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  • 1
    Language: English
    In: Sedimentology, 2015-02, Vol.62 (2), p.516-540
    Description: Quaternary reef development and demise have been shown to correspond to worldwide sea‐level fluctuations and related environmental changes, yet the mechanisms and rates affecting this relationship are not well resolved. A set of high‐resolution seismic reflection and multibeam bathymetric data were interpreted. Six distinct systems of relict fringing reefs embedded within the sedimentary cover of the northern shelf of the Gulf of Elat/Aqaba were identified. The two uppermost relict fringing reefs are also exposed on the sea floor in water depths of ca 20 m and ca 60 m, along the north‐western corner of the northern Gulf of Elat/Aqaba and sub‐parallel to the current northern coast, respectively. Two other relict fringing reefs are laterally correlated to each of the last two transgressive cycles, and are inferred to have formed during decelerations in sea‐level rise during the last two deglaciations. These reefs and the units to which they are laterally correlated portray a repeating stratigraphic pattern of reef development during deposition of seismically homogeneous sediment and an ensuing demise during deposition of heterogeneous sediment. Correlation of the reef stratigraphy with rates of Late Quaternary sea‐level rise and a sediment accumulation rate from one shelf core provide age estimations for the seismic stratigraphy. Two phases of fringing reef generation occurred during the last deglaciation (since ca 18 ka); the older reef probably developed between 12·8 ka and 11·5 ka at ca 60 m below present sea‐level and the younger reef after 8·4 to 8·0 ka at ca 20 m below present sea‐level. These last two phases of reef generation are separated by a lobate seismic unit that is interpreted as fluvial‐deltaic deposits that backstepped across the shelf during the Early Holocene transgression. Results suggest that fringing reefs evolved along the northern shelf of the Gulf of Elat/Aqaba only during relative decelerations in sea‐level rise, contemporaneous with low input of terrigenous sediment and probably during a period of aridity. At present, no fringing reef grows along the northern coast of the Gulf of Elat/Aqaba, suggesting that these relatively arid periods may have been drier than Recent. The pattern of slowdown in sea‐level rise contemporaneous with conditions of increased aridity seems to have repeated during the last two sea‐level rises, approximately at the same sea‐levels, suggesting a common mechanism of short (millennium‐scale) phases of eustatic and climatic alteration during deglaciations.
    Subject(s): Climate change ; Climatic changes ; fringing reef ; high-resolution ; Quaternary ; Reefs ; sea-level ; Sediments (Geology) ; seismic reflection ; seismic stratigraphy ; sequence stratigraphy
    ISSN: 0037-0746
    E-ISSN: 1365-3091
    Source: Hellenic Academic Libraries Link
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  • 2
    Language: English
    In: Geo-marine letters, 2010-02-24, Vol.30 (6), p.561-573
    Description: A high-resolution marine geophysical study was conducted during October-November 2006 in the northern Gulf of Aqaba/Eilat, providing the first multibeam imaging of the seafloor across the entire gulf head spanning both Israeli and Jordanian territorial waters. Analyses of the seafloor morphology show that the gulf head can be subdivided into the Eilat and Aqaba subbasins separated by the north-south-trending Ayla high. The Aqaba submarine basin appears starved of sediment supply, apparently causing erosion and a landward retreat of the shelf edge. Along the eastern border of this subbasin, the shelf is largely absent and its margin is influenced by the Aqaba Fault zone that forms a steep slope partially covered by sedimentary fan deltas from the adjacent ephemeral drainages. The Eilat subbasin, west of the Ayla high, receives a large amount of sediment derived from the extensive drainage basins of the Arava Valley (Wadi ’Arabah) and Yutim River to the north–northeast. These sediments and those entering from canyons on the south-western border of this subbasin are transported to the deep basin by turbidity currents and gravity slides, forming the Arava submarine fan. Large detached blocks and collapsed walls of submarine canyons and the western gulf margin indicate that mass wasting may be triggered by seismic activity. Seafloor lineaments defined by slope gradient analyses suggest that the Eilat Canyon and the boundaries of the Ayla high align along north- to northwest-striking fault systems—the Evrona Fault zone to the west and the Ayla Fault zone to the east. The shelf–slope break that lies along the 100 m isobath in the Eilat subbasin, and shallower (70–80 m isobaths) in the Aqaba subbasin, is offset by approx. 150 m along the eastern edge of the Ayla high. This offset might be the result of horizontal and vertical movements along what we call the Ayla Fault on the east side of the structure. Remnants of two marine terraces at 100 m and approx. 150 m water depths line the southwest margin of the gulf. These terraces are truncated by faulting along their northern end. Fossil coral reefs, which have a similar morphological appearance to the present-day, basin margin reefs, crop out along these deeper submarine terraces and along the shelf–slope break. One fossil reef is exposed on the shelf across the Ayla high at about 60–63 m water depth but is either covered or eroded in the adjacent subbasins. The offshore extension of the Evrona Fault offsets a fossil reef along the shelf and extends south of the canyon to linear fractures on the deep basin floor.
