Detecting and modelling the collapsed zone around a shaft in a dam site by microgravity data.

The low-density regions caused by collapsed zones can be delineated and modelled in dam sites by microgravity data. After measuring the data and using standard correction methods, the Bouguer anomalies are computed. The residual anomalies are obtained by removing the trend or regional anomalies from Bouguer anomalies. The negative anomalies, which are caused by low-density zones, can be readily distinguished in a residual anomaly map. Detecting and modelling these zones could prove a difficult task in dam sites due to the likely rough topography and construction activities in and around the sites. A collapsed zone in and around a shaft is detected and modelled in the Siah-Bisheh dam site in the Alborz Mountains in northern Iran. [ABSTRACT FROM AUTHOR]