Fault spatial heterogeneity and seismic hazards revealed by geodetic observations of the East Anatolian Fault

The quasi-cyclic behavior of fault zones, which encompasses interseismic, coseismic, and postseismic phases, is essential for understanding the dynamic evolution of earthquakes. Examining the spatiotemporal evolution of surface deformation and fault slip distribution across different periods of an earthquake cycle, obtained through geodetic techniques, enables a systematic and precise understanding of earthquake deformation models. The 2020 Elaziğ earthquake and the 2023 Kahramanmaraş Earthquake Sequence, both of which occurred along the East Anatolian Fault (EAF) in eastern Anatolia, provide a unique opportunity for studying the earthquake cycle and associated fault behavior. Historically, seismic activity along the EAF has demonstrated the fault’s capacity to produce significant earthquakes, with distinctive fault mechanisms varying across time and fault segments. In addition, approximately a decade of high-resolution surface deformation data obtained from InSAR, spanning five distinct periods in the earthquake cycle, is available for in-depth analysis.

Our objective was to provide a comprehensive characterization of present-day kinematic processes along the EAF, to gain insights into fault frictional properties and to assess potential future seismic hazards. To do so, we utilized high-resolution interferometric data to investigate fault slip evolution from March 2015 to June 2024. This temporally continuous deformation field allowed us to explore fault behavior and develop complete slip distribution models throughout the earthquake cycle, which includes an interseismic period (2015-2020), two postseismic periods (2020-2023 and 2023-2024), and three coseismic events. Initially, we conducted an InSAR time series analysis to capture the deformation fields across different periods of the EAF earthquake cycle. We then integrated high-resolution ground displacement data, aftershock distributions from the 2020 and 2023 earthquakes, and the Global Active Faults Database (GEM) to map the complex fault geometries of the EAF. These inputs facilitated the creation of triangular dislocation models for analyzing fault slip distribution at various periods of the earthquake cycle. Moreover, we examined the relationship between slip distribution and estimated frictional parameters along the EAF, followed by an assessment of seismic hazard potential.

Our analysis of slip evolution reveals that the postseismic fault slip following the 2020 and 2023 earthquakes primarily occurred in areas with minimal coseismic slip. We also identified four slip deficit regions, comprising both shallow and deep portions of the seismogenic faults. By integrating slip distributions and historical earthquakes, we calculated the total moment deficit rate for each fault segment, revealing that the Palu segment, as well as the central portions of the Erkenek and Sürgü-Çardak segment, possesses a high earthquake potential. These findings underscore the critical need for high-resolution and continuous monitoring of fault systems across different seismic periods, offering new insights into the dynamics of the earthquake cycle along the EAF.