Subsurface structural mapping of Northern Nasser Lake region, Aswan, Egypt, using Bouguer data

Abstract

In this study, we attempt to delineate the subsurface structures for the
tectonic active region of Northern Nasser Lake using integrated interpretation techniques
of gravity data with seismicity. The depths to the gravity sources, and the locations of the
contacts of density contrast were estimated. Two methods were used for estimating source
depths and contact locations: horizontal gradient (HG) and Euler deconvolution methods.
Moreover, power spectral analysis, bandpass and upward continuation techniques were
applied to evaluate the shallow and deep seated structures. Shallow depth structures
were ranging between 0.30 km and 0.80 km. However, two average levels (interfaces) at
depth 3.1 km and 7.2 km below the measuring level were revealed for the intermediate
and deep seated structures respectively. Results of Euler deconvolution method suggested
that, in the eastern part of the area, the basement could be observed on the ground and has
become deeper in the central part. The interpreted structural map reveals that the area is
affected by a set of faults trending mainly in the NW, E–W, N–S and NE–SW directions.
Actually, this map has confirmed the idea that the intersections between the N–S and E–
W striking faults along Nasser Lake area have generated seismic pulses. Moreover, three
seismic zones (Z1, Z2 and Z3) are well correlated with the fault trends of the subsurface
structures as derived from the horizontal gradient map. The present results suggest that
there exist seismically-active fault east of High Dam, passing throughout Aswan reservoir
from north to south. This fault is occupying region of high stress values which may
generate large earthquakes in future, as it has long extension over several kilometers.
Furthermore, the evaluated intruded volcanic bodies are found almost at the intersections
between the E–W and NW oriented faults.