Eigenrays in 3D heterogeneous anisotropic media,Part I: Kinematics

We present a new ray bending approach, referred to as the Eigenray method, for solving two‐point boundary‐value kinematic and dynamic ray tracing problems in 3D smooth heterogeneous general anisotropic elastic media. The proposed Eigenray method is aimed to provide reliable stationary ray path solutions and their dynamic characteristics, in cases where conventional initial‐value ray shooting methods, followed by numerical convergence techniques, become challenging. The kinematic ray bending solution corresponds to the vanishing first traveltime variation, leading to a stationary path between two fixed endpoints (Fermat's principle), and is governed by the nonlinear second‐order Euler–Lagrange equation. The solution is based on a finite‐element approach, applying the weak formulation that reduces the Euler–Lagrange second‐order ordinary differential equation to the first‐order weighted‐residual nonlinear algebraic equation set. For the kinematic finite‐element problem, the degrees of freedom are discretized nodal locations and directions along the ray trajectory, where the values between the nodes are accurately and naturally defined with the Hermite polynomial interpolation. The target function to be minimized includes two essential penalty (constraint) terms, related to the distribution of the nodes along the path and to the normalization of the ray direction. We distinguish between two target functions triggered by the two possible types of stationary rays: a minimum traveltime and a saddle‐point solution (due to caustics). The minimization process involves the computation of the global (all‐node) traveltime gradient vector and the traveltime Hessian matrix. The traveltime Hessian is used for the minimization process, analysing the type of the stationary ray, and for computing the geometric spreading of the entire resolved stationary ray path. The latter, however, is not a replacement for the dynamic ray tracing solution, since it does not deliver the geometric spreading for intermediate points along the ray, nor the analysis of caustics. Finally, we demonstrate the efficiency and accuracy of the proposed method along three canonical examples.     

Active faulting in the dead sea rift

Manifestations of Late Quaternary and Holocene faulting were studied in a 500 km long segment of the Dead Sea transform (rift). Most prominent are left-slip faults, whose characteristic physiographic features are recognizable along most of the studied segment. Where these faults bend or are stepped to the left, rhomb-shaped grabens (or pull aparts) are produced, forming depressions. In the reverse situation compressional features such as pressure ridges, domes and folds form positive topographic features. Such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers. Normal faults, sub-parallel to the left slip faults, produce a trough-like valley along much of the Dead Sea transform, but are most prominent along the margins of the large rhomb-grabens, e.g., the Dead Sea trough. They apparently record a small component of transverse extension. Generally, their motion is slow: young slip did not occur along some segments during the last few 10⁴ y. Elsewhere throws of 10–20 m at least occurred in this period. The Dead Sea transform is seismically active. The instrumental and historic records indicate a seismic slip rate of 0.15–0.35 cm/y during the last 1000–1500 y, while estimates of the average Pliocene—Pleistocene rate are 0.7–1.0 cm/y. Either much creep takes place, or the slip rate varies over periods of a few 10³ y.     

Tectonic evolution of the Qumran Basin from high-resolution 3.5-kHz seismic profiles and its implication for the evolution of the northern Dead Sea Basin

The Dead Sea Basin is a morphotectonic depression along the Dead Sea Transform. Its structure can be described as a deep rhomb-graben (pull-apart) flanked by two block-faulted marginal zones. We have studied the recent tectonic structure of the northwestern margin of the Dead Sea Basin in the area where the northern strike-slip master fault enters the basin and approaches the western marginal zone (Western Boundary Fault). For this purpose, we have analyzed 3.5-kHz seismic reflection profiles obtained from the northwestern corner of the Dead Sea. The seismic profiles give insight into the recent tectonic deformation of the northwestern margin of the Dead Sea Basin. A series of 11 seismic profiles are presented and described. Although several deformation features can be explained in terms of gravity tectonics, it is suggested that the occurrence of strike-slip in this part of the Dead Sea Basin is most likely. Seismic sections reveal a narrow zone of intensely deformed strata. This zone gradually merges into a zone marked by a newly discovered tectonic depression, the Qumran Basin. It is speculated that both structural zones originate from strike-slip along right-bending faults that splay-off from the Jordan Fault, the strike-slip master fault that delimits the active Dead Sea rhomb-graben on the west. Fault interaction between the strike-slip master fault and the normal faults bounding the transform valley seems the most plausible explanation for the origin of the right-bending splays. We suggest that the observed southward widening of the Dead Sea Basin possibly results from the successive formation of secondary right-bending splays to the north, as the active depocenter of the Dead Sea Basin migrates northward with time.     

