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Radar interferometric measurements of current deformation along the southern Dead Sea Transform: tectonic and geotechnical implications

Gidon Baer(1) and Yoseph Yechieli(1)

(1) Geological Survey of Israel, 30, Malkhe Yisrael St.,, 95501, Jerusalem, Israel

Abstract

Interferometric Synthetic Aperture Radar (InSAR) measurements along the southern part of the Dead Sea Transform (DST) reveal surface deformation of both tectonic and geotechnical significance. About 140 ERS-SAR scenes were processed, covering a region of about 500x150 km2, from the southern part of the Gulf of Elat to the Jordan Valley; interferograms were made for 11 year period (1992 2003). The November 22, 1995, Nuweiba earthquake is the major seismic event during this period. Comparison between coseismic and model interferograms, indicate 1.4 - 3 m slip on a rupture plane buried 0 - 4 km below the Gulf bottom, respectively. Phase gradient maps of the coseismic deformation indicate triggered slip on sub-parallel and oblique faults near the termination of the main rupture. Postseismic deformation following the Nuweiba earthquake is restricted to the first 6 months after the earthquake, and it is most likely associated with aftershocks along a Gulf-parallel normal fault. The postseismic deformation may be the mechanism of Gulf deepening, as similar faults are observed in young sediments on shore. InSAR-detected deformation in the Arava segment of the DST, 100 - 200 km north of the 1995 epicenter, include displacements at small (a few km long) extensional basins and compressional ridges associated with releasing and restraining fault bends, respectively. In some cases these displacements are episodic. We modeled the displacements as creep events at the stepover zones. The moment release by this creep in the Arava segment accounts for as much as 50-75% of the total expected moment (for assumed slip rate of 1.5 mm/yr along the entire DST), whereas the seismic efficiency is less than 1%. Spatial association is observed between creep events and increase of local seismicity.

Ground subsidence has been measured along a significant length of the Dead Sea shorelines. It is attributed to the consolidation of fine- grained marly layers due to water level drop. The subsiding areas and associated sinkholes display linear patterns that are most likely controlled by active faults. The relationships between gradual subsidence features and sinkholes are used for hazard maps. We also examined the case of a dam constructed in 1999 along a new salt evaporation pond in the Lisan Peninsula (Dead Sea) that collapsed 4 months after completion. It seems possible that the collapse of the dam was linked to previous gradual subsidence that we detected by InSAR analysis. Finally, the salt diapir of Mount Sedom (southwestern Dead Sea) is continuously rising at a rate of 6-8 mm/yr, in agreement with the known Pleistocene-Holocene uplift rate. The Lisan Peninsula diapir, on the other hand, does not rise at a measurable rate.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry