Beverly Goodman Tchernov, Timor Katz, Yonathan Shaked, Nairooz Qupty, Mor Kanari, Tina Niemi, and Amotz Agnon. 2016. “Offshore evidence for an undocumented tsunami event in the 'low risk' Gulf of Aqaba-Eilat, northern Red Sea.” PLoS ONE.Abstract
Although the Gulf of Aqaba-Eilat is located in the tectonically active northern Red Sea, it has been described as low-risk with regard to tsunami activity because there are no modern records of damaging tsunami events and only one tsunami (1068 AD) referred to in historical records. However, this assessment may be poorly informed given that the area was formed by and is located along the seismically active Dead Sea Fault, its population is known to fluctuate in size and literacy in part due to its harsh hyper-arid climate, and there is a dearth of field studies addressing the presence or absence of tsunamigenic deposits. Here we show evidence from two offshore cores for a major paleotsunami that occurred \~2300 years ago with a sedimentological footprint that far exceeds the scarce markers of the historically mentioned 1068 AD event. The interpretation is based on the presence of a laterally continuous and synchronous, anomalous sedimentological deposit that includes allochtonous inclusions and unique structural characteristics. Based on sedimentological parameters, these deposits could not be accounted for by other transport events, or other known background sedimentological processes.
Dafna Langgut, Eli Yannai, Itamar Taxel, Amotz Agnon, and Shmuel Marco. 2016. “Resolving a historical earthquake date at Tel Yavneh (central Israel) using pollen seasonality.” Palynology.Abstract
The identification of historical events by geological and archaeological evidence is often ambiguous and conflicting, undermining the enormous potential for sub-annual precision in dating. The ruin of one of the largest pottery factories in the Middle East during Byzantine times, recently excavated in Yavneh (central Israel), exemplifies this: aligned fallen walls and columns and a kiln that collapsed while still in operation, with dozens of ceramic storage jars in articulation. Archaeological dating, which limits the time of the collapse to the seventh century CE, cannot distinguish between two large documented earthquakes that occurred during this century. By using pollen grains trapped by the collapse, we were able to distinguish, for the first time, between the two candidate earthquakes: September 634 CE and early June 659 CE. The pollen was extracted from the dust captured on the floor of the kiln during the cooling process of the vessels. The dust was collected only from below in situ whole vessels, and based on our reconstruction had been accumulated for about several days (after the heating process ended and before the collapse). Since the palynological assemblages included spring-blooming plants (such as Olea europaea and Sarcopoterium spinosum) and no common regional autumn bloomers (e.g. Artemisia), it is proposed that the kiln went out of use due to the early June 659 CE earthquake. We also propose that the recovery of the Yavneh workshops was no longer economically worthwhile, maybe in part due to changes in economic and political conditions in the region following the Muslim conquest.
Frédéric Masson, Yariv Hamiel, Amotz Agnon, Yann Klinger, and Aline Deprez. 2015. “Variable behavior of the Dead Sea Fault along the southern Arava segment from GPS measurements.” Comptes Rendus - Geoscience, 4, 347: 161–169.Abstract
The Dead Sea Fault is a major strike-slip fault bounding the Arabia plate and the Sinai subplate. On the basis of three GPS campaign measurements, 12. years apart, at 19 sites distributed in Israel and Jordan, complemented by Israeli permanent stations, we compute the present-day deformation across the Wadi Arava fault, the southern segment of the Dead Sea Fault. Elastic locked-fault modelling of fault-parallel velocities provides a slip rate of 4.7 ± 0.7. mm/yr and a locking depth of 11.6 ± 5.3 km in its central part. Along its northern part, south of the Dead Sea, the simple model proposed for the central profile does not fit the velocity field well. To fit the data, two faults have to be taken into account, on both sides of the sedimentary basin of the Dead Sea, each fault accommodating. 2 mm/yr. Locking depths are small (less than 2 km on the western branch, 6 km on the eastern branch). Along the southern profile, we are once again unable to fit the data using the simple model, similar to the central profile. It is very difficult to propose a velocity greater than 4 mm/yr, i.e. smaller than that along the central profile. This leads us to propose that a part of the relative movement from Sinai to Arabia is accommodated along faults located west of our profiles.
