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The Dahuiyeh (Zarand) earthquake of 2005 February 22 in central Iran: reactivitation of an intra-mountain thrust
No full textWe used seismic body waves, radar interferometry and field investigation to examine the source processes of the destructive earthquake of 2005 February 22 near Zarand, in south–central Iran. The earthquake ruptured an intramountain reverse fault, striking E–W and dipping north at ∼60° to a depth of about 10 km. It produced a series of coseismic scarps with up to 1 m vertical displacement over a total distance of ∼13 km, continuous for 7 km. The line of the coseismic ruptures followed a known geological fault of unknown, but probably pre-Late Cenozoic, age and involved bedding-plane slip where the scarps were continuous at the surface. However, any signs of earlier coseismic ruptures along this fault had been obliterated by the time of the 2005 earthquake, probably by land sliding and weathering, so that the fault could not reasonably have been identified as active beforehand. The 2005 fault is at an oblique angle to the range-bounding Kuh Banan strike-slip fault, and may represent a splay from that fault, related to its southern termination. Other intramountain reverse faulting earthquakes have occurred in Iran, but this is the first to have produced a clear, mapped surface rupture, and to have been studied with InSAR. Faults of this type represent a serious seismic hazard in Iran and are difficult to assess, because their geomorphological expression is much less clear than the range-bounding reverse faults, which are more common and have been better studied
Experimental channel response to tectonic uplift
No full textWe have performed a series of experiments to investigate the relationship between channel geometry and tectonic forcing in steady state landscapes at various uplift rates. The experimental setup consists of uniformly uplifted silica paste eroded by artificial rainfall. In this setup, erosional landscapes evolve by growth and amalgamation of incisions, which organize into a drainage network whose dynamics are a function of the interaction between vertical channel cutting, hillslope erosion, and sediment transport. High-precision (0.5 mm pixel size) digital elevation models were constructed using a stereogrammetric camera system. From this data, channel bed slope was found to be independent of discharge and position on the experimental surface and to increase linearly with uplift rate. Geometric parameters of the flow, such as channel width or depth, could not be observed directly during the experiments. Using laminar flow equations for the mean flow velocity, these parameters were back calculated, and relationships to the imposed substrate uplift rate were derived. Channel width, cross-sectional area, and wetted perimeter decrease with increasing uplift rate to a limit value, hydraulic radius and flow depth increase slightly, and flow velocity increases approximately linearly with increasing uplift rate. These results are qualitatively consistent with recent field surveys and highlight the importance of channel width and slope variations in accommodating channel response to variable rock uplift rates
Comment upon the screw dislocation structure on HKUST-1 {111} surfaces
No full textElastic theory is used to propose an atomic scale structure for the screw dislocation core at the growth spiral seen on the {111} surface of the HKUST-1 metal-organic framework material. Diffusion across the dislocation core is predicted to be hindered whilst along the core, two possible structures are considered with contrasting effects upon the local chemical structure and transport properties
Climate forcing due to the 8200 cal yr BP event observed at Early Neolithic sites in the eastern Mediterranean
No full textWe explore the hypothesis that the abrupt drainage of Laurentide lakes and associated rapid switch of the North Atlantic thermohaline circulation 8200 yr ago had a catastrophic influence on Neolithic civilisation in large parts of southeastern Europe, Anatolia, Cyprus, and the Near East. The event at 8200 cal yr BP is observed in a large number of high-resolution climate proxies in the Northern Hemisphere, and in many cases corresponds to markedly cold and arid conditions. We identify the relevant archaeological levels of major Neolithic settlements in Central Anatolia, Cyprus, Greece and Bulgaria, and examine published stratigraphic, architectural, cultural and geoarchaeological studies for these sites. The specific archaeological events and processes we observe at a number of these sites during the study interval 8400–8000 cal yr BP lead us to refine some previously established Neolithisation models. The introduction of farming to South-East Europe occurs in all study regions (Thrace, Macedonia, Thessaly, Bulgaria) near 8200 cal yr BP. We observe major disruptions of Neolithic cultures in the Levant, North Syria, South-East Anatolia, Central Anatolia and Cyprus, at the same time. We conclude that the 8200 cal yr BP aridity event triggered the spread of early farmers, by different routes, out of West Asia and the Near East into Greece and Bulgaria
Crustal structure of the Hatton and the conjugate east Greenland rifted volcanic continental margins, NE Atlantic
No full textWe show new crustal models of the Hatton continental margin in the NE Atlantic using wide-angle arrivals from 89 four-component ocean bottom seismometers deployed along a 450 km dip and a 100 km strike profile. We interpret prominent asymmetry between the Hatton and the conjugate Greenland margins as caused by asymmetry in the initial continental stretching and thinning, as ubiquitously observed on “nonvolcanic” margins elsewhere. This stretched continental terrain was intruded and flooded by voluminous igneous activity which accompanied continental breakup. The velocity structure of the Hatton flank of the rift has a narrow continent-ocean transition (COT) only ∼40 km wide, with high velocities (6.9–7.3 km/s) in the lower crust intermediate between those of the continental Hatton Bank on one side and the oldest oceanic crust on the other. The high velocities are interpreted as due to intrusion of igneous sills which accompanied the extrusion of flood basalts at the time of continental breakup. The variation of thickness (h) and P wave velocities (vp) of the igneous section of the COT and the adjacent oceanic crust are consistent with melt formation from a mantle plume with a temperature ∼120–130°C above normal at breakup, followed by a decrease of ∼70–80°C over the first 10 Ma of seafloor spreading. The h-vp systematics are consistent with the dominant control on melt production being elevated mantle temperatures, with no requirement for either significant active small-scale mantle convection under the rift or of the presence of significant volumes of volatiles or fertile mantle
Transient permeability and reseal hardening in fault zones: evidence from dilation breccia textures
No full textt is well established that earthquake faulting can create permeability along a fault zone in high competence rocks - by mismatch of the fault walls and by secondary fracture in a surrounding damage zone - and that this permeability is created repeatedly during successive earthquake cycles. Less well proven is that such permeability is transient, being episodically reduced by precipitation of cements in the fracture porosity. The textures of carbonate dilation breccias, formed at around 1.7 km depth on the Dent Fault zone (NW England), lend support to this economically important concept of transient fracture permeability. The key observation is that many breccias reflect only a single episode of brecciation and reseal. A generally applicable explanation of such single-phase breccias is that they were resealed in the interval between major earthquakes, that this reseal made the breccia stronger that the intact rock, and that subsequent brecciation in the same rock volume was inhibited. This reseal-hardening model implies that transient permeability in fault zones may last no longer than the recurrence times of large earthquakes, and that the permeability conduits will change position in the damage zone with time, unless focused at a major fault jog or termination
Are we now living in the Anthropocene?
