Why does western Makran have a low seismicity rate?

The Makran Subduction Zone is segmented into western and eastern Makran where all instrumentally recorded megathrust earthquakes happened in eastern Makran. To find out how the lack of megathrust earthquakes and the observed low seismicity rate in western Makran is related to a combination of long interseismic quiescence, aseismic creep, or low rate of interseismic strain accumulation within the megathrust zone, we have complemented the five existing GPS vectors along the coasts of Makran by nine new GPS vectors and an extra eight new GPS vectors across the width of the Makran megathrust zone. Our block modeling shows that the coupling of the subducting Arabian oceanic plate with the overriding plate in western Makran is more than four times smaller than that of eastern Makran. Additionally, the maximum interseismic strain rate accumulation within the onshore part of the megathrust zone of western Makran is >7 times smaller than that in eastern Makran. We found a right-lateral motion of about similar to 16 mm across the transfer zone between Zagros and Makran. We consider a much lower earthquake hazard for western Makran relative to that of eastern Makran because the overriding Lut block is moving northward causing much less strain accumulation within the megathrust zone, and because of the lower seismic coupling between the subducting and overriding plates. Our findings show a large strain rate across the transfer zone between Zagros and Makran and thus imply a much higher earthquake hazard for the transfer zone.

Automated summary

The Makran Subduction Zone is divided into western and eastern regions, with the majority of megathrust earthquakes occurring in the eastern region. This study investigates why the western region experiences a lack of megathrust earthquakes and lower seismicity rate compared to the eastern region. By analyzing GPS data, the researchers found that the coupling between the subducting Arabian oceanic plate and the overriding plate in the western region is significantly weaker than in the eastern region. Furthermore, the rate of strain accumulation within the megathrust zone in the western region is much smaller than in the eastern region. The study also reveals a right-lateral motion across the transition zone between the Zagros and Makran. These findings suggest a lower earthquake hazard in the western Makran due to the northward movement of the overriding Lut block and the reduced seismic coupling between the subducting and overriding plates, while indicating a higher earthquake hazard in the transition zone between the Zagros and Makran.