Sam Frydman

The lowest place on Earth is subsiding—An InSAR (interferometric synthetic aperture radar) perspective

Since the early 1990s, sinkholes and wide, shallow subsidence features (WSSFs) have become major problems along the Dead Sea shores in Israel and Jordan. Sinkholes are readily observed in the field, but their locations and timing are unpredictable. WSSFs are often difficult to observe in the field. However, once identified, they delineate zones of instability and increasing hazard. In this study we identify, characterize, and measure rates of subsidence along the Dead Sea shores by the interferometric synthetic aperture radar (InSAR) technique. We analyze 16 SAR scenes acquired during the years 1992 to 1999 by the European Remote Sensing ERS-1 and ERS- 2 satellites. The interferograms span periods of between 2 and 71 months. WSSFs are observed in the Lisan Peninsula and along the Dead Sea shores, in a variety of appearances, including circular and elongate coastal depressions (a few hundred meters to a few kilometers in length), depressions in ancient alluvial fans, and depressions along salt-diapir margins. Phase differences measured in our interferograms correspond to subsidence rates generally in the range of 0–20 mm/yr within the studied period, with exceptional high rates that exceed 60 mm/yr in two specific regions. During the study period, the level of the Dead Sea and of the associated ground water has dropped by ∼6 m. This water-level drop within an aquifer overlying fine-grained, marly layers, would be expected to have caused aquifer-system consolidation, resulting in gradual subsidence. Comparison of our InSAR observations with calculations of the expected consolidation shows that in areas where marl layers are known to compose part of the upper 30 m of the profile, estimated consolidation settlements are of the order of the measured subsidence. Our observations also show that in certain locations, subsidence appears to be structurally controlled by faults, seaward landslides, and salt domes. Gradual subsidence is unlikely to be directly related to the sinkholes, excluding the use of the WSSFs features as predictable precursors to sinkhole formation.

Site response analysis using a non-linear hysteretic model

A non-linear model for the description of soil response to earthquake loading is presented, and applied to the prediction of surface vibration for a given soil profile. The model is developed on the basis of well-established experimental trends with regard to the strain dependence of shear modulus and damping ratio, as well as cyclic degradation of stiffness. A constitutive equation for one-dimensional shear deformation is constructed on the basis of a hysteretic, frequency-independent damping model, with the assumption that elastic and damping coefficients are functions of mean values of deformation. One-dimensional propagation analyses are carried out by using the proposed model and an equivalent linear model, and the results are compared. The comparison highlights some limitations of the equivalent linear approach, and it is shown that these are solved by the new procedure.

Analysis of seismically triggered slides off Israel

Evidence of large submarine slides, presumably seismically triggered, is evident on the Israeli continental slope. This article presents a study of the earthquake characteristics which were likely to have caused these slides. Four seismic records with different characteristics were used as input, and propagation and response analyses were carried out. The results of these analyses suggest that the slides were caused by one or more large magnitude events resulting in low frequency tremors propagating through the slope profile. It is likely that these earthquakes were located on the Jordan Rift.

Non-aqueous-phase-liquid breakthrough during evaporative drying of clay barriers

In this study, an attempt has been made to model a real field scenario, whereby an initially almost saturated clay liner in a waste site is gradually drying, due to evaporation at its lower boundary. A detailed conceptual model that deals with the penetration and breakthrough of non-aqueous-phase-liquid (NAPL) in clay liners is introduced. Water content of clay samples was monitored during ambient evaporation through apertures at the base of sample holders. Clay drying rate served as the primary parameter for the NAPL breakthrough study. The interconnection between drying rates, structural damage formation (cracks and suction) and NAPL penetration is especially addressed. The processes taking place in the clay samples during drying appear to be associated with the capillary effects between the different fluid phases in the vicinity of either the NAPL-clay or the clay-air boundaries. A conceptual model of NAPL penetration and breakthrough of the clay layer has been considered, based on both indirect and direct observations of structural damages produced on either clay boundaries. A mutual interaction between these two boundaries is suggested and discussed. NAPL breakthrough is suggested to take place through cracks initiated on the upper soil surface.

Shear Strength and Negative Water Potential in Unsaturated, Compacted Clays

All measurements of suction in soil water actually measure water energy (potential) rather than the state of pressure (tension) in the soil water. Matrix potential in unsaturated clays includes capillary and adsorption components. While the capillary component may contribute to the pore stresses, adsorption potential (or adsorption suction), which is due to interaction between the clay particles and the soil water, cannot be considered a stress. The present paper discusses the relevance of this to the shear strength of unsaturated clays. For example, in view of its energetic rather than stress nature, adsorption suction cannot contribute to the frictional component of shear strength, but only to the cohesional component. Published data is used to examine the influence of suction on mechanical behavior of compacted clays, and a relationship is observed between suction, cohesion and the activity of the clay particles.