A Kinematic and Morphometric Analysis of Restraining Bends in the Eastern California Shear Zone

Restraining bends are concentrated areas of uplift and deformation due to compressional jogs along strike-slip faults. Although previous experimental and field investigations have provided insights into the development of bends as well as their important influence on topography and complex controls of earthquake rupture dynamics, it is not clear what drives bend initiation and subsequent longevity (i.e., changing plate boundary conditions or development of an immature fault system). Reconstructions of early-stage kinematics of real-world restraining bends are key steps to addressing these issues but are rarely possible, because they are transient features that are abandoned, cannibalized, and eroded over time. In the south Mojave block of the Eastern California shear zone (ECSZ), restraining bends from a range of developmental stages occur due to progressive transpression on right-lateral faults with relatively low net-slip (e.g., Emerson, Calico, Lenwood, Johnson Valley). Using field-based neotectonic maps, morphometric analyses, and numerical modeling, we investigate a uniquely suited array of evolving restraining bends (n≈15) to examine how their kinematic and topographic evolution relates to varying slip-rates, primary fault trends, and regional plate motion. The km-scale bends are generally doubly-fault bound and have an arrowhead shape in planview with asymmetric positive flower structures of basement cores and plunging anticlines of overlying folded sediments. The tops of the bends are relatively flat with relict granitic erosion surfaces that constrain vertical displacement patterns. They also exhibit self-similar forms with ~3:1 length-to-width ratio and relief that scales with length. The similarities persist across simple double bends on individual faults, bends developed at the confluence of primary faults, and in poly-deformed wedges dissected by multiple faults. We are further testing the mechanics that drive the similar manifestation of transpression across different conditions using numerical 3D deformation models. Our preliminary results indicate that transpressive deformation in the southern ECSZ is largely characterized by continuous geometric rearrangement, leading to bend growth, migration, and uplift.