. The M7.8 mainshock registered RED for Economic Losses and Orange for Fatalities, indicating extensive damage is probable, the disaster is likely widespread, and that significant casualties are likely. The largest aftershock of magnitude 7.5 itself registered Orange for fatalities and economic losses on the USGS Pager impact report.
USGS is supporting partners in the region, such as the Kandilli Observatory and Earthquake Research Institute, as well other federal agencies by providing information products and images for partners that can help them understand the situation and ongoing risks of aftershocks.
As of February 6 evening (10:30 pm local time), around 30 aftershocks magnitude 4.5 and larger have been recorded between the Mediterranean Sea, 100 km (60 miles) to the southwest, and the city of Malatya, 200 km to the northeast. All of the tremors are taking place within the East Anatolian fault system. Aftershocks are expected to continue in the vicinity, which is a triple junction, a tectonically active area where three tectonic plates -- Anatolia, Arabia, and Africa plates -- touch and interact with each other.
Since 1970, only three earthquakes of magnitude 6 or larger have been registered in this region. The largest was a magnitude 6.7 that occurred January 24, 2020. You can see details about that event here.
For more and updated information on this earthquake, please see the M7.5 event page. The event page for the M7.8 earthquake can be found here.
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