Seismicity around the boundary between eastern and western Makran

Abstract

The Makran subduction zone is segmented into western and eastern parts. The small number of teleseismic and regionally-recorded earthquakes makes it difficult to detect possible seismic activity along the border between eastern and western Makran. Additionally, the scarce seismicity does not allow us to investigate seismic deformation of the fore-arc Jazmurian Depression and the Sistan Suture Zone, understand the relationship between the intermediate-depth seismicity and the subducting plate, and estimate the seismic moment release in Makran. To address these questions, we installed a temporary seismic network of 39 stations around the border between eastern and western Makran from June 2016 to November 2019. The observed seismicity shows a NNW-SSE trending alignment of shallow small-magnitude earthquakes within the northern part of the accretionary prism along the longitude of ∼ 60°. Earthquakes are more frequent to the east of the trend, implying the trend may be associated with the approximate boundary between western and eastern Makran. The new seismicity map shows that the Jazmurian Depression is surrounded by shallow crustal earthquakes, suggesting that it is an aseismic block. Scattered shallow seismicity is also observed within the Sistan Suture Zone, but seismicity is more concentrated along its border with the Lut block, which indicates a relative motion between them. We show that the intermediate-depth earthquakes occur within the subducting plate, and the rate of seismic moment release in the Makran megathrust zone is much less than those of the Alaska, Nankai, Chile, Kuril, and Mexico megathrust zones.