The depth of seismicity in the Kermanshah region of the Zagros Mountains (Iran)

A detailed microearthquake survey in a small region of the Zagros Mountains in Iran failed to detect any shocks whose depths were greater than 20 km. One third of the shocks in the same area have depths greater than 50 km when located using teleseismic observations. Because of poor azimuthal coverage and lack of local stations these teleseismic locations are probably in error. There is therefore no reliable seismic evidence for the existence of oceanic lithosphere beneath the Zagros fold belt.     

A viscoelastic relaxation model for post-seismic deformation from the San Francisco earthquake of 1906

We present a realistic model of the San Andreas fault zone. We propose that aseismic ground displacement is a sum of visco-elastic relaxation following large earthquakes, transient fault slip, steady fault slip and a large-scale relative plate motion. We used the model to explain the aseismic ground displacements observed after the San Francisco earthquake of 1906.The data do not resolve the question of which is the dominant mechanism, but viscoelastic relaxation can contribute a significant fraction of the displacement if the elastic plate thickness is 50 km or less. If the relative plate motion is taken to be 5.5 cm/yr, as found from plate rotation pole studies, then the zone of significant shearing in the mantle is probably at least 100 km thick beneath California.     

Sr-isotopic studies of the origin of the Morin anorthosite complex,Quebec, Canada

Rb-Sr isotopic investigations of the rock-types within the Morin anorthosite complex, Quebec, suggest that: 1. both the mangerites and the leuconorites and anorthosites within this complex crystallized with a range of ⁸⁷Sr/⁸⁶Sr ratios, and 2. at least some of the mangerites crystallized approximately 100 m.y. after the anorthosites and leuconorites. From this evidence, it is argued that a number of magma sources gave rise to the melts that formed these rocks and that some local hybridization of these melts also took place by assimilation of other rock types. This same pattern is found in the Adirondack and Nain Complexes.     

Melting of some alkaline-earth and transition-metal fluorides and alkali fluoroberyllates at elevated pressures: A search for melting systematics

The melting curves of the fluorides ZnF₂ and NiF₂ (rutile structure), CaF₂, SrF₂ and BaF₂ (fluorite structure), and of the fluoroberyllates Na₂BeF₄ and Li₂BeF₄ have been studied at pressures ? 40 kbar by differential thermal analysis in a piston-cylinder high-pressure device. The initial slopes (dT_m/dP)₀ of these melting curves are respectively 7.2, 5.8, 16.7, 15.2, 15.7, 15.1 and <0°C/kbar. A new Li₂BeF₄ polymorph, apparently of the olivine structure type, is stable at pressures > 10 kbar and its melting curve has an average slope of ～6.7°C/kbar. These new data and those for SiO₂, BeF₂, GeO₂, LiF and MgF₂, recently studied by Jackson, are combined with existing data for elements, ionic compounds and silicates to assess the influence of crystal structure, molar volume and the nature of interatomic bonding on the initial slopes of melting curves. It is found that the entropy of fusion (ΔS_m) is primarily a function of crystal structure while the volume change on fusion (ΔV_m) is controlled by crystal molar volume within each isostructural series. Such systematics have recently facilitated estimation of the initial slopes of the melting curves of periclase and stishovite. New and existing melting data for silicates and their analogues have been analysed and a systematic dependence of (dT_m/dP)₀ on SiO₂ concentration has been demonstrated. Possible implications of this trend for partial melting of upper-mantle garnet lherzolite are illustrated. Finally, the use of the traditional silicate-germanate and oxide-fluoride modelling schemes is reviewed in the light of information from this present study.     

Some aspects of the Castillo de Bellver oilspill

The Castillo de Bellver incident resulted in the loss of between 160 000 and 190 000 t of crude oil. Not only was this the largest spill to date in South Africa, but it occurred near an area of great ecological sensitivity, and in the vicinity of important commercial fishing grounds. Despite this, observations during the spill and on subsequent surveys indicated that environmental damage was minimal. This can only be attributed to the favourable direction of the wind, which caused the slick to move offshore and into the Benguela current, thus allowing for its natural dispersion. Some concern remains over oil still trapped in the sunken stern section.     

