Field examples of strike-slip fault terminations in Mongolia and their tectonic significance

Deformation at the ends of large intracontinental strike-slip faults that do not simply link other major structures often involves rotations about a vertical axis. We use earthquake slip vectors, surface rupture in earthquakes, and geomorphology to examine the ends of three major strike-slip faults in Mongolia. In these places a simple pattern is seen, consisting of a thrust fault on one side, with a displacement that decreases away from the strike-slip fault, consistent with local rotational deformation. Strike-slip faults that terminate in this way allow the style of faulting to change spatially within a deforming area, for example, from dominantly strike-slip to dominantly dip-slip, while still accommodating the overall deformation required by larger-scale regional motions. Such a change in fault style should also be accompanied by a change in the rotation rate about a vertical axis, which may be detected paleomagnetically. The kind of strike-slip fault termination described here may have consequences for how large strike-slip faults evolve and grow and for the variation in displacement along their length.