    Subject(s): Basins (Geology) ; Coral reefs and islands ; Earth and Environmental Science ; Earth Sciences ; Fractures ; Geology ; Geophysics ; Original ; Sediments (Geology) ; Submarine boats ; Submarine valleys ; Tectonics (Geology)
    ISSN: 0276-0460
    E-ISSN: 1432-1157
    Source: Springer Online Journal Archives (DFG Nationallizenzen)
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
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  • 3
    Language: English
    In: Journal of geophysical research. Solid earth, 2014-12, Vol.119 (12), p.9183-9205
    Description: The northern Gulf of Elat/Aqaba is located in the transition between the deep marine basins of the gulf and the shallow onland basins of the Arava Valley. Interpretation of 500 km of high‐resolution seismic reflection data collected across the northern shelf reveals the tectonic structure and evolution of this transition. Six NNE‐trending faults and one E‐W trending transverse fault are mapped. Slip rates are calculated based on measured offsets and age determination based on a radiocarbon‐calibrated sedimentation rate and a Quaternary age model. The most active fault is the Evrona Fault that absorbs most of the left lateral slip within the basin with an average sinistral slip rate of 0.7 ± 0.3 mm/yr through the Late Pleistocene and 2.3–3.4 mm/yr during the Holocene. Two intrabasin faults east of the Evrona Fault that have been inactive for the last several tens of thousands of years were mapped, and motion from these faults has likely transferred to the Evrona Fault. The basin is flanked on the west by the Elat Fault and on the east by the Aqaba Fault. Both faults are marked by large bathymetric escarpments. Based on displaced seismic reflectors, we calculate a Holocene vertical slip rate of 1.0 ± 0.2 and 0.4 ± 0.1 mm/yr for the Elat and Aqaba Faults, respectively. The geometry, slip rates, and slip history of the northern Gulf of Elat/Aqaba faults show that during the Late Pleistocene several intrabasin faults became dominant across the basin but that during the Holocene the Evrona Fault accommodates most of the strike slip. Key Points The study reveals six intrabasin north trending faults and one transverse faultThe Evrona strike‐slip fault occupies most of the Holocene left lateral slipThe northern GEA basin is in an advanced stage of evolution
    Subject(s): basin ; Basins ; Dead Sea ; Evolution ; fault ; Faults ; Gulf of Aqaba ; Gulfs ; Mathematical models ; Slip ; Strikes ; tectonic ; Tectonics ; Transform
    ISSN: 2169-9313
    E-ISSN: 2169-9356
    Source: Alma/SFX Local Collection
    Source: Wiley-Blackwell Full Collection 2014
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  • 4
    Language: English
    In: Journal of seismology, 2006-10-01, Vol.10 (4), p.415-430
    Description: Byline: Jeremy M. Haynes (1), Tina M. Niemi (1), Mohammad Atallah (2) Keywords: archaeoseismology; Dead Sea Transform fault system; earthquake; Jordan; paleoseismology; Wadi Araba; cistern The archaeological site of Qasr Tilah, in the Wadi Araba, Jordan is located on the northern Wadi Araba fault segment of the Dead Sea Transform. The site contains a Roman-period fort, a late Byzantine--Early Umayyad birkeh (water reservoir) and aqueduct, and agricultural fields. The birkeh and aqueduct are left-laterally offset by coseismic slip across the northern Wadi Araba fault. Using paleoseismic and archaeological evidence collected from a trench excavated across the fault zone, we identified evidence for four ground-rupturing earthquakes. Radiocarbon dating from key stratigraphic horizons and relative dating using potsherds constrains the dates of the four earthquakes from the sixth to the nineteenth centuries. Individual earthquakes were dated to the seventh, ninth and eleventh centuries. The fault strand that slipped during the most recent event (MRE) extends to just below the modern ground surface and juxtaposes alluvial-fan sediments that lack in datable material with the modern ground surface, thus preventing us from dating the MRE except to constrain the event to post-eleventh century. These data suggest that the historical earthquakes of 634 or 659/660, 873, 1068, and 1546 probably ruptured this fault segment. Author Affiliation: Article History: Registration Date: 01/08/2006 Received Date: 10/03/2005 Accepted Date: 02/06/2006 Online Date: 08/11/2006
