Seismic refraction survey to investigate shallow sediments of Wadi Thuwal, North of Jeddah, KSA

الملخص EN

A seismic refraction survey was conducted along 32 seismic profiles, to study the near-surface sediments and to delineate the level of the water table in Wadi Thuwal area, which is located 110 km to the north of Jeddah, KSA.

Processing and interpretation of seismic data established a 2D-geo-seismic model consisting mainly of three layers: a surface wadi fill layer (sand and silt) with low average seismic velocity of 420 m / s, dry to water-saturated sand, clay and conglomerate with moderate average velocity of 1150 m / s, and a reefal limestone bedrock with high average velocity of 2710 m / s.

Seismic velocities (V) of the delineated seismic layers were analyzed.

Consequently, a linear relationship between seismic velocities and depth (Z = 2.134 - 0.0085 V) was found, suggesting that there exists of a uniform seismic gradient across these seismic layers.

A zone of lower bedrock velocity (1700 m / s) was outlined at the eastern part of the study area, adjacent to Harrat Thuwal, indicating a highly weathered fractured limestone.

There is a gradual increase in the bedrock seismic velocity and depth from east to west and to north.

Published velocity-rippability relations were used to confirm that the bedrock of the western part of the area would require blasting for excavation.

It was difficult to determine water table depth because the high bedrock seismic velocity has, in some localities, masked the signature of the relatively lower seismic velocity indicative to the water table.