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.

1. Strong earthquake strikes near the Marmara Fault, damaging 77
buildings and frightening Istanbul residents
POSTED ON OCTOBER 5, 2019 BY TEMBLOR
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: Eyidoğan, 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 (Altunel et al. 2004; Hubert-
Ferrari et al. 2000) during the instrumental earthquake period in the years between 1900 and

2. 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).

3. 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

4. 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

5. 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 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.

6. 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.

7. 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