    Subject(s): Archaeology ; Earthquakes ; Excavations (Archaeology)
    ISSN: 1383-4649
    E-ISSN: 1573-157X
    Source: Alma/SFX Local Collection
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  • 5
    Language: English
    In: Journal of seismology, 2001-07-01, Vol.5 (3), p.449-474
    Description: The Wadi Araba Valley is a morphotectonic depression along part of the Dead Sea Transform (DST) plate boundary that separates the Arabian plate on the east from the Sinai subplate on the west. The Wadi Araba fault (WAF) is one of the main strike-slip faults between the Gulf of Aqaba and the E-W trending Khunayzira (Amatzayahu) fault that bounds the southern end of the Dead Sea. Just south of the Dead Sea, the WAF cuts across several generations of alluvial fans that formed on tributaries to the Wadi Dahal after the regression of Late Pleistocene Lake Lisan ca. 15 ka. Geomorphic and stratigraphic evidence of active faulting, including left-laterally offset stream channels and alluvial-fan surfaces, yielded fault slip-rate data for the northern segment of WAF. Typical cumulative displacements of 54 m, 39 m, and 22.5 m of stream channels and alluvial-fan surfaces across the fault were measured from detailed geologic and topographic mapping. The 54 m offset of the oldest alluvial-fan surface (Q subscript f1) occurred after the final lowering of Lake Lisan (16-15 ka) and before 11 ka yielding a slip-rate range of 3.4 mm/yr to 4.9 mm/yr. Based on radiocarbon ages of charcoal and land snail shell samples from the buried Q subscript f2 alluvial-fan deposits exposed in trenches excavated across the fault, the 39 m and 22.5 m offsets occurred after 9 ka and 5.8 ka, respectively. These data yield a slip-rate range between 3.9 mm/yr and 6.0 mm/yr. The small variability in these slip-rate estimates for different time periods suggests that the northern Wadi Araba fault has maintained a relatively constant slip rate in the past 15 ka. An average slip rate of 4.7 plus/minus 1.3 mm/yr since 15 ka was calculated based on the three separate displacements and age estimates. Five separate offsets of 3 m were measured from gully bends and the offset of small fault-scarp alluvial fans. These displacement data suggest a coseismic slip of 3 m in the last earthquake, or a cumulative slip of 3 m in the past few earthquakes. A maximum slip of 3 m correspond to a Mw 7 earthquake that ruptures about 49 km of fault length. Using an average slip rate of 4.7 plus/minus 1.3 mm/yr together with a 3-m slip-per-event suggests a maximum earthquake recurrence interval of this fault segment of 500 to 885 years.
    ISSN: 1383-4649
    E-ISSN: 1573-157X
    Source: Springer Online Journal Archives (DFG Nationallizenzen)
    Source: Alma/SFX Local Collection
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  • 6
    Language: English
    In: Journal of coastal research, 1996-01-01, Vol.12 (1), p.90-102
    Description: Maps of the Tomales Bay and Olema Valley region, located 65 km north of San Francisco, were first published about 1860. We compared these maps with more recent topographic maps to determine geomorphological changes in the tidal marsh at the head of Tomales Bay and within the lower reach of Olema Creek, one of its tributaries. The accumulation of a significant volume of sediment in Tomales Bay is documented by shoreline progradation between 1862 and 1954, with the bulk occurring before 1918. This deposition probably reflects landscape instability caused by the introduction of livestock, agriculture, and non-native vegetation and by intensive logging within the watershed. The depositional history of Tomales Bay is undoubtedly similar to that of Bolinas Lagoon, another submerged part of the San Andreas fault zone closer to San Francisco. Map comparisons show that the downstream reach of Olema Creek actively meandered across its floodplain until the early 1920's. Stratigraphic evidence for a late Holocene channel of Olema Creek 300 m west of its present position was exposed in trenches near the town of Olema. This buried channel and its associated overbank deposits confirm that until recently the Olema Creek floodplain was a naturally aggrading environment. Presently, the channel of Olema Creek is entrenched several meters into its floodplain. This incision probably was triggered by artificially straightening the channel near its mouth, causing the gradient to increase.