Ventifacts distribution in Qatar

This study attempts to investigate the distribution of ventifacts in Qatar. It is believed that ventifacts are confined to the areas within about 5 km of the Miocene or Mio-Pliocene Hofuf formations and the spreads of continental gravels derived from them. Three hypotheses were formulated: (1) Ventifacts in Qatar are confined to areas within about 5 km of the Hofuf formations and the spreads of continental gravels derived from them. The distribution of ventifacts within these areas varies according to the nature of the ground surface; (2) The most active ventifaction areas are where the continental gravels merge with the Eocene limestone because of the increase in saltation particle speed in these areas where bedrock or bare limestone is exposed; (3) The unit area ratio of ventifact to non-ventifact pebbles varies inversely with the total amount of pebbles. To test these hypotheses, nine land class categories were identified in the three major Hofuf formations. Line transects were carried out from randomly selected stations near the middle of the Hofuf formations. Along each transect systematic sampling was carried out at 200 m intervals. The data were processed using a WANG MVP 2200 computer with software developed for the project. It was found that ventifacts tend to concentrate on the outer edges of the continental gravels in areas of limestone outcrop and limestone pavement. Higher areas have big gravel counts and a low ratio of ventifacts while the low-lying plains have small gravel counts and a higher ratio of ventifacts. In certain areas ‘ventifact fields’ were found where the density of ventifacts was as high as 30 per m². Many of the ventifacts in these fields were buried beneath the surface suggesting that the ventifaction predates the present site conditions. Other high ventifact density areas were discovered where the ventifacts have collected in shallow depressions or hollows on the limestone plateaux. Water action has washed these ventifacts, a high proportion of which are dreikanters, into the hollows, where they have been partially buried in fine alluvial silts. These ‘ventifact graveyards’ are generally only a few metres wide but contain large numbers of fine specimens.     

Calculated geochronology and stress field orientations along the Hawaiian chain

A new method has been discovered for calculating ages of the main shield building stages of volcanoes along the Hawaiian chain from Kilauea to the Hawaiian-Emperor bend. The method is based on a graphical technique for hypothetical subtraction of distance intervals that theoretically represent regions of simultaneous volcanism along adjacent or nearly en-echelon loci of volcanism. Distances along the chain, measured from Kilauea, when progressively foreshortened by the distances of hypothetical “collapse” and plotted versus existing age data are found to give linear age-distance relationships. A calibration graph is presented that agrees closely with the measured ages in 17 of the 20 existing dated volcanoes. The criterion for simultaneous activity on different loci is based on the concept of equal azimuths of synchronous volcanic propagation within coeval segments of the chain. This is the predicted relationship when magmatic fluids inject the lithosphere along directions normal to a nearly horizontal least principal stress. It appears that the Pacific plate has been subjected to oscillatory, but principally clockwise, rotations of horizontal stress components during the last 40 m.y.     

Release of volatile mercury from soils and non-vascular plants

Vegetation plays a significant role in the biogeochemical cycling of mercury. This conclusion is drawn from data presented here on bioaccumulation and subsequent release of volatile mercury from non-vascular plants together with the results of previous work. There is no obvious relation between total plant Hg or soil Hg and rate of release from the plant. Heat of vaporization for Hg⁰ was calculated at 13.99 kcal/g-atom; from soil it was experimentally determined at 13.81 kcal/g-atom but from the most active vascular plant was only 9.49 kcal/g-atom.     

Oxygen isotopic ratios in fine quartz silt from sediments and soils of southern Africa

Fine quartz silt (1–10μm dia, important in aerosol dust) isolated from a large number of soils, as well as Phanerozoic shales, sandstones and recent sands of the southern African stratigraphie column (Carboniferous, Permian and Triassic) exhibits a mean δ¹⁸O of 12.2 ± 2.1%0. These values are similar to those reported for South Pacific pelagic sediments and adjacent land areas of similar latitude but are lower than those reported for this size fraction of 30 Mesozoic and Paleozoic shales (20.7 ± 1.8%.) and soils from mid-continental U.S.A., for aerosol quartz in the North Pacific pelagic sediments, and for eolian caps in high-elevation soils of Hawaii. The lower oxygen isotopic ratios in fine quartz silt of southern Africa reinforces the earlier indication that Southern Hemisphere detritai sedimentary reservoirs contain a higher proportion of igneous and metamorphic quartz (lower δ¹⁸O) and less lowtemperature authigenic quartz (higherδ¹⁸O) than Northern Hemisphere detritai sediments. The difference reflects climates, as continents drifted in latitude.     

Earth observations for sustainable development goals monitoring based on essential variables and driver-pressure-state-impact-response indicators

ABSTRACT

In recent years, researchers of different communities have increased their efforts in formalizing a set of measurements regularly collected for analysing changes in Drivers, States, Impacts and Responses of a given discipline. In some cases, different actors have converged in a minimum set of Essential Variables (EVs), such as for Climate, Biodiversity or Oceans. The definition of such EVs is an ongoing evolution and in extension (e.g. EVs for water) although some communities have not even started (e.g. agriculture and energy). This paper characterizes the Earth Observation (EO) networks and creates a graph representation of their relations. Secondly, this graph is enriched with the EVs produced by each network creating a knowledge base. Finally, an effort has been done to identify links between EVs and Sustainable Development Goals (SDG) indicators in a way that they indirectly connect the EO. An analysis to detect gaps in EO variables due to a lack of observational networks is performed. Several suggestions for improving SDG indicators framework by considering EVs are exposed, as well as proposing new necessary EVs and suggesting new EO based indicators. The complete graph is available in the ENEON website (http://www.eneon.net/graph-ev-sdg/).