Strong earthquake strikes near the Marmara Fault, damaging 77 buildings and frightening Istanbul residents

Haluk Eyidoğan, Ph.D., Istanbul Technical University, and Volkan Sevilgen, M.S.c., Temblor, Inc.
 
Some 77 public buildings were assessed as heavily damaged. Of the public buildings, 1 hospital, 4 schools, and 9 administrative buildings are severely damaged. Some 29 schools of various degrees of damage were forced to close, at least temporarily.
 
Citation: Eyidogan, H., Sevilgen, V., (2019), Strong earthquake strikes near the Marmara Fault, damaging 77 buildings and frightening Istanbul residents, Temblor, http://doi.org/10.32858/temblor.047
 

In the rush to call relatives after the shaking, cell phone and internet services were temporarily disabled in Istanbul
 

On 26 September 2019, there was a strong earthquake in the Marmara Sea (Northwestern Turkey) with a magnitude of M 5.7 on the Main Marmara Fault (MMF). The public took to the streets without knowing what to do. The press and social media have been shaken by the news with a wide range of information. Some of the mobile phone operators were disabled.

After every strong earthquake in Marmara, questions and discussions continued for hours on maps and graphics, dominated by the question of ‘what is the danger of a still larger earthquake in Marmara’ and the question of whether a larger earthquake would be triggered after this earthquake. In contrast, there was no debate on how to reduce earthquake risks in the megacity of Istanbul.

 

Location of the Main Marmara Fault and major earthquakes during the instrumental earthquake period in the years between 1900 and 2019. Modified from the active fault map of General Directorate of Mineral Research, Turkey.
Location of the Main Marmara Fault and major earthquakes (Altunel et al. 2004; Hubert-Ferrari et al. 2000) during the instrumental earthquake period in the years between 1900 and 2019. Modified from the active fault map of General Directorate of Mineral Research, Turkey; Armijo et al., 2002; Armijo et al., 2005

 
The M 5.7 quake heavily damaged 77 public buildings

The closest settlement to the earthquake episode was Silivri, 22 km to the north, but the earthquake was felt in many places around the Sea of ​​Marmara, including Istanbul. Strong enough to topple some vases and kitchenware, the largest recorded horizontal accelerations were 0.081 g in Silivri and 0.085 g in Büyükçekmece, 34 km away. Istanbul suffered widespread damage to varying degrees. Although the damage assessment is still continuing, according to the latest information, an average of 3,600 buildings have been examined, and 77 public buildings were assessed as heavily damaged. Of the public buildings, 1 hospital, 4 schools, and 9 administrative buildings are severely damaged. Some 29 schools of various degrees of damage were forced to close, at least temporarily.

 

Maximum acceleration in gal versus epicentral distance in km (100% g is 980 cm/s2). The data is from the Disaster and Emergency Management Authority of Turkey (AFAD) data archive (http://kyhdata.deprem.gov.tr/2K/kyhdata_v4.php).
Maximum acceleration in gal versus epicentral distance in km (100% g is 980 cm/s2). The data is from the Disaster and Emergency Management Authority of Turkey (AFAD) data archive (http://kyhdata.deprem.gov.tr/2K/kyhdata_v4.php).

 

The seismic activity of September 26, 2019 earthquake. Modified from the active fault map of General Directorate of Mineral Research, Turkey. The possible ruptured fault with thrust component is shown by red-colored dashed line.
The seismic activity of September 26, 2019 earthquake. Modified from the active fault map of General Directorate of Mineral Research, Turkey. The possible ruptured fault with thrust component is shown by red-colored dashed line. USGS Focal Mechanism

 
North-South cross-section through the aftershocks, showing that the M 4.6 (F/S) and M 5.7 (M/S) struck near but not on the Marmara Fault
North-South cross-section through the aftershocks, showing that the M 4.6 (F/S) and M 5.7 (M/S) struck near but not on the Marmara Fault

 
Seismicity started to ramp up four days before the M 5.7

Four days before the earthquake of magnitude 5.7 on 26 September 2019, four micro-earthquakes of magnitude 2.1-2.2 were recorded in the same area on 22 September 2019. On September 24, 2019, there was an earthquake of 3.0 magnitude in the same place, and 30 minutes after this earthquake, a magnitude 4.6 magnitude was felt near the northern shores of the Marmara Sea. Finally, on September 26, 2019, there was a strong earthquake of 5.7, which was widely felt in the Marmara region, and many people tried to shelter outside their homes for a few nights. Numerous aftershocks followed the magnitude 5.7.

 

The seismic activity in the time period between September 22, 2019 and October 01, 2019. Data is from BU, Kandilli Observatory and Earthquake Research Institute, İstanbul.
The seismic activity in the time period between September 22, 2019 and October 01, 2019. Data is from BU, Kandilli Observatory and Earthquake Research Institute, İstanbul.

 
The M 5.7 was probably not on the main Marmara Fault

The fault rupture orientation as inferred from the recorded seismic waves (‘focal mechanism’) of the 5.7 magnitude earthquake shows that a fault struck on a 45-degree dipping plane with predominant thrust slip. In contrast, the Marmara fault is believed to be near-vertically inclined with ‘right-lateral’ slip (whichever side you are on, the other moves to the right). Therefore, the earthquake most likely occurred on the secondary faults in the Marmara Sea, as also suggested by the alignment of its aftershocks.

