Offshore mud volcanoes and onland faulting in southwestern Africa: neotectonic implications and constraints on the regional stress field

Microseismic Activity and Basement Controls on an Active Intraplate Strike‐Slip Fault, Ceres–Tulbagh, South Africa

“…Viola et al (2012) inferred southwest African stress evolution constrained by fracture systems and suggest a north-northwesttrending greatest horizontal stress for the most recent stress field along the coast of southwest Africa. Inland, the greatest horizontal stress appears to turn to a west-northwest-eastsoutheast trend (Viola et al, 2005;Bird et al, 2006). If we accept this stress field for the Ceres region, the subvertical microseismically active zone is relatively well oriented, but not ideal, for sinistral strike-slip faulting.…”

“…Stress measurements from borehole breakouts (Andreoli et al, 1996;Viola et al, 2005) and thin-shell rheological modeling (Bird et al, 2006) indicate that the southwestern coastal margin of South Africa experiences a northwestsoutheast-trending greatest horizontal stress. This stress direction is roughly parallel to the strike of the surface trace of the Ceres-Tulbagh microseismic zone reported here.…”

Seismicity and neotectonic uplift in the Augrabies Falls National Park, Namaqualand, Northern Cape, South Africa

“…Andreoli et al (1996) proposed neotectonic activity in South Africa to have been initiated in the Miocene (*25 Ma). The works of Andreoli et al (1996) as well as Viola et al (2005) highlighted that seismicity in southern Africa is driven by regional stresses originating from large-scale features that include intracontinental rifts, large-scale topographic elevations (such as the border of Lesotho and South Africa north of the Eastern Cape Province), and the network of mid-oceanic ridges. At present, neotectonics in southern Africa is increasingly associated with two large deviatoric stress fields: one with a predominant extensional NNE trend corresponding to the East Africa Rift System, and a second one, the Wegener Stress Anomaly (WSA) characterized by a NW-WNW compressive trend (Zoback et al 1989).…”

“…At present, neotectonics in southern Africa is increasingly associated with two large deviatoric stress fields: one with a predominant extensional NNE trend corresponding to the East Africa Rift System, and a second one, the Wegener Stress Anomaly (WSA) characterized by a NW-WNW compressive trend (Zoback et al 1989). According to Viola et al (2005), the Wegener Stress Anomaly is anomalous because the continental margin of the SE Atlantic should be of the passive margin and extensional type in terms of plate tectonics. Furthermore, the WSA is characterized by the Andersonian strike-slip fault regime (r 2 vertical, r 1 and r 3 horizontal).…”

Manual extraction of bedrock lineaments from high-resolution LiDAR data: methodological bias and human perception

“…They allow geological mapping in remote areas and over large spatial domains that are difficult or impossible to cover by foot, and permit easier recognition of regional patterns. Remote sensing in Earth sciences has been applied ever since aerial photographs became available and enjoys popularity due to readily available high quality satellite images, together with rapidly improving computing power, and is of great importance particularly in the field of brittle fracture analysis (e.g., Wise et al 1985;Lowman et al 1992;Viola et al 2005;Raharimahefa & Kusky 2009;Oden et al 2012;Awdal et al 2013). The high spatial resolution offered by Light Detection and Ranging (LiDAR) datasets, combined with the capability of scanning also through vegetation covers, has revolutionized the production of digital elevation models (DEM).…”