Hydrous pyrolysis of Monterey asphaltenes

Hydrous pyrolysis of asphaltenes has been tested as a method to reconstruct the chemical composition of biodegraded oils and oil seeps. The asphaltenes of three oils (a nondegraded oil, a biodegraded oil, and a biodegraded oil seep) from the Monterey Formation were studied. Results show that the aliphatic fraction generated by hydrous pyrolysis is very similar in chemical composition to the non-degraded oil. This makes the method very useful in correlation studies of biodegraded and nondegraded oils. It also allows to roughly estimate the maturity of the source of the biodegraded oil or oil seep.     

The origin of the Dead Sea rift

The Dead Sea rift is considered to be a plate boundary of the transform type. Several key questions regarding its structure and evolution are: Does sea floor spreading activity propagate from the Red Sea into the Dead Sea rift? Did rifting activity start simultaneously along the entire length of the Dead Sea rift, or did it propagate from several centres? Why did the initial propagation of the Red Sea into the Gulf of Suez stop and an opening of the Gulf of Elat start?

Using crustal structure data from north Africa and the eastern Mediterranean and approximating the deformation of the lithosphere by a deformation of a multilayer thin sheet that overlies an inviscid half-space, the regional stress field in this region was calculated. Using this approach it is possible to take into account variations of lithospheric thickness and the transition from a continental to an oceanic crust. By application of a strain-dependent visco-elastic model of a solid with damage it is possible to describe the process of creation and evolution of narrow zones of strain rate localization, corresponding to the high value of the damage parameter i.e. fault zones.

Mathematical simulation of the plate motion and faulting process suggests that the Dead Sea rift was created as a result of a simultaneous propagation of two different transforms. One propagated from the Red Sea through the Gulf of Elat to the north. The other transform started at the collision zone in Turkey and propagated to the south.     

Formation of sequential basins along a strike–slip fault–Geophysical observations from the Dead Sea basin

The Dead Sea basin is often cited as one of the classic examples for the evolution of pull-apart basins along strike–slip faults. Despite its significance, the internal structure of the northern Dead Sea basin has never been addressed conclusively. In order to produce the first comprehensive, high-resolution analysis of this area, all available seismic data from the northern Dead Sea (lake)–lower Jordan valley (land) were combined. Results show that the northern Dead Sea basin is comprised of a system of tectonically controlled sub-basins delimited by the converging Western and Eastern boundary faults of the Dead Sea fault valley. These sub-basins grow shallower and smaller to the north and are separated by structural saddles marking the location of active transverse faults. The sedimentary fill within the sub-basins was found to be relatively thicker than previously interpreted. As a result of the findings of this study, the “classic” model for the development of pull-aparts, based on the Dead Sea, is revised. The new comprehensive compilation of data produced here for the first time was used to improve upon existing conceptual models and may advance the understanding of similar basinal systems elsewhere.     

Parameterization of a Composite Attenuation Relation for the Dead Sea Area Based on 3-D Modeling of Elastic Wave Propagation

3-D simulations of elastic wave propagation generated by earthquakes with magnitudes between 5.5 and 7.0 are used to parameterize strong ground motion attenuation relations for the Dead Sea Rift (DSR) graben structure. The results show that standard attenuation relations with an isotropic distance parameter are inadequate for a graben structure with a deep sedimentary trough. A new strategy is devised for the parameterization of attenuation relations in graben structures by looking at the statistical properties of 53 simulated earthquakes of variable magnitudes located at various sites along the western boundary fault of the DSR graben. An exemplary attenuation relation is designed from the synthetics for the 1 Hz spectral acceleration, modifying the Joyner-Boore-type parametrization by adding coefficients suited for three different source-to-sensor configurations: within the graben, beyond the graben and path unaffected by the graben structure.     