Large-double earthquakes caused heavy damage to Istanbul in 1776 (Modified from Parsons et al. 2000), Solid Blue and Red lines show the ruptures, Dashed lines show the maximum possible extent of the ruptures based on damage observations.
Large-double earthquakes caused heavy damage to Istanbul in 1776 (Modified from Parsons et al. 2000), Solid Blue and Red lines show the ruptures, Dashed lines show the maximum possible extent of the ruptures based on damage observations.

 

What’s next?

Earthquake risk for Istanbul still remains high even though the recent seismicity didn’t seem to occur on the Main Marmara Fault, so the continuing effort is needed to prepare the city against future earthquake disasters.

Hagia Sophia in Istanbul has been subject to large earthquake damages since its construction in the year 537, (1482 years ago). It enlightens seismologists about the size of the historical earthquakes thanks to its earthquake damage and repair record.
Hagia Sophia in Istanbul has been subject to large earthquake damages since its construction in the year 537, (1482 years ago). It enlightens seismologists about the size of the historical earthquakes thanks to its earthquake damage and repair record.

 

References

Armijo et al., Asymmetric slip partitioning in the Sea of Marmara pull-apart: a clue to propagation processes of the North Anatolian Fault?, Terra Nova 14,2 DOI: 10.1046/j.1365-3121.2002.00397.x, 2002

Armijo et al., Submarine fault scarps in the Sea of Marmara pull-apart (North Anatolian Fault): Implications for seismic hazard in Istanbul, Geochemistry Geophysics Geosystems, 6, Q06009, DOI: 10.1029/2004GC000896, 2005

Aurélia Hubert-Ferrari, Aykut Barka, Eric Jacques, Süleyman S. Nalbant, Bertrand Meyer, Rolando Armijo, Paul Tapponnier, and Geoffrey C. P. King (2000), Seismic hazard in the Marmara Sea region following the 17 August 1999 Izmit earthquake, Nature, 404, 269–273, doi.org/10.1038/35005054

DDA seismic data from the Government of Turkey,
https://deprem.afad.gov.tr

Erhan Altunel, Mustapha Meghraoui, H. Serdar Akyüz, and Aynur Dikbas (2004), Characteristics of the 1912 co‐seismic rupture along the North Anatolian Fault Zone (Turkey): implications for the expected Marmara earthquake, Terra Nova, 16, 198-204, doi.org/10.1111/j.1365-3121.2004.00552.x

General Directorate of Mineral Research, Turkey

Kandilli Observatory and Earthquake Research Institute

Tom Parsons, Shinji Toda, Ross S. Stein, Aykut Barka, and James H. Dieterich (2000), Heightened odds of large earthquakes near Istanbul: An interaction-based probability calculation, Science, 288, 661-665, doi: 10.1126/science.288.5466.661

U.S. Geological Survey, Focal Mechanism

  • Rolando Armijo

    For sure it is an interesting event. Volkan, your citations to published fault maps are inappropriate. Probably you are unfamiliar with the specific tectonic literature on the North Anatolian Fault and the more specifically in the Marmara region (asking R.S. would have been helpful). But Haluk must be aware of the problem… I don’t understand.

    For your maps you have used, may be unconsciously, a couple of well-known references:
    -The first one presents the original bathymetric data set and the first accurate maps of submarine faults in the Sea of Marmara (Armijo et al., Asymmetric slip partitioning in the Sea of Marmara pull-apart: a clue to propagation processes of the North Anatolian Fault?, Terra Nova 14,2 DOI: 10.1046/j.1365-3121.2002.00397.x, 2002).
    -The second one documents precisely the sea-bottom rupture associated with the 1912 Ms 7.4 earthquake, based on ROV observations (Armijo et al., Submarine fault scarps in the Sea of Marmara pull-apart (North Anatolian Fault): Implications for seismic hazard in Istanbul, Geochemistry Geophysics Geosystems, 6, Q06009, DOI: 10.1029/2004GC000896, 2005).

    I urge you to to compare your first two maps with those in the references above.

    Having said that, let’s see the science. If you inspect the map in figure 4 in Armijo et al. (2002) you will see subsidiary zones of compression (hatched and adorned with black triangles indicating probable thrust dip) identified on the eastern and western sides of the central pull-apart. Note that those zones strike approximately NE-SW so parallel to the extension direction in the rhomb-shaped pull-apart (indicated by yellow arrows). The compressional zone to the East of the central pull-apart apparently forms a >5km long pressure ridge presumably over a steep SE-dipping thrust fault. Interestingly, the reportedly compressional event of September 26, 2019 (Mw 5.7) had an epicentre located no far from to the eastern compressional zone, with one nodal plane striking NE and dipping SE.

    Yours,
    Sincerely,

    Rolando Armijo

  • Temblor

    Dear Rolando,

    You are right that we should have added your papers in the references. My apologies. I now added them to the articles.

    I also like your interpretation of the possible fault for this event. Would you like to write an article at Temblor about this? We assign DOI and ISSN numbers so that the Temblor articles are citable publications as well as listed in Google Scholar. We aim to make Temblor a rapid publication platform so vital science becomes useful as soon as possible.

    Best,
    Volkan

    Volkan Sevilgen, M.Sc
    CTO & Co-founder, Temblor, Inc.
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  • Ziyadin Cakir

    Dear Volkan and Rolando,

    I would like to inform you both that detail analysis of the event by Karabulut and his colleagues indicates that the thrust component is negligible (<20 degrees) and the dip direction of the fault is NE. The rupture coincides well with the fault splay given in Armijo et al., 2005 (fig. 2).

    Regards,
    Ziya