Characterising the contemporary stress orientations near an active continental rifting zone: A case study from the Moatize Basin, central Mozambique

Abstract

This paper presents the first comprehensive analysis of the present-day stress from boreholes near an active continental rifting zone in the Moatize Basin, Mozambique.The state of present-day stress in this area that is located ca. 100 km away from the Eastern African Rift System (EARS) is poorly understood, and most of our knowledge is from earthquake focal mechanisms that provide stress information from the deeper part of the lithosphere, and to a lesser extent from surface geological features in the Malawi region. Considering the limited reliability of earthquake-derived stress orientations near plate boundaries, poor coverage of low to moderate magnitude earthquakes in eastern Africa, and ambiguity about the latest activity of geological structure; other well-established methods are required to shed light on the active tectonics of EARS. In this study, we analyse stress orientation using log data from 95 vertical boreholes in a mine site to investigate the neotectonic stress pattern of the region. Analysis of 17.9 km of televiewer logs resulted in interpretation of 1188 stress-related borehole failures.The results indicate a mean regional trend of 045° ± 31° for the maximum horizontal stress (S Hmax ). Our investigation reveals that the regional state of stress in the study area is controlled by superposition of stress sources that act at very different spatial scales. The consistency between our results and predictions by plate-scale geodynamic models of stress orientations confirm that the regional pattern of stress in this area is mainly controlled by first (>500 km) and second (distances between 500 and 100 km) order stress sources (i.e., large tectonic forces and lateral density variations). However, high-resolution data used in this study reveal that third (between 100 and 1 km) and fourth (<1 km) order stress sources from stiffness contrasts, rock fabric and geological structures have a great impact on the stress perturbations at smaller and local scales.

Fault controlled geometries by inherited tectonic texture at the southern end of the East African Rift System in the Makgadikgadi Basin, northeastern Botswana

“…1). Although one sees strain rotations across distances o <100 km in East Arica (Morely, 2010;Rajabi et al, 2022;Williams et al, 2019), the available data nevertheless suggests that in the bigger picture, signifcant strain rotation (i.e. nearly 180 • rotation) within the San Plate exists.…”

The effect of stiffness contrasts at faults on stress orientation

“…Over the last decade, a great increase in high-resolution image logs in various basins across the world, provides the opportunity for detailed observation of such small-scale stress rotations in the vicinity of faults at borehole scales (Lin et al, 2010;Rajabi et al, 2022Rajabi et al, , 2024Sahara et al, 2014;Talukdar et al, 2022;Zhang et al, 2023). Figure 1a shows an example of stress reorientation of approximately 90 • indicated by borehole breakouts (Bell and Gough, 1979;Heidbach et al, 2018) in the vicinity of and attributed to a fault, which has been interpreted in an electrical image log in the Surat Basin of Queensland, Australia (Rajabi et al, 2017a).…”