Abstract
A new geophysical methodology for sinkhole hazard assessment is under development in the framework of Project M27-050 granted by the MERC Program (USA). The key point of the new methodology is delineating salt distribution, in particular the salt edge, based on the timedomain electro magnetic method. We consider a new approach to use the Transient Electromagnetic (TEM) method in its FAST modification for studying the distribution of bulk resistivity in the vicinity of the salt edge and the salt layer properties: porosity, depth and thickness.
After locating the salt layer edge we can separate the area into two territories of investigation: 1 “salt” area, where the measured resistivity is influences by the salt porosity (based on Archie’s law). (2) “no-salt” area, where the measured resistivity is influences by groundwater salinity based on resistivity-salinity calibrations generated for the Dead Sea region.
The new methodology permits also 2D and 3D presentation of the acquired results despite the fact that data are acquired in 1D. With this kind of interpretation we applied the TEM FAST methodology to investigate salt conditions through the Shalem-2 (Mineral) site. The methodology includes fast spacious mapping of the bulk resistivity in both vertical and
horizontal directions through the area covering ~1 km2.
The results in the “salt area” characterize three zones bases on their resistivity, the zones are
with good correlation with the distance from the Dead Sea shore:
1. Resistivity up to 0.5 Ohm-m: Found far from the Dead Sea, near the salt edge. The zone is not
regular and is associated with a salt karst. Sinkhole formation in these zones is most probable.
2. Resistivity of 0.5-1 Ohm-m: Intermediate zone with increased porosity.
3. Resistivity of more then 1 Ohm-m: Found close to the shore, this is the background porosity.
Estimation of the salt porosity can be based on calibration of the resistivity that will be carried out in the future. The map of the salt top surface shows deepest position in the central part of the area (-434 m sub sea) and it becomes shallower at the margins of the studied area (-424 m).
Mapping the “no-salt area” shows the high relative resistively of the clastic sediments (0.6-0.75 Ohm-m) along the salt edge. Such resistivity can characterize the saline with chloride concentration of 60-100 g/l compare to 224 g/l at saturation. Additional method of seismic refraction and drill borehole will add in the future for better
calibration.
After locating the salt layer edge we can separate the area into two territories of investigation: 1 “salt” area, where the measured resistivity is influences by the salt porosity (based on Archie’s law). (2) “no-salt” area, where the measured resistivity is influences by groundwater salinity based on resistivity-salinity calibrations generated for the Dead Sea region.
The new methodology permits also 2D and 3D presentation of the acquired results despite the fact that data are acquired in 1D. With this kind of interpretation we applied the TEM FAST methodology to investigate salt conditions through the Shalem-2 (Mineral) site. The methodology includes fast spacious mapping of the bulk resistivity in both vertical and
horizontal directions through the area covering ~1 km2.
The results in the “salt area” characterize three zones bases on their resistivity, the zones are
with good correlation with the distance from the Dead Sea shore:
1. Resistivity up to 0.5 Ohm-m: Found far from the Dead Sea, near the salt edge. The zone is not
regular and is associated with a salt karst. Sinkhole formation in these zones is most probable.
2. Resistivity of 0.5-1 Ohm-m: Intermediate zone with increased porosity.
3. Resistivity of more then 1 Ohm-m: Found close to the shore, this is the background porosity.
Estimation of the salt porosity can be based on calibration of the resistivity that will be carried out in the future. The map of the salt top surface shows deepest position in the central part of the area (-434 m sub sea) and it becomes shallower at the margins of the studied area (-424 m).
Mapping the “no-salt area” shows the high relative resistively of the clastic sediments (0.6-0.75 Ohm-m) along the salt edge. Such resistivity can characterize the saline with chloride concentration of 60-100 g/l compare to 224 g/l at saturation. Additional method of seismic refraction and drill borehole will add in the future for better
calibration.
| Original language | English |
|---|---|
| Pages | 100-100 |
| Number of pages | 1 |
| State | Published - 2011 |
| Event | Israel Geological Society, Mitzpe Ramon, 2011 - Mitzpe Ramon, Israel Duration: 22 Mar 2011 → 24 Mar 2011 |
Conference
| Conference | Israel Geological Society, Mitzpe Ramon, 2011 |
|---|---|
| Country/Territory | Israel |
| City | Mitzpe Ramon |
| Period | 22/03/11 → 24/03/11 |