DETECTION OF NEOTECTONIC FEATURES COMBINING ADVANCED REMOTE SENSING DATA, THE CASE STUDY OF THE DEAD SEA RIFT, SOUTHERN ISRAEL

Shimoni Michal (Ph.D. student)

Department of Applied Earth Sciences

Section Earth Sciences

The objective of this research is to show that combining optical data, physical features extracted from radar data and geophysical information can improve the understanding of tectonic processes in rift areas. By using new analysis techniques and geophysical inversion models the research will extract quantitative information about surface mineralogy from the optical data. SAR Interferometry will provide relative measures in the order of a few centimetres or even less for movement in the vertical direction.The combination of data from optical (DAIS-7915) and microwave (ERS-1/2) remote sensing instruments will be used to produce a model to detect minor faults caused by neotectonic processes in the Dead Sea Rift, southern basin, Israel.

Introduction

The ERS-1/2 tandem mission opened a new dimension in geology and tectonic research. Displacements of active tectonic structures can be detected by using the phase of the radar signal. However, the global understanding of neotectonic process, as well as interpretation of the interferometry data, require geophysical investigation and complete description of the geological setting. Regional geological mapping and mineral exploration are within the main targets of hyperspectral technology. In areas were faults are covered by loose sediments, the surface mineralogy deposition is essential. The majorities of movements along the “Southern basin” Dead Sea rift are not sensational, but are nevertheless important for long-term understanding of its origin and its activity.

A thick (>2000 m) sequence of mostly marine salt with inter-bedded gypsum, shale and dolomite rock of Pliocene to Pleistocene age build several salt diapirs in the Dead Sea area. In mount Sedom the diapir is exposed at the surface. Other diapirs (e.g. Lisan Peninsula, En Gedi) are buried at varying depths (in places only a hundred meters) below the surface. This report presents some preliminary results of combining seismic and advanced differential interferogram processing of the Lisan Peninsula.

This research project started in December 1999 and it is due to finish in April 2003

Results in 2000

Uplift rates for some of the Dead Sea diapirs were calculated using geological observations. The geological uplift rates for Mt. Sedom are between 3.5 and 10 mm/year, whereas the calculated uplift rate of the Lisan diapir is 1-2 mm/year. The region along the western shores of the Dead Sea and the Lisan peninsula were chosen for detailed interferometric analyses of uplift and subsidence.

The Lisan Peninsula (Figure 1), consists mostly of late Pleistocene Lisan Formation, overlying a salt diapir, and is overlaid at the margins of the peninsula by the Holocene Ze’elim Formation. The salt diapir is elongated in the N-S direction, and includes several sub-domes and a structural depression. Folds in the Lisan formation layers above the diapir delineate the structures of the sub-domes. Two faults, striking N-S and NE, bound the peninsula in the east and northwest, respectively. At the southeastern side of the peninsula, in Ghor Al Hadith, subsidence and sinkhole formation date back to the 1960’s, and are causing serious damage and threat to farmers.

SAR data for this study were collected by the European Space agency Remote Sensing Satellites ERS-1 and ERS-2. The SAR operates in C-band at a wavelength of 5.6 cm, and the orbital cycle for each satellite is 35 days. For this study we used 17 scenes from two SAR frames about 100 X 100 km each: frame 2979 (descending track, 12 scenes) and 0621 (ascending track, 5 scenes). Topographic phase was generated with a tandem pair of about 50-m baseline. Change interferograms were generated for different time intervals of 2 to 71 months between 1992 and 1999.

Change interferograms show a large diversity of uplift and subsidence features in the peninsula (Figure 2a): (i) The Lisan Peninsula is surrounded by an uplifting coast (Figure 2b). Complex interferograms of 22 months shows uplift of about 3cm over 600 m (1.5 cm/year). (ii) A few curvilinear shallow depressions are found above the presumed margins of the salt domes in the southern part of the peninsula (Figure 2c). The phase differences show localised subsidence of 4 cm in 28 months (1.7 cm/year).

The differential interferogram shows uplift features only in the northern part of the peninsula. Moreover the average uplift rate has been found (1.5 cm/year) in the peninsula is much higher than the geological average rate of 1-2 mm/year. The average subsidence rate is higher than the uplift rate and the polarisation along the peninsula suggests a special geophysical mechanism that has to be investigated. Comparing the displacements with the actual acquisition dates of the interferogrames, reveals that the highest subsidence rates are found in the 1995-1997 interferograms. This could infer that the settling followed a certain trigger November 22, 1995 Mw=7.1 Nuweiba Earthquake in the Gulf of Eilat, about 300 km south of the Dead Sea.

Plan for the year 2001

  • Studying the displacement mechanism of the Dead Sea salt diapirs using combined SAR interferometry and seismic data.
  • Finish analysing the hyperspectral DAIS-7915 data.
  • Airborne campaign of the hyperspectral sensor AISA over the Dead Sea. During the campaign a field survey is planed for mineral exploration.
  • Studying the benefit of using satellite hyperspectral data for geological research in the Dead Sea by analysing the ASTER data.

Completed Ph.D. courses

(1) tg104 Principles of remote sensing.

(2) tg215 Principles of GIS.

(3) tg 114 Field and Imaging Spectrometry for Geologists.

Publication

Shimoni, M., F. van der Meer, E. Ben-Dor; Detection of neotectonic features using hyperspectral and SAR data, Amazijahu fault, Dead sea rift, Israel., Second EARsel workshop on Imaging Spectroscopy, Enschede, 2000, The Netherlands.