Complex multi-fault rupture and triggering during the 2023 earthquake doublet in southeastern Türkiye.

Area of Science:

• Geophysics
• Seismology
• Tectonics

Background:

• The February 6, 2023, earthquakes (M_W 7.8 and M_W 7.7) on the East Anatolian Fault Zone (EAFZ) caused catastrophic damage and fatalities.
• The EAFZ is a major left-lateral strike-slip fault system in a seismically active region.

Purpose of the Study:

• To derive kinematic rupture models for the two major earthquakes.
• To understand the rupture dynamics, including speed, slip distribution, and fault interaction.
• To assess the role of stress transfer in triggering the earthquake doublet.

Main Methods:

• Inversion of extensive seismic and geodetic observations.
• Development of complex 5-6 segment fault models.
• Constraining models with satellite observations and relocated aftershocks.

Main Results:

• The M_W 7.8 event initiated on a splay fault and propagated ~350 km along the main EAFZ strand with slip up to 8.1 m and speeds of 2.5-4.5 km/s.
• The M_W 7.7 event ruptured ~160 km along the northern EAFZ strand, exhibiting initial supershear rupture velocities (>4 km/s) followed by slower speeds (~3 km/s).
• Coulomb stress analysis suggests the first event likely triggered the second and loaded adjacent faults.

Conclusions:

• Detailed kinematic models provide insights into the complex rupture processes of the EAFZ earthquakes.
• The findings highlight the significant role of static stress changes in the triggering of sequential large earthquakes.
• Understanding these rupture dynamics is crucial for seismic hazard assessment in the region.