detection of neotectonic features combining advanced remote

Shimoni Michal (Ph.D. student)
Faculty of Civil Engineering and Geosciences
Department of Applied Earth Sciences
Section Earth Sciences
The objective of this research is that combining optical data, physical features extracted from radar data,
geophysical and environmental information can improve the understanding of tectonic processes in rift
areas. By using new analysis technique and environmental models the research will extract quantitative
information about surface mineralogy and biology from the optical data. The combination of data from
optical (DAIS-7915, AISA, ASTER) and microwave (ERS-1/2 and RADARSAT) remote sensing
instruments will be used to produce a model detecting minor faults caused by neotectonic processes in the
Dead Sea Rift, southern basin, Israel.
The Dead Sea depression comprises two basins, each approximately 50-60 km long, 15-17 km wide and
filled with up to 10 km of Neogene to recent sediments. Like basins in other large trans-current fault
systems, the DSB basins are considered to be pull-apart basins formed by offset along the strike-slip
faults. The two basins of the Dead Sea are separated by a structurally complex region, part of which is
occupied by the Lisan Peninsula, a salt diapir buried 100 m below the surface. Its original evaporites were
formed during the Pleistocene (Lisan formation) and overlaid by Holocene sediments (Ze’elim
Five differential interferograms were generated with time intervals of seven to ninety three months
between 1992 and 1999 (see Figure 1). Using the interferograms a deformation signal is observed at
different parts of the peninsula with subsidence rates of 1.0 to 15.0 mm/year and uplift rates of 0.2 to 1.5
mm/year. Uplift calculated for the Lisan diapir using classical geological rate is 1-2 mm/year (uplift rate
that is in correspondence with the inetrferometry measurement).
What is the mechanism that causes a deformation in the Lisan Peninsula salt wall? We investigated two
possibilities, salt tectonics and buoyancy forces.
Figure 1: Interferometry SAR data of the Lisan peninsula – 1: Amplitude image of ERS-1/2 tandem pairs 03439_23112
[16-17/12/95]; 2-5: Three-pass differential interferograms showing the location of: the cape (A); the intermediate zone
between the central dome and the cape (B); the central dome (C); the south dome (D) and Mor swamp (E). Every color
cycle relative to the reference area corresponds to 30 mm of vertical deformation. White arrows represent subsidence
areas, whereas black arrows indicate uplift areas.
A. Salt tectonics
Ten-Brink and Ben-Avraham (1989) proved with seismic profiles that diapir deformation at Mt. Sedom is
driven by Amaziahu fault, a listrict fault which is located south to the salt diapir. Little is known about the
eastern margin of the DSB and whether its structure is similar to the western margin. There is a possibility
that Boqeq fault, another listrict fault located south to the Lisan Peninsula, could be the initiating
mechanism of the diapirism deformation detected by interferometry. However, the location of Boqeq fault
was based only on analysis of a single line (seismic line 633, Ben-Avraham et al., 1990). Based on
additional subparallel seismic profiles (seismic line 1 and DS-7) investigated in this research, we believe
that this deformation represents the edge of a salt diapir, rather than a fault in the basin fill. In particular,
seismic line DS-7 running in the N-S direction rather East should cross the proposed Boqeq-fault, but
shows no evidence for an E-W crossing fault. The boundary between the zones of coherent reflectors and
chaotic reflectors in this profile is steep and overhanging, which is typical to the edges of many salt
diapirs. The clearest boundary (North of the salt massif) is located north of the proposed location of Boqeq
fault on line 633, and not south as predicted by a diagonal fault. Line 1 which runs parallel to line 633
about 1 km to the east shows the deformation of the overlying sediment more clearly than line 633. The
patches of coherent reflectors north of the previously assumed location of Boqeq fault in lines 1 and 633
were interpreted by Al-Zoubi and ten Brink (2001) to be regions where the seismic profile grazed in and
out of the undulating edge of the diapir. Therefore, we cannot determine from the seismic reflection lines
whether diagonal faults are present below the base of the basin fill.
B. Buoyancy forces
Salt domes are formed because salt is less dense than the overlying rock, and the salt “flows” upward due
to buoyancy. As the salt diapir begins to form a bulb in the parent sediment layers, it will deform the
overlying beds into a dome shape directly above the rising salt mass. In addition, salt from around the bulb
swell will migrate inwards towards the rising mass. Because of the displacement of this salt, the
overburden will subside around the bulb in the salt to form a rim syncline. If the salt mass continues to
rise, it may pierce the overlying rock layers, and salt from the mother layer will continue to flow laterally
to feed the rising diapir. Such diapirism occurs only under certain conditions. First, the rising material
must be less dense than the overlying sediment, or the source layer must be differentially loaded. Second,
there must be overburden pressure to initiate buoyant rising of the salt mass. Third, the diapir material
must have an `escape' route through the overburden. In order to initiate buoyant rising of the salt mass,
there must be a differential lateral pressure so that the rising potential of the salt is concentrated into one
Bartov (1999) found in his work that the thickness of the late sediments layer over the salt mass in the
Lisan peninsula is not enough to create a density inversion. However, a closer look at the topography and
the stratigraphy around the Lisan diapir shows a more complex diapiric growth than described above.
Onlap surfaces indicate two deformation phases along the western edge of the Lisan diapir and hinting
that the diapir continues to rise. Shortening of the roof and flanks of the diapir may indicate two pulses of
activity, possibly due to orthogonal compression. The earlier pulse occurred when the diapir was at or near
the surface. The upper onlap surface records indicate the start of a second period of activity, which
continues today.
Plan for the year 2003
 Using geophysical and polarymetric models to extract morphological data.
 Combine hyperspectral and microwave data to build relative geological age, mineralogical and
neotectonic maps of the DSB.