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