ABSTRACT
The Central Marmara Sea
region hosts the northwestern branch of the North Anatolian Fault Zone (NAFZ)
with its known seismic gap between the 1912 Ganos (Mw 7.2)
and 1999 Izmit (Mw 7.4) major devastating earthquakes
and thus poses a significant seismic hazard potential for the megacity
Istanbul. The 26 September 2019 Mw 5.7 Silivri
High-Kumburgaz Basin (central Marmara Sea) earthquake ruptured a thrust fault
with a minor strike-slip component at the north of the eastern end of this gap
relatively in the shallow depth (h= 8 km) range. Thus, in this
study, we examine source properties of the main shock activity and coseismic
behaviour of the failure, and the pattern of post-seismic deformation based on
the aftershock distribution to have an insight into the role of the subsidiary
and main fault structures on the crustal kinematics along this complicated
branch of the NAFZ. The relocated epicentres are aligned in the E–W direction
and tend to propagate towards the segments to the east of the main shock. The
detected aftershock activity appears to focus on the east side of the main
shock and almost no seismic activity was observed to the west of the epicentre.
Independent investigations from coda-wave fitting, point-source, and
finite-fault slip modelling agree on the moment magnitude of Mw5.7
for the 26 September 2019 main shock. The kinematic rupture model of this event
implied that the main rupture nucleated around the hypocentre, and then propagated
bilaterally along the E–W direction but with significant progress towards the
east. The distribution of the slip vectors indicates that the rupture evolved
on a dextral thrust fault plane. The spatio-temporal behaviour of the overall
aftershocks sequence, their focal mechanism solutions and our kinematic slip
model clearly shows that the existing secondary structures developed in simple
shear dextral deformation are likely responsible for the main shock activity.
We conclude that such type of deformation model results in a motion in response
to the thrust faulting with strike-slip component with an N89°W (271°)
orientation and 33°NE dipping at left stepover transpressional region on the
NAFZ.
Authors: T. Serkan Irmak, Seda Yolsal Çevikbilen, Tuna Eken, Bülent Doğan, Ceyhun Erman, Evrim Yavuz, Hakan Alçık, Peter Gaebler, Ali Pınar, Tuncay Taymaz
Journal: Geophysical Journal International
Year: 2021
DOI: 10.1093/gji/ggab233
Cite this article: Irmak, T. S., Yolsal-Çevikbilen, S., Eken, T., Doğan, B., Erman, C., Yavuz, E., Alçık, H., Gaebler, P., Pınar, A., Taymaz, T. (2021). Source characteristics and seismotectonic implications of the 26 September 2019 Mw 5.7 Silivri High-Kumburgaz Basin earthquake and evaluation of its aftershocks at the North Anatolian Fault Zone (Central Marmara Sea, NW Turkey). Geophysical Journal International, 227(1), 383-402.
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