No full textIn 2002, Paul Crutzen, the Nobel Prize–winning chemist, sug-
gested that we had left the Holocene and had entered a new
Epoch—the Anthropocene—because of the global environ-
mental effects of increased human population and economic
development. The term has entered the geological literature
informally (e.g., Steffen et al., 2004; Syvitski et al., 2005; Cross-
land, 2005; Andersson et al., 2005) to denote the contemporary
global environment dominated by human activity. Here, mem-
bers of the Stratigraphy Commission of the Geological Society
of London amplify and extend the discussion of the effects
referred to by Crutzen and then apply the same criteria used to
set up new epochs to ask whether there really is justification or
need for a new term, and if so, where and how its boundary
might be placed
(Re)Reading The Origin
No full textCharles Darwin's 1859 book On the Origin of Species is much referenced, especially in this double anniversary year. But, does anyone still read it? And, if so, what is the book itself like as a text? We have asked biologists from a range of fields evolutionary biologists, but also geneticists, ecologists, paleontologists and molecular biologists to re-read (or read) The Origin for Current Biology. Below are the responses, contributed by: Andrew Berry, Matthew Cobb, Simon Conway Morris, Jerry Coyne, Hopi Hoekstra, Peter Lawrence, Robert May, Christiane Nüsslein-Volhard, Mark Ptashne, Matt Ridley and Marlene Zuk
A Neogene Chronology of Iceland Plume Activity from V-Shaped Ridges
No full textThe V-shaped ridges, which straddle the mid-oceanic ridges on either side of Iceland, are recognized as a window into transient convective circulation of the mantle. The geometry of these ridges places important constraints on the nature of asthenospheric flow within the head of the Icelandic plume. Associated changes in the bathymetry of the Greenland–Scotland Ridge may have modulated the overflow of North Atlantic Deep Water. In order to improve the Neogene chronology of these V-shaped ridges, we have re-analyzed a set of legacy seismic reflection profiles which cross the Reykjanes Ridge south of Iceland. After converting these profiles to depth, the sediment–basement interface was carefully picked and corrected for sediment loading. Ages were assigned using magnetic anomalies which were correlated to an astronomically tuned timescale. We then calculated the residual height of oceanic crust along each profile by removing components of long-wavelength subsidence which are caused by lithospheric plate cooling and by dynamic support of the plume. By correlating the pattern of residual height with free-air gravity anomalies, we can discriminate between the effects of normal faulting and crustal thickness variations. The pattern of residual height primarily reflects asthenospheric temperature fluctuations which flow away from the center of the Icelandic plume. If we assume that asthenospheric flow is radial, our results can be used to estimate the mass flux of the Icelandic plume which varies from 1–3 × 1014 kg/yr over the last 17 million years. Earlier, during Paleogene times, there is indirect evidence for higher mass flux. If the plume conduit beneath Iceland has a radius of 150 km, our inferred mass flux corresponds to an upwelling rate of 270 mm/yr. Finally, we have compared the Neogene record of residual height predicted for the Denmark Straits with estimates of the overflow of Northern Component Water, the Neogene precursor of North Atlantic Deep Water. There is a striking correlation between the two records over the last 5 million years which suggests that regional, plume-driven, vertical motion controlled deep-water overflow at the Denmark Straits
New information on Stokesosaurus, a tyrannosauroid (Dinosauria: Theropoda) from North America and the United Kingdom
No full textA partial postcranial skeleton from the Late Jurassic (Tithonian) of Dorset, England represents a new species of the theropod dinosaur Stokesosaurus, Stokesosaurus langhami. S. langhami is a member of Tyrannosauroidea, showing a distinct median vertical ridge on the lateral surface of the ilium, a prominent shelf medial to the preacetabular notch, a pronounced ischial tubercle, and a tibia that is elongate relative to the femur. One of only two definitive Jurassic tyrannosauroids known from more than isolated elements, it is the largest Jurassic tyrannosauroid reported to date and provides additional evidence for the presence of relatively small- or medium-sized basal tyrannosauroids in Asia, North
America, and Europe during the Late Jurassic. The occurrence of Stokesosaurus in the Tithonian of the UK and USA and the absence of tyrannosauroids in contemporaneous west African faunas supports the hypothesis of a paleobiogeographic link during the Late Jurassic between North America and Europe, to the exclusion of Africa