Active deformation in the Makran region using geological, geodetic and stress direction data sets

Abstract

SUMMARY Neotectonic flow of the Makran subduction zone is estimated using a kinematic modelling technique based on iterated weighted least-squares that fits to all kinematic data from both geological and geophysical sources. The kinematic data set includes 87 geodetic velocities, 1962 principal stress directions, 90 fault traces, 56 geological heave rates and velocity boundary conditions. Low seismicity of western Makran compared to its eastern part, may indicate that either the subduction interface is currently locked, accumulating elastic strain or aseismic slip (creep) occurs along this part of the plate boundary. Therefore, we define two different models to evaluate the possibility of creep in the western Makran. Models define a locked subduction zone versus a steady creeping subduction for the western Makran. The locking depth of the subducting fault is also investigated, and a locking between 14 and 40–45 km depth provided the best consistency with geodetic observations. The 2 kinematic models provide long-term fault slip rates. The models estimated the shortening rate of 16.6–22.5 mm yr−1 and the strike-slip movement of 0.2–6.0 mm yr−1 for six segments along the subduction fault. The steady creeping subduction model predicts a 1–2 mm yr−1 lower shortening rate than the locked model for the Makran subduction fault (MSF). To verify the results, the estimated fault slip rates are compared to slip rates based on the geodetical and geological studies, which have not been used as model inputs. Our estimated rates fall within the range of geodetic rates and are even more consistent with geological rates than previous GPS-based estimates. In addition, the model provides the long-term velocity, and distributed permanent strain rates in the region. Based on the SHIFT hypotheses, long-term seismicity rates are computed for both models based on the estimated strain rate. These maps were compared with seismic catalogues. The estimated seismicity rate for the western part of Makran from the creeping subduction model is more compatible with the observation. The results of two deformation models lead us to a coupling ratio of ∼0.1 for the western MSF.