Geophysical prediction and following development sinkholes in two Dead Sea areas, Israel and Jordan

摘要

Geophysical methods-seismic refraction (SRFR), electrical resistivity tomography (ERT), and microgravity-were applied to the Dead Sea (DS) sinkhole problem in the Ein Gedi area at the earlier stage of the sinkhole development (1998-2002). They allowed determining the sinkhole formation mechanism and localizing the sinkhole hazardous zones. The SRFR method permitted to delineate the underground edge of a salt layer at the depth of 50 m. The salt edge was shaped like the sinkhole line on the surface. It was concluded that the sinkhole development is linked to the salt edge. Geoelectrical quasi-3D mapping based on the ERT technique detected large resistivity anomalies with 250-300 m~2 diameter and 25-35 m deep. The Ein Gedi area has been also mapped by the use of Microgravity method. The residual Bouguer gravity anomaly map shows negative anomalies arranged along the edge of the salt layer. Those gravity anomalies overall are very similar in plan to the resistivity distribution in this area. The results of forward modeling indicate that both high resistivity and residual gravity anomalies are associated with a subsurface decompaction of the soil mass and deep cavity at the sinkhole site. Following monitoring of the sinkhole development carried out by the Geological Survey of Israel confirmed our suggestions. The drilling of numerous boreholes verified the location of the salt edge. Geographical Information System (GIS) database testifies that during 2003-2009 new sinkholes are continuing to develop along the salt edge within a narrow 50-100 m wide strip oriented approximately in north-south direction (slightly parallel to the shoreline). No promotion in west-east direction (perpendicularly to the DS shoreline) was observed in Israel. Collapse of sinkholes and their clustering have been occurred within the area of high resistivity anomaly and negative residual gravity anomaly. Similar studies carried out at the Ghor Al-Haditha area (Jordan) have shown that sinkholes there are also arranged along the winding line conforming to the salt edge. In this area sinkholes are slowly moved to the Dead Sea direction. Results of geophysical studies in numerous DS sites indicate similar sinkhole development. It allowed generating of the sinkhole formation model based on ancient (10,000-11,000-year old) salt belt girding the Dead Sea along its shores.