Depth estimates of anomalous subsurface sources using 2D/3D modeling of potential field data: implications for groundwater dynamics in the Ziway-Shala Lakes Basin, Central Main Ethiopian Rift

Abstract

Quantitative analysis of potential field data are made in the Ziway-Shala lakes basin over an area bounded by 38 ° 00′ E - 39 ° 30′ E and 7 ° 00′ N - 8 ° 30’ N. Most previous geophysical studies in the region under consideration focus on mapping the deep crustal structures and undulation of the Moho depth. Only few studies are targeted at mapping the shallow subsurface structures. The main focus of this paper is mapping geometries of the major lithological and structural units of the shallow subsurface using gravity and magnetic data. The ultimate objective of the research is to understand the hydrogeological dynamics of the region through mapping interfaces geometries. Automatic inversions, 2D joint forward modeling and 3D inversion are the major techniques employed. The 2D Werner de-convolution based on both gravity and magnetic data along the rift axis showed source depths tending to deepen northwards. Source depths estimates determined by Source Parameter Imaging also showed similar tendency. This is further strengthened by the joint 2D forward modeling of gravity and magnetic data which showed the top of the basement is sloping northwards. The result of the 3D gravity interface inversion agrees with results of the above mentioned depth estimation techniques. Finally, the gravity power spectral analysis resulted in two depth estimates, 1.53 km and 2.87 km which approximate the positions of two density interfaces. The shallow depth interface is thought to presumably delineate the low density Fluvio-lacustrine sediments including the rift floor volcanic units and crystalline basement. Our investigation results agree with the results of previous seismic studies which identified low velocity (“sediment-volcanic”) horizon in the rift floor with low resolution. The information obtained with regard to water balance of the basin, salinity level of the lakes and the conceptual hydrological flow model appears to reveal that the groundwater flow in the study region is controlled by subsurface structures, particularly, the mapped interface topographies.

Determination of Conrad and Curie point depth relationship with the variations in lithospheric structure, geothermal gradient and heat flow beneath the central main Ethiopian rift

“…A total of about 2335 secondary including primary total magnetic intensity (TMI) data are used to compute the CPD beneath the central MER and surrounding regions. The secondary TMI data were obtained from MSc works of numerous scholars (Kebede, 2014; Berhane 2015 ; Kelemework, 2016 ; Nigussie, 2020 ) and Kebede et al. (2021) guided by their advisor Dr. Abera Alemu.…”

Structural interpretation of Southern Main Ethiopian Rift basin using constrained full tensor gravity inversion of the basement morphology

“…Field studies showed that in some localities of Amaro Horst crystalline basement is unconformably overlain by Pre-Tertiary or Mesozoic sedimentary rocks possibly extend into studied sub-basins with larger thickness than the elevated area where the unit is exposed. Multi-Layer 3D gravity forward modeling in northern parts of Ethiopia by Mammo (2010) and 2D/3D modeling of potential field data in Central MER by Kebede et al. (2021) shows that the existence of Mesozoic sediment overlaid on the Precambrian basement rock.…”

Unraveling the Geothermal Potential of Corbetti Caldera using Integrated Geophysical Methods, Central Main Ethiopian Rift

“…The NNE-SSW trending regional rift forming faults are also observed on Southern MER (B. Kebede & Mammo, 2021;H. Kebede et al, 2021).…”