Relative Structural Complexity of Plate Boundary Fault Systems Controls Incremental Slip-Rate Behavior of Major Strike-Slip Faults

Abstract:

A comparison of published incremental fault slip rates from four major strike-slip faults with the proximity and number of other active faults in the surrounding plate boundary system shows that the behavior of the master fault is strongly correlated with the structural complexity of its tectonic network. Specifically, the relative constancy of incremental slip rates along the San Andreas fault, the Alpine fault, the North Anatolian fault, and the Dead Sea fault reflects the proximity, number, and activity of their close neighbors. California’s San Andreas fault displays a steady incremental slip rate along its structurally isolated central section, whereas the Mojave section, located within a more complex surrounding fault network, has an irregular slip rate. Similarly, slip rates on the isolated south-central Alpine fault in New Zealand appear to be relatively constant through time, whereas to the northeast, where Alpine fault slip is transferred onto the four major strike-slip faults of the Marlborough fault system, incremental slip rates are highly variable. Incremental slip rates on the main strand of the North Anatolian fault are more constant along the structurally simple central part of the fault than on the multi-stranded western section. Finally, the Dead Sea fault exhibits more constant incremental slip rates along its structurally isolated southern section, relative to an irregular slip rate along its central section in Lebanon, where plate-boundary motions are accommodated on multiple sub-parallel faults. Based on these observations, we define a coefficient of complexity (CoCo) that quantifies the density and displacement rates of a master fault’s surrounding network. In each of the four systems, the CoCo correlates with the constancy or irregularity of the master fault’s incremental slip rate. We suggest that these behaviors are likely due to more complex stress interactions within more structurally complex regional fault systems, as well as possible kinematic interactions amongst mechanically complementary faults that collectively accommodate overall motion of the system. Our results provide a potential means for evaluating future behaviors of large plate-boundary faults and may improve the use of geological slip-rate data in probabilistic seismic hazard assessments.