Multi-temporal interferometric approaches to detect surface deformation in Dessie basin, Ethiopia

Abstract:

Slope instability problems in the Dessie basin, Ethiopia, has been known for almost half a century. The consequences of surface displacements also significantly affect the socio-economic condition of the Dessie basin, one of the many hanging tectonic structures situated laterally at the western Afar escarpment. However, this continuous natural geo-hazard remains a limited understanding of the different positive and negative feedback or factors that control it. Geologically, a sequence of Tertiary Trap Series, which is highly weathered and densely jointed basaltic rock, inter-bedded with weakly degraded volcanic units and several reddish paleosoil horizons are exposed as major bedrocks. Additionally, the basin floor is predominately filled with Sediments of colluvial-alluvial deposits. These highly weathered rocks associated with unconsolidated materials in steep slope serve as significant factors for slope instability. This paper investigates slope instability in the Dessie basin using the Sentinel-1 image extended from 2014 to 2020. Also, we spatially compare the location of ground displacement with high spatial-resolution optical satellite imagery (41 cm) and from Lidar at 10 m resolution. We employed the two currently available multi-temporal interferometric approaches: Small Baseline Subset (SBAS) and Permanent Scatterers interferometric (PSI). These two different and cost-effective time-series algorithms help us to understand better the influence of tectonic and seasonal factors that control the slope instability of the area since both capable of producing displacement time series data set. The detected surface motion was dominated by the subsidence caused by debris/earth slides, debris/earth flows, and medium to large-scale rock-slides by a line of sight displacement rate (LOS). Furthermore, the time series results from both PSI and SBAS revealed a bimodal distribution per year, which correlates well with the rainy season of the basin, indicating heavy rainfalls might have been playing a significant role in triggered slope instability in addition to other anthropogenic effects.