A COMPREHENSIVE DEFORMATION MODEL OF MAKRAN REGION, FOR SEISMIC HAZARD STUDIES

The Makran subduction zone is one of the last convergent margins that formed by the subduction of the Arabian plate beneath the southern coasts of Iran and Pakistan. The Makran convergence zone accommodates 3 cm/yr of convergence between Arabia and Eurasia. Despite this rapid relative plate motion, seismic activity in this region is low with only two significant historic earthquakes. The largest instrumentally recorded event is the 1945 Mw 8.1 Makran earthquake (Byrne et al., 1992); that shows the eastern Makran is locked and can produce large earthquakes. In contrast, the western Makran shows an almost total absence of shallow thrust earthquakes in both the instrumental and historical periods, with reports of only a single possible megathrust earthquake in 1483, for which the source region is poorly constrained (Musson, 2009). Therefore, we defined two models to evaluate the possibility of creep in the western part of Makran subduction zone. In the first model we assume that both part of Makran are temporarily locked (called the SDM); and the second model assumes the western Makran as a steady creeping subduction (called the HCDM). In this study, we combine three independent data sets (geologic slip rate, geodetic velocity, and principal stress direction) using a kinematic nite-element model, based on iterated weighted least squares fits to data, to better understand regional geodynamics of the Makran region. The newest regional joint solution of GPS data, azimuth of the most compressive principal stress, and geometry and kinematics of the potentially active faults mapped in prior geological studies, is included in the models. Model provides long-term fault slip rates, velocity, and distributed permanent strain rates between faults in the Makran region from all available kinematic data. This model allows us to better constrain the fault slip rates and distributed deformations and nally assess the seismic hazard and also can be used to produce longterm seismicity maps which are independent of historic and instrumental catalogs. The kinematic nite-element program (NeoKinema) was developed to combine all kinematic data including geological offset rates, GPS measurements, and principal stress directions by Bird and Liu (2007), which was used by Liu and Bird (2008); Khodaverdian et al. (2015) and UCERF3 (2013). The primary purpose of this modeling is to estimate long-term fault slip rates and distributed anelastic strain rates by combining all kinematic data including geological slip rates, geodetic velocities, and stress directions. The equations underlying the program are available from http://peterbird.name/oldFTP/NeoKinema. In the modeling program, the domain is divided into 2-D spherical-triangle nite elements (Kong and Bird, 1995).

Keywords:

Long-term slip rates , Makran , Subduction , Seismic hazard