Fault interactions in a complex fault system: insight from the 1936–1997 NE Lut earthquake sequence

Abstract

Summary Calculations of Coulomb stress changes have shown that moderate to large earthquakes may increase stress at the location of future earthquakes. Coulomb stress transfers have thus been widely accepted to explain earthquake sequences, especially for sequences occurring within parallel or collinear fault systems. Relating, under this framework, successive earthquakes occurring within more complex fault systems (i.e. conjugate fault system) is more challenging. In this study, we assess which ingredients of the Coulomb stress change theory are decisive for explaining the succession of three large (Mw7+) earthquakes that occurred on a conjugate fault system in the NE Lut, East Iran, during a 30-year period. These earthquakes belong to a larger seismic sequence made up of 11 earthquakes (Mw5.9+) from 1936 to 1997. To reach our goal, we calculate, at each earthquake date, the stress changes generated by the static deformation of the preceding earthquakes, the following postseismic deformation due to the viscoelastic relaxation of the lithosphere, and the interseismic deformation since 1936. We first show that accurately modelling the source and receiver fault geometry is crucial to precisely estimating Coulomb stress changes. Then we show that 7 out of 10 earthquakes of the NE Lut sequence, considering the uncertainties, are favoured by the previous earthquakes. Furthermore, the last two M7+ earthquakes of the sequence (1979 and 1997) have mainly been favoured by the moderate Mw ∼ 6 earthquakes. Finally, we investigate the link between the Coulomb stress changes due to previous earthquakes and the rupture extension of the next earthquake and show that a correlation does exist for some earthquakes but is not systematic.

Exploring the Connection of XVI‐Century Major Historical Earthquakes in the Eastern Betic Cordillera, Spain: Insights From Viscoelastic Relaxation of the Lithosphere

“…A positive correlation between earthquakes and zones of positive static coseismic ΔCFS has been shown in multiple studies (e.g., Deng & Sykes, 1996; Harris & Simpson, 1992; King et al., 1994; Reasenberg & Simpson, 1992; Stein, 1999). In the past two decades, several authors have used the combined (static and viscoelastic) ΔCFS estimation to explore the interaction between earthquakes within complex fault systems in long‐term (e.g., Chëry et al., 2001; Freed et al., 2006; Liu et al., 2022; Marchandon et al., 2021; Rydelek & Sacks, 2001; Sunbul, 2019; Xiong et al., 2017). The combined ΔCFS expresses the effect of elastic rebound due to the static stress transfer and the viscoelastic relaxation in the less viscous lower crust and lithospheric mantle.…”