Chapter 11 - Spatial and Temporal Distributions of Deformation in Strike-Slip Faults: The Karakoram Fault in the India-Asia Collision Zone

Abstract

Assessments of spatial and temporal distributions of deformation within fault zones, including their ductile shear zones, are critical for characterizing wider deformation of the lithosphere and associated seismic hazard. However, deformation within fault zones, often quantified as slip rate or strain rate, is potentially heterogeneous in any of the three spatial dimensions (i.e., along strike, across strike, and with depth) and in time. The complex distributions of deformation that result present a challenge for assessments of the present and past behavior of individual faults and for establishing models of the roles of faults in deforming regions. In this review, we present a case study of the strike-slip Karakoram fault zone (KFZ) in the India-Asia collision zone to summarize evidence for the spatial and temporal distributions of deformation within the fault zone and highlight the challenges that heterogeneous deformation presents for constructing models of fault behavior at the present day and during the history of a deforming region. The KFZ provides an ideal case study because its fault rocks are exhumed and well exposed, and due to its key location within the collision zone. Geological, geomorphological, and geodetic observations constrain the behavior of the fault during the Neogene, Quaternary, and present day. Since initiating at ~15Ma, the KFZ has accumulated strike-slip offsets that vary along its length from ~52 to ~150km. Offset Quaternary landforms indicate spatial (along and across strike) and temporal heterogeneities in slip rate of several mmyr−1. The upper-crustal portion of the fault generates large earthquakes with recurrence intervals of at least several hundred years, whereas deformation in the mid-crust is aseismic, ductile, and more broadly distributed. The KFZ offers a potential analog for other major strike-slip faults for which portions of this record (in space and/or time) may not be accessible.