Microgravity Survey to Evaluate Earthquake Effects on the Derbendikhan Dam Site, Iraq

Abstract

ABSTRACT A microgravity investigation was conducted along the axis of the Derbendikhan rockfill dam in Iraq. The dam lies in an earthquake-prone area within the High Folded Zone of the Western Zagros Fold–Thrust Belt. The goal of the survey was to evaluate the expected subsurface damage that could threaten the stability of the dam due to the effects of a 7.3 magnitude earthquake and future earthquakes that cause foundation cracking and landslides. The survey consists of 324 microgravity stations distributed on four profiles. Residual gravity anomalies were obtained by removing the regional effect of a 5-m upward continuation filter. Several negative and positive anomalies are distinguishable in a residual anomalies map that reflects the subsurface heterogeneity within the clay material that makes up the dam. The results reveal that there are no recognizable indications regarding the evolution of subsurface channels after the earthquake was given. Furthermore, two prominent anomalies appear close to the right bank at roughly 21 m in depth. These positive and negative anomalies suggest that high- and low-density zones coincide with different degrees of compressional stresses caused by the earthquake. Two-dimensional modeling indicates several low (less compacted) and high (more compacted) density areas that warrant further investigation in terms of material strength. The results can be used as a guide for a drilling program to examine the sources of the anomalies.