Source characteristics and seismotectonic implications of 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)

Irmak T. S., Yolsal Çevikbilen S., Eken T., Doğan B., Erman C., Yavuz E., ...More

Geophysical Journal International, vol.227, no.1, pp.383-402, 2021 (SCI-Expanded)

  • Publication Type: Article / Article
  • Volume: 227 Issue: 1
  • Publication Date: 2021
  • Doi Number: 10.1093/gji/ggab233
  • Journal Name: Geophysical Journal International
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, Aerospace Database, Aquatic Science & Fisheries Abstracts (ASFA), Artic & Antarctic Regions, Communication Abstracts, Compendex, Environment Index, Geobase, INSPEC, Metadex, zbMATH, Civil Engineering Abstracts
  • Page Numbers: pp.383-402
  • Kocaeli University Affiliated: Yes

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 the present study, we examine source properties of the mainshock 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 mainshock. The detected aftershock activity appears to focus on the east side of the mainshock 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 mainshock. 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 mainshock 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 Northern Anatolian Fault Zone.