Ron Shaar, Hagai Ron, Lisa Tauxe, Ronit Kessel, Amotz Agnon, Erez Ben-Yosef, and Joshua M. Feinberg. 2010. “Testing the accuracy of absolute intensity estimates of the ancient geomagnetic field using copper slag material.” Earth and Planetary Science Letters.Abstract
The Middle-Eastern copper slag is a promising new material for studying intensity variations in the geomagnetic field with high resolution and precision. The purpose of this study is to test the accuracy of archaeointensity estimates determined using copper slag by addressing two questions: 1) "Does slag material display the magnetic properties required for valid Thellier experiments?" and 2) "What is the accuracy of the archaeointensity estimates derived from Thellier-style experiments on optimal samples?" We address the first question through a comprehensive microscopic and magnetic study of representative archaeological slag samples in order to identify the properties responsible for optimal behavior in Thellier experiments. To address the second question, we reproduced slag samples in the laboratory under controlled magnetic fields and analyzed them using the same IZZI paleointensity technique used for the ancient slag. Microscopic analyses of the archaeological slag show that ferromagnetic phases occur as three-dimensional dendritic structures whose branches consist of submicron-elongated particles. Magnetic analyses show that these dendrites behave as an assemblage of shape-controlled, single-domain-like particles and that their magnetization is thermoremanent. We conclude that slag material can be magnetically suitable for valid Thellier experiments. The laboratory-produced slag material demonstrated similar magnetic and mineralogical properties as the archaeological slag. IZZI experiments showed that non-linear TRM acquisition, even at field strengths similar to Earth's, and TRM anisotropy are important factors to monitor during paleointensity studies of slag material. Anisotropy and non-linearity are probably related to the dendritic shape of the oxide grains. Intensity estimates derived from three laboratory-produced slag samples demonstrated accuracy to within ∼ 5% after applying the required corrections. © 2009 Elsevier B.V. All rights reserved.
Yizhaq Makovsky, Assaf Wunch, Ronen Ariely, Yonathan Shaked, Assaf Rivlin, Aldo Shemesh, Zvi Ben Avraham, and Amotz Agnon. 2008. “Quaternary transform kinematics constrained by sequence stratigraphy and submerged coastline features: The Gulf of Aqaba.” Earth and Planetary Science Letters.Abstract
The Dead Sea Fault System (DSFS) steps-over at the northern head of the Gulf of Aqaba (GOA), crossing the evolving continental shelf. We report detailed processing and interpretation of high resolution sub-bottom profiles of the north western tip of the GOA down to a depth of about 120??m. Our data reveal stepping seafloor morphology comprising a series of relict coastline features, primarily fossil reefs whose present depth results from the combined effect of sea level rise and tectonic displacements. On the northern slope, the fossil reefs are embedded in a predominantly single phase ??? 30??m thick retrograde sedimentary stack that evolved presumably during sea level rise since the last glacial maximum, about 20??Ka. Large variations in character within this sedimentary stack bear evidence for large episodic changes in the rates of sea level rise and ensuing environmental conditions during the Holocene. A prominent terrace and face, a suggested relict coastline feature, accommodated on the order of 10??m down to the east vertical offsets across the surveyed area at the north western GOA since submergence, presumably late Pleistocene to early Holocene. The trace of an active strike strike-slip fault crossing the northern slope is defined by: a. NE striking bathymetric features; b. discontinuities offsetting the sedimentary layering from just below the sea floor to the deepest layers imaged; c. a 30 ?? 10??m sinistral and 10 ?? 1??m down to the west offset of a fossil reef at a depth of about 65??m. Global sea level curves constrain the age of the 65-m deep reef to 11.5 ?? 2??Ka, yielding an estimated average Holocene sinistral slip rate of 2.7 ?? 1.5??mm/yr, about half the regional slip of the DSFS. We conclude that the submarine fault defined here is a principal strand of the DSFS, a southward left stepping echelon of the Avrona fault. Such secondary echelon segmentation may be typical for the accommodation of strike-slip at tips of transform basins. ?? 2008 Elsevier B.V. All rights reserved.
Alon Ziv, Allan M. Rubin, and Amotz Agnon. 2000. “Stability of dike intrusion along preexisting fractures.” Journal of Geophysical Research: Solid Earth.Abstract
We investigate the ability of magma to propagate along preexisting fractures oblique to the least compressive stress. Relaxation of the preexisting shear stress to zero over the portion of the fracture dilated by magma (the dike) results in slip for some distance along the closed portion of the fracture ahead of the dike tip and a stress concentration near the dike tip. This could lead to the production of new tensile cracks, oblique to the parent dike, that could capture the flow. If the sheer stress resolved on the fracture plane is perpendicular to the fracture front (mode I-II), the front may deviate along its entire length; if the shear stress is parallel to the fracture front (mode I-III) the front may splay into segments. For mode I-II dikes the maximum tensile stress occurs at the dike tip and is parallel to the dike. If the effective tensile stress exceeds the rock tensile strength, then the intruding magma, rather than dilating the existing fracture, is expected to propagate into a self-generated crack analogous to the ''wing cracks'' observed to form at the tips of pure mode II fractures. For mode I-III dikes the maximum tensile stress lies within the plane of the dike and is oriented at some angle that depends upon the far-field boundary conditions. Even if the magma pressure exceeds the ambient normal stress, it appears to be very difficult for dikes to intrude into preexisting fractures unless one or more of the following conditions is satisfied: (1) the fracture is nearly perpendicular to the least compressive stress; (2) the resolved shear stress on the fracture is small compared to the excess magma pressure (i.e., the ratio of shear to opening of the dike walls is small); (3) the effective ambient dike-normal stress is small compared to the rock tensile strength. This indicates that it may be quite difficult for dikes emerging from midcrustal to lower crustal depths to follow faults.