The stepovers of the Central Dead Sea Fault: What can we learn from the confining vertical axis rotations?

Abstract

The geometry of stepovers along strike-slip faults dictates the deformational field and topography induced around the faults. Stepover geometry also impacts the ability of a fault rupture to propagate from one fault segment to another and therefore acts as a major controlling factor in the size of earthquakes. However, the geometry of stepovers is often poorly resolved, as they tend to underlie young sedimentary successions. Yet, although mostly ignored, the accumulated long-term relative plate motions accommodated by the stepping faults generate permanent rotational deformation in the crust surrounding them. Here we present the results from a combined mechanical and paleomagnetic investigation of the vertical axis rotational pattern confining stepovers. We focus our investigation on the central Dead Sea Fault, where two prominent stepovers are located at the Kinneret and Hula depressions. To better understand their still somewhat elusive geometric settings, we mapped the crustal rotational field by studying the magnetization of the confining volcanic rocks. Remanent magnetization directions reveal localized zones of anomalously high vertical axis rotations in the vicinity of the stepovers that evolve to negligible rotations elsewhere. We then constructed a series of elastic and elasto-plastic slip models aiming to cover possible plate boundary architectures. Comparable patterns between the observed and predicted rotations were achieved when the Dead Sea Fault motion was concentrated along the eastern margins of both the Kinneret and Hula Basins. Our best-fit model suggests that the along-strike under-lapping distance for the Kinneret Stepover is ~8 km whereas for the Hula Stepover is only ~2 km. Our results, supported by historic and paleoseismic records that show no evidence of an earthquake that ruptured through the Kinneret Stepover, imply an enhanced deformation zone in the center of Lake Kinneret, which acts as a major barrier to rupture propagation. Our combined paleomagnetic and modeling analysis approach provides a new avenue for the study of the geometries of plate boundaries.