Localized versus distributed shear in transform plate boundary zones: The case of the Dead Sea Transform in the Jericho Valley

Abstract

Continental transform plate boundaries are typically either localized along a single, usually segmented, major fault or distributed over a broad deformation zone. In the latter, shear is partitioned between major strike slip faults and intervening, often rotating, fault systems. Analog and numerical simulations suggest that such internal fault systems evolve and may be localized or delocalized depending on strain and fault zone strength. This paper examines the degree and evolution of shear localization in the Jericho Valley section of the Dead Sea Transform (DST), which is part of the Africa/Arabia plate boundary. In this section, the current breadth of the transform valley and its penetrative strain field are difficult to reconcile with localized shear. We integrate newly acquired high‐resolution reflection data, reprocessed exploration reflection data (both focused to 2.5–3.5 km depth), relatively relocated earthquake epicenters, and fault plane solutions based on P wave first arrivals and suggest reinterpretations for previously published structural and seismic data in the Jericho Valley and the northern Dead Sea basin. It is found that shear in this section of the DST evolved from an early, probably Miocene‐Pliocene, stage of localized strike slip motion primarily along the Jericho fault to a late stage (Pliocene‐Recent) when shear has been distributed over internal fault sets that apparently lean against a major eastern DST segment. In the early stage the Jericho fault formed the western boundary of a deep, narrow, probably pull‐apart basin filled by fluvial clastics and evaporites. This is overlain by the late stage broad basin, characterized by low‐energy deposition of lacustrine and fluvial sediments. Pliocene rock salt has apparently utilized the Jericho fault zone as a conduit for diapirism, causing the uplift, normal faulting, and surface deformation of Late Pleistocene and Holocene sediments currently observed along the ∼15 km long Jericho Lineament. On the basis of the currently observed dextral‐normal motion across the internal NNE‐NE trending fault system, counterclockwise rotation is expected to have occurred within the transform zone. These tectonic and depositional changes were probably associated with onset of transtension across the DST, related to the previously postulated shift of the Africa/Arabia Euler pole of rotation in the Pliocene.