5.8 quake shakes Turkey's Istanbul

An earthquake in the Marmara Sea 70 kilometers west of Istanbul causes citywide distress as schools and some businesses close down for the day. Experts warn Avcılar-Silivri section of North Anatolian Fault may be on move as earthquakes become number one on country agenda after 20 years.

Duvar English

A 5.8 magnitude earthquake shook buildings and damaged a mosque in Istanbul on Thursday, sending some residents rushing from buildings. There were no immediate reports of casualties.

Witnesses in Turkey’s largest city felt buildings sway and said some offices and schools were temporarily evacuated. Distressed people gathered in open areas, trying to reach their children and relatives. Schoolchildren were immediately dismissed and schools closed for the day. Cellular networks were disabled for a few minutes due to overload.

The tremor occurred at a depth of 12.6 km, the Kandilli Observatory and Earthquake Research Institute said, locating its epicentre 70 kilometers (44 miles) west of Istanbul in the Marmara Sea, south of the town of Silivri. It struck at 1:59 p.m. (10:59 GMT).

City Mayor Ekrem Imamoglu said on Twitter there were no immediate reports of damage or severe injuries. Thirty four people were lightly injured, including one person who was reported to have broken their leg after having jumped from a second-floor window. Many citizens set up tents in parks or designated gathering points to spend the night.

In 1999, an earthquake measuring 7.6 struck the city of Izmit, 90 km southeast of Istanbul, killing more than 17,000 people. Since then, experts have been warning the next big earthquake should be expected to occur in the vicinity of Istanbul before 2030. Istanbul denizens have subconsciously been waiting for the earthquake, as shown by the level of panic seen on Thursday. Since 1999, many laws were passed to strengthen or rebuild buildings in preparation for the expected earthquake.

The Richter Magnitude Scale is a logarithmic measurement, which means a 6.0 quake is about 32 times more powerful than a 5.0. Any quake measured above 6.0 is considered a strong earthquake with property damage and casualties expected. Earthquakes above 7.0 are considered catastrophic. The strongest earthquake ever measured with the Richter scale was a 9.4 in 1960, in the Pacific Ocean near Chile. The depth of an earthquake also plays a major role in causing damage, with an earthquake closer to the surface being more dangerous.

The North Anatolian Fault crosses most of Turkey and extends into the Sea of Marmara, a few kilometers below Istanbul, which is home to more than 15 million people.

Istanbul Technical University official statement

Following the second Silivri earthquake on Thursday, experts came forward with various hypotheses regarding a possible big earthquake in Istanbul. Istanbul Technical University academics also released a statement. According to ITU, it is a critical indication that two Silivri earthquakes are located at the end of Kumburgaz segment of the Marmara fault:

"Prof. Dr. A. M. Celal Şengör, who hase been researching the Marmara Fault for many years, ITU Geological Engineering Department Head Prof. Dr. Ziyadin Çakır, Pr. Dr. M. Sinan Özeren and Lecturer Dr. Gülsen Uçarkuş have made assessments to share with the public."

The part of the North Anatolian Fault that extends into Sea of Marmara is usually referred to as the 'Marmara Fault' by geologists. The various parts of the faultline do not all behave the same. For some parts, movements on the floor called 'creep' occur and creates small earthquakes. For other parts of the fault, earthquakes almost never happen. The last big earthquake to happen on the Marmara Fault was the 7.4 magnitude Izmit quake in 1999. The rupture that caused that earthquake moved west towards the sea into the Bay of Izmit.

The Kumburgaz segment of the Marmara fault, which stretches from south of Avcılar to south of Silivri, is understood to be silent, which means it is expected to break. This is known as a seismic gap. Geology, geodesy and seismology studies made on the seafloor of Kumburgaz segment show that it is locked and has not moved for a long time, and thus the next big earthquake is expected to occur there. That two Silivri earthquakes were located at the end of this fault is a critical indicator.

Based on seismology data, we have concluded that both earthquakes and all aftershocks are part of the same mechanical rupture process. Based on scientific indicators, current seismic activity must be followed closely and necessary precautions must be taken. During this time, our university will continue to report expert opinions through the ITU Corporate Communication Office to prevent misinformation."