    Subject(s): Creeks ; Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; Floodplains ; Geology ; Isotope geochemistry ; Isotope geochemistry. Geochronology ; Lagoons ; Maps ; Marine and continental quaternary ; Marshes ; Salt marshes ; Sediments ; Surficial geology ; Tributaries ; Valleys
    ISSN: 0749-0208
    E-ISSN: 1551-5036
    Source: JSTOR Life Sciences
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  • 7
    Language: English
    In: Marine geology, 2000, Vol.162 (2), p.237-258
    Description: A high-resolution seismic-reflection survey of the Transkei Basin and Natal Valley permits the first recognition of three major reflectors that mark basin-wide unconformities across the continental rise and deep abyssal plain off the southeast African continental margin. Reflector O marks a change in acoustic reflectivity, coincident with a change in sedimentary bedforms from generally parallel bedding below to large-scale lenticular and clinoform shapes above. Reflector O probably marks the onset of cold, abyssal current circulation around the Eocene–Oligocene boundary. The overlying O sequence records deposition of a contourite drift (Oribi Drift) by northeast flowing abyssal currents at ∼4000 m water depths along the continental rise of the northeastern Agulhas Fracture Zone. This water depth is shallower than present-day Antarctic Bottom Water (AABW). The M reflector unconformity (possibly lower Middle Miocene) marks seafloor erosion in 4500 m water depth in the Transkei Basin and the cessation of drift construction along the continental rise. Above reflector M in the abyssal plain, a contourite drift (M-Drift) records deposition from an east-flowing bottom current in a location similar to, but slightly shallower than present-day AABW. The stagnation of bottom current activity in the northern Natal Valley and/or a rapid influx of sediment accumulation is marked by M sequence turbidite sediments (the Mzimkulu apron) deposited against and burying the Oribi Drift on the continental rise. Reworking of M sequence sediment along the continental rise to form low mounds (M 4) and sediment waves in the northern Natal Valley indicate that a shallow, bottom current flowed at depths of 3800 to 3600 m. The coeval current-molding of the slope and abyssal plain indicates a two-layered structure of the bottom water may have commenced in the Miocene. Reflector P is the most pronounced unconformity in the deep abyssal plain, where it truncates M Sequence reflectors, and marks the base the Agulhas Drift which stands approximately 200 m above the surrounding seafloor. The P Sequence sedimentation is estimated to have begun in the Pliocene prior to or concurrent with an expansion of Southern and Northern polar ice-caps. Major slumping of the continental slope in the Natal Valley also began at this time, probably triggered by a combination of onland neotectonic activity and erosion of the base of the slope by vigorous bottom currents (possibly North Atlantic Deep Water, NADW).
    Subject(s): AABW ; contourites ; drift ; palaeoceanography ; southeast Africa continental margin
    ISSN: 0025-3227
    E-ISSN: 1872-6151
    Source: Backfile Package - All of Back Files EBS [ALLOFBCKF]
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  • 8
    Language: English
    In: Bulletin of the Seismological Society of America, 2014-06, Vol.104 (3), p.1299-1328
    Description: Stress changes produced by the 1906 San Francisco earthquake had a profound effect on the seismicity of the San Francisco Bay region (SFBR), dramatically reducing it in the twentieth century. Whether the SFBR is still within or has emerged from this seismic quiescence is an issue of debate with implications for earthquake mechanics and seismic hazards. Historically, the SFBR has not experienced one complete earthquake cycle (i.e., the accumulation of stress, its release primarily as coseismic slip during surface-faulting earthquakes, its re-accumulation in the interval following, and its subsequent rerelease). The historical record of earthquake occurrence in the SFBR appears to be complete at about M 5.5 back to 1850 (Bakun, 1999). For large events, the record may be complete back to 1776, which represents about half a cycle. Paleoseismic data provide a more complete view of the most recent pre-1906 SFBR earthquake cycle, extending it back to about 1600. Using these, we have developed estimates of magnitude and seismic moment for alternative sequences of surface-faulting paleoearthquakes occurring between 1600 and 1776 on the region"s major faults. From these we calculate seismic moment and moment release rates for different time intervals between 1600 and 2012. These show the variability in moment release and suggest that, in the SFBR regional plate boundary, stress can be released on a single fault in great earthquakes such as that in 1906 and in multiple ruptures distributed on the regional plate boundary fault system on a decadal time scale.
