Seismological Aspects of Doublet Earthquakes Mw 7.8, and Mw 7.6, 6th February 2023, Türkiye/Syria Earthquake and Its Aftershocks: Causes and Consequences

Two devastating earthquakes occurred on the Eastern Anatolian Fault Zone (EAFZ), measuring 7.8 and 7.6 moment magnitudes (Mw), struck Türkiye and Syria on February 6, 2023. The first earthquake Mw7.8 took place on the EAFZ in Pazarcik district of Kahramanmaras city and the second earthquake (Mw7.6) was on Cardak Fault (CF, an E-W aligned segment of the EAFZ) in Elbistan district of the same city. The first earthquake on EAFZ and the second earthquake on CF reveal dominant sinistral strike-slip character according to focal mechanisms solutions of aftershocks (e.g., Mw = 6.8, Mw = 6.4). Total number of aftershocks exceeds 58,000 as of November 2023. Destructive earthquakes have resulted significant impact on 11 cities in Türkiye and 5 provinces in Syria. Doublet earthquakes (compound earthquake) and aftershocks have caused remarkable surface rupture that exhibit horizontal and vertical slips along NE-SW oriented EAFZ (400 × 40 km2) and E-W aligned CF (250 × 40 km2). Based on the seismicity analysis, 88% (45 events over 51 of the aftershocks with magnitudes greater or equal to 5.0 occurred within the first three days following the Mw = 7.8 mainshock. The state of stress from 1977 to the Kahramanmaras doublet earthquakes (DEQ), was almost shear stress regime whereas it reveals between extension (normal) to strike-slip regime. The CF zone area exhibits a dominant shear stress regime. The Kahramanmaras earthquake has generated remarkable set of surface ruptures about ~ 500 km, in total (~ 350 km long for EAFZ and ~ 150 km for CF) with a dominant sinistral strike-slip character. These ruptures could be observed mainly from the south of Hatay city up to north of Celikhan district along the EAFZ, and between Goksun district and Kelhalil village along the CF. Seismic gaps with low geodetic strain rates and low background seismicity were observed between Islahiye (Hatay city) and Nurdagi (Gaziantep city) districts, and around Pazarcik district (Kahramanmaras city). The largest peak ground acceleration (PGA) was recorded by Pazarcik station (Code: 4614) with about 2 g (2039 gal) in the EW component. The next target location for destructive earthquake could be on the Cyprus arc towards Island with the potential to cause a tsunami, or could occur along the DSF by affecting Syria and Lebanon. The EAFZ is an important reminder that large faults can generate very large earthquakes on multiple segments as Türkiye and Syria have experienced during and after the Mw = 7.8 mainshock.