Assessment of transmission losses and groundwater recharge from runoff events in a wadi under shortage of data on lateral inflow,Negev, Israel

A hydrological–lithostratigraphical model was developed for assessment of transmission losses and groundwater recharge from runoff events in arid water courses where hydrological and meteorological records are incomplete. Water balance equations were established for reaches between hydrometric stations. Because rainfall and tributary flow data are scarce, lateral inflow, which is an essential component of the water balance equation, could not be estimated directly. The solution was obtained by developing a method which includes a hydrological–lithostratigraphical analogy. This is based on the following assumptions: (a) runoff resulting from a given rainfall event is related to the watershed surface lithology; (b) for a given event, the spatial distribution of runoff reflects the distribution of rainfall: and (c) transmission losses are uniquely related to the total inflow to the reach. The latter relationship, called the loss function, and the water balance equation comprise a model which simultaneously assesses lateral inflow and transmission losses for runoff events recorded at the terminal stations. The model was applied to three reaches of the arid Nahal Tsin in Israel. In this case study, the transmission losses were of the same order of magnitude as the flow at the major hydrometric stations. The losses were subdivided into channel moistening, which subsequently evaporates, and deep percolation, which recharges groundwater. For large runoff events, evaporation was substantially smaller than the losses. The mean annual recharge of groundwater from runoff events in the Tsin watershed was 4·1×10⁶ m³, while the mean annual flow volume at the major stations ranged from 0·6 to 1·5×10⁶ m³. Once in 100 years, the annual recharge may be seven times higher than the mean annual value, but the recharge during most years is very small. Copyright © 1999 John Wiley & Sons, Ltd.     

Between plate and salt tectonics—New stratigraphic constraints on the architecture and timing of the Dead Sea basin during the Late Quaternary

The Dead Sea is an extensional basin developing along a transform fault plate boundary. It is also a terminal salt basin. Without knowledge of precise stratigraphy, it is difficult to differentiate between the role of plate and salt tectonics on sedimentary accumulation and deformation patterns. While the environmental conditions responsible for sediment supply are reasonably constrained by previous studies on the lake margins, the current study focuses on deciphering the detailed stratigraphy across the entire northern Dead Sea basin as well as syn and post-depositional processes. The sedimentary architecture of the late Quaternary lacustrine succession was examined by integrating 851 km of seismic reflection data from three surveys with gamma ray and velocity logs and the stratigraphic division from an ICDP borehole cored in 2010. This allowed seismic interpretation to be anchored in time across the entire basin. Key surfaces were mapped based on borehole lithology and a newly constructed synthetic seismogram. Average interval velocities were used to calculate isopach maps and spatial and temporal sedimentation rates. Results show that the Amora Formation was deposited in a pre-existing graben bounded by two N-S trending longitudinal faults. Both faults remained active during deposition of the late Pleistocene Samra and Lisan Formations—the eastern fault continued to bound the basin while the western fault remained blind. On-going plate motion introduced a third longitudinal fault, increasing accommodation space westwards from the onset of deposition of the Samra Formation. During accumulation of these two formations, sedimentation rates were uniform over the lake and similar. High lake levels caused an increase in hydrostatic pressure. This led to salt withdrawal, which flowed to the south and southwest causing increased uplift of the Lisan and En Gedi diapirs and the formation of localized salt rim synclines. This induced local seismicity and slumping, resulting in an increased thickness of the Lisan succession within the lake relative to its margins. Sedimentation rates of the Holocene Ze'elim Fm were 4–5 times higher than before. The analysis presented here resolves central questions of spatial extent and timing of lithology, deposition rates and their variability across the basin, timing of faulting at and below the lake floor, and timing and extent of salt and plate tectonic phases and their effect on syn and post-depositional processes. Plate tectonics dictated the structure of the basin, while salt tectonics and sediment accumulation were primarily responsible for its fill architecture during the timeframe examined here.