    Subject(s): California ; catalogs ; Cenozoic ; cycles ; earthquakes ; faults ; geologic hazards ; Holocene ; magnitude ; natural hazards ; paleoseismicity ; plate boundaries ; Quaternary ; risk assessment ; San Francisco Bay region ; seismic moment ; seismic quiescence ; seismic risk ; seismicity ; Seismology ; United States
    ISSN: 0037-1106
    E-ISSN: 1943-3573
    Source: Get It Now
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  • 9
    Language: English
    In: Journal of Geophysical Research, 1999-08-10, Vol.104 (B8), p.17617-17625
    Description: The northern basin of the Dead Sea is occupied by a ∼300‐m‐deep lake. A series of cores in the deep‐water part of the lake provide information about the top 365 cm of the sediments. The cores were correlated with high‐resolution 3.5‐kHz seismic profiles from this area and provide lithologic and age constraints for the high‐resolution seismic reflection data. Visual comparison of the two data sets shows that strong surface and shallow subsurface reflectors (A and B) correlate to the massive salt at the seafloor surface and the indurated salt at the base of the cores, respectively. Calculations of an average seismic velocity based on the interval between these reflectors and the corresponding sedimentary thickness yield an average 3500 m/s velocity. This agrees closely with velocities determined from direct measurements of compressional velocities for sediment samples. Ultrasonic wave velocity measurements of salt samples from the cores and dry rock salt cores from the southern basin of the Dead Sea indicate that wave velocities are independent of the burial depth at shallow depths; however, velocities show strong dependence on porosity. At low hydrostatic pressure a reduction in porosity as well as closure of microcracks in the crystals cause an increase in the velocities. This increase disappears at higher stress levels. Synthetic seismograms of the upper 3 ms and the entire 25 ms penetrated by the seismic profiles reinforce the lithologic and seismic stratigraphic correlation and confirm that prominent reflectors in the basin represent the top boundary of halite layers which are separated by laminated sequences of evaporites and elastics. The salt in the upper salt sequence is deposited at a very fast rate of more than 20 mm/yr. However, at shallow depths, considerable compaction takes place. Variations in appearance and velocities of the upper salt sequence and middle salt sequence indicate that the porous, granular, and fine‐grained precipitates of the surface salts are diagenetically altered to a coarse and compact crystalline aggregate by re‐solution and crystallization with burial. The sedimentary sequences recovered in the cores suggest that significant lake level fluctuations took place in the past in response to climatic changes. The detailed correlation of the cores and seismic profiles makes it possible to extrapolate climatic data from earlier periods beneath the maximum core penetration by analyzing the seismic stratigraphic sequences of the seismic reflection data.
    Subject(s): Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; Marine and continental quaternary ; Surficial geology
    ISSN: 0148-0227
    E-ISSN: 2156-2202
    Source: Wiley Online Library All Backfiles
    Source: Alma/SFX Local Collection
    Source: Wiley-Blackwell Full Collection 2014
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  • 10
    Language: English
    In: Geology (Boulder), 1994-05, Vol.22 (5), p.395-398
    Description: Seismic-reflection data and historical accounts suggest that a large submarine slump in the Dead Sea was produced by the most recent large earthquake along the Dead Sea-Jordan transform plate boundary, the ML 6.25 Jericho earthquake of July 11, 1927. The correlation supports the use of seismically triggered slump, landslide, and other sediment failures in lakes to infer the timing of paleoearthquakes. Furthermore, the location of the submarine slump adds to evidence that the 1927 earthquake was caused by rupture on a fault segment beneath the north basin of the Dead Sea. This fault rupture implies that the strain accumulation on the Jordan fault north of the Dead Sea is higher than previously recognized. Older seismically triggered slumps buried beneath the 1927 slump show that a record of ancient Jericho earthquakes can also be found in the sedimentary record. The estimated number and age range of these slumps suggest a long average earthquake recurrence time.
    Subject(s): active faults ; Analysis ; applied (geophysical surveys & methods) ; Asia ; Dead Sea ; deltas ; earthquake prediction ; earthquakes ; faults ; geologic hazards ; Geology, Structural ; geophysical methods ; geophysical profiles ; geophysical surveys ; Geophysics ; Jericho earthquake 1927 ; Jordan Fault ; Jordan River delta ; Lake sediments ; marine environment ; mass movements ; Middle East ; Morphotectonics ; paleoseismicity ; plate boundaries ; plate tectonics ; reflection methods ; rupture ; sedimentary structures ; seismic methods ; seismic profiles ; Seismological research ; Seismology ; slump structures ; slumping ; soft sediment deformation ; strain ; strike-slip faults ; submarine environment ; Submarine geology ; surveys ; transform faults
    ISSN: 0091-7613
    E-ISSN: 1943-2682
    Source: Get It Now
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