Seismological and GPS constraints on Sinai sub-plate motion along the Suez rift

Abstract

This work presents new seismological and Global Positioning System (GPS) results aimed at understanding the nature and rate of strain associated with the opening of the Suez rift that separates the Sinai sub-plate from the African plate. The Sinai sub-plate has played a significant role in the tectonic evolution of the northern Red Sea and the Eastern Mediterranean region. Most small, moderate and large earthquakes occur within belts associated with the geologically documented borders of this sub-plate including the Dead Sea fault (DSF) system in the east, the Cyprian arc (CA) in the north, and the Suez rift (SR) to the southwest. The DSF and CA are well defined; however, the SR is only partially defined. Earthquake foci distribution supports the idea that the SR is seismically active, and this earthquake activity cannot be ignored throughout the kinematics evaluation of northern Red Sea region. The earthquake activity is relatively higher in the southern part of the SR and gradually decreases northward. The high seismicity is mainly attributed to the presence of the Sinai triple junction. Earthquake focal mechanisms in the SR are dominated by oblique normal faulting with left-lateral strike-slip components on NW trending fault planes consistent with regional kinematics. The extensional semi-principal stress axes derived from fault plane solutions are oriented NNE-SSW in good agreement with the current stress field obtained from borehole breakouts along the SR as well as results from GPS surveying. Recent survey-mode GPS observations provide evidence for coherent northerly motion of the Sinai sub-plate that varies between 2 and 5 mm/yr. Moreover, strain analysis indicates that the southern SR is dominated by extension while its northern segment is characterized by constriction, inconsistent with earthquake focal mechanisms and regional tectonic models. The overall northward motion of the Sinai sub-plate indicates that slab-pull rather than ridge-push is the dominant force controlling regional kinematics. Based on the low rate of extension and lack of oceanic crust, the SR can be considered an incipient plate boundary between the Sinai sub-plate and the Nubian plate.