Tsunami threat in the Indian Ocean from a future megathrust earthquake west of Sumatra

Several independent indicators imply a high probability of a great (M > 8) earthquake rupture of the subduction megathrust under the Mentawai Islands of West Sumatra. The human consequences of such an event depend crucially on its tsunamigenic potential, which in turn depends on unpredictable details of slip distribution on the megathrust and how resulting seafloor movements and the propagating tsunami waves interact with bathymetry. Here we address the forward problem by modelling about 1000 possible complex earthquake ruptures and calculating the seafloor displacements and tsunami wave height distributions that would result from the most likely 100 or so, as judged by reference to paleogeodetic data. Additionally we carry out a systematic study of the importance of the location of maximum slip with respect to the morphology of the fore-arc complex. Our results indicate a generally smaller regional tsunami hazard than was realised in Aceh during the December 2004 event, though more than 20% of simulations result in tsunami wave heights of more than 5 m for the southern Sumatran cities of Padang and Bengkulu. The extreme events in these simulations produce results which are consistent with recent deterministic studies. The study confirms the sensitivity of predicted wave heights to the distribution of slip even for events with similar moment and reproduces Plafker's rule of thumb. Additionally we show that the maximum wave height observed at a single location scales with the magnitude though data for all magnitudes exhibit extreme variability. Finally, we show that for any coastal location in the near field of the earthquake, despite the complexity of the earthquake rupture simulations and the large range of magnitudes modelled, the timing of inundation is constant to first order and the maximum height of the modelled waves is directly proportional to the vertical coseismic displacement experienced at that point. These results may assist in developing tsunami preparedness strategies around the Indian Ocean and in particular along the coasts of western Sumatra.     

Fission track dating obsidians in Central and Northern Anatolia

Twenty obsidian samples from Central and North Anatolia were dated by the fission track method. Split samples analyzed in two different laboratories give consistent results. Data presented refer to three volcanic fields and are summarized as follows: Orta-Sakaeli (Northern Anatolia) obsidians with ages from 21–23 Ma; Göllü Dagi dome complex near Çiftlik (Central anatolia) has given ages between 1.33–0.98 Ma; Acigöl caldera (Central Anatolia) shows three age groups: (1) Eruptions of precaldera (Bogazköy) obsidians with ages 0.18–0.15 Ma; (2) Formation of the large intracaldera dome Kocadag-Taskesiktepe at about 0.08 Ma (uncorrected apparent age of 0.075 Ma); and (3) Acigöl peripheral obsidian domes with plateau ages of 0.020 and 0.019 Ma, and an additional uncorrected age of 0.018 Ma form a distinct age group. This fission track parameters discriminate between the various obsidian sources of prehistoric obsidian artifacts.     

New estimations of precipitation and surface sublimation in East Antarctica from snow accumulation measurements

Surface mass balance (SMB) distribution and its temporal and spatial variability is an essential input parameter in mass balance studies. Different methods were used, compared and integrated (stake farms, ice cores, snow radar, surface morphology, remote sensing) at eight sites along a transect from Terra Nova Bay (TNB) to Dome C (DC) (East Antarctica), to provide detailed information on the SMB. Spatial variability measurements show that the measured maximum snow accumulation (SA) in a 15 km area is well correlated to firn temperature. Wind-driven sublimation processes, controlled by the surface slope in the wind direction, have a huge impact (up to 85% of snow precipitation) on SMB and are significant in terms of past, present and future SMB evaluations. The snow redistribution process is local and has a strong impact on the annual variability of accumulation. The spatial variability of SMB at the kilometre scale is one order of magnitude higher than its temporal variability (20–30%) at the centennial time scale. This high spatial variability is due to wind-driven sublimation. Compared with our SMB calculations, previous compilations generally over-estimate SMB, up to 65% in some areas.     

Impact of human activities on the central Mediterranean offshore: Evidence from Hg distribution in box-core sediments from the Ionian Sea

Total Hg concentrations have been measured for five box-core sediments collected seawards of the Augusta industrial area (SE Sicily). In more coastal sediments, upcore increasing Hg concentrations, exceeding the Hg background concentration estimated for the Strait of Sicily, indicate Hg contamination over time due to the industrial area development. Strong correlation between total organic C (TOC) and Hg concentrations was found only for core BX2, that displays organic C to total N (C/N) ratios indicative of autochthonous organic matter. For other sediments, high Hg enrichment factors with respect to TOC indicate, in addition to Hg trapping by TOC, other factors as responsible for Hg accumulation. In the presence of some contribution of detrital organic matter, Hg is mainly adsorbed onto the mineral component of the bottom sediments probably because TOC is saturated by Hg excess. Contaminant impact affected also the open sea environment. Main drivers of Hg flux towards the offshore were dredged materials, which repeatedly discharged sediment, resulting in substantial increases in TOC contents and high C/N ratios. Consistent with the geochemistry of recent turbidites, these anomalous sedimentary inputs induced sediment redox environment modifications, constrained by Mn peaks, which affected Hg distribution.     

Petrology of Karoo volcanic rocks in the southern Lebombo monocline, Mozambique

The Karoo volcanic sequence in the southern Lebombo monocline in Mozambique contains different silicic units in the form of pyroclastic rocks, and two different basalt types. The silicic units in the lower part of the Lebombo sequence are formed by a lower unit of dacites and rhyolites (67–80 wt.% SiO₂) with high Ba (990–2500 ppm), Zr (800–1100 ppm) and Y (130–240 ppm), which are part of the Jozini–Mbuluzi Formation, followed by a second unit, interlayered with the Movene basalts, of high-SiO₂ rhyolites (76–78 wt.%; the Sica Beds Formation), with low Sr (19–54 ppm), Zr (340–480 ppm) and Ba (330–850 ppm) plus rare quartz-trachytes (64–66 wt.% SiO₂), with high Nb and Rb contents (240–250 and 370–381 ppm, respectively), and relatively low Zr (450–460 ppm). The mafic rocks found at the top of the sequence are basalts and ferrobasalts belonging to the Movene Formation. The basalts have roughly flat mantle-normalized incompatible element patterns, with abundances of the most incompatible elements not higher than 25 times primitive mantle. The ferrobasalt has TiO₂  4.7 wt.%, Fe₂O_3t = 16 wt.%, and high Y (100 ppm), Zr (420 ppm) and Ba (1000 ppm). The Movene basalts have initial (at 180 Ma) ⁸⁷Sr/⁸⁶Sr = 0.7052–0.7054 and ¹⁴³Nd/¹⁴⁴Nd = 0.51232, and the Movene ferrobasalt has even lower ⁸⁷Sr/⁸⁶Sr (0.70377) and higher ¹⁴³Nd/¹⁴⁴Nd (0.51259). The silicic rocks show a modest range of initial Sr-(⁸⁷Sr/⁸⁶Sr = 0.70470–0.70648) and Nd-(¹⁴³Nd/¹⁴⁴Nd = 0.51223–0.51243) isotope ratios. The less evolved dacites could have been formed after crystal fractionation of oxide-rich gabbroic cumulates from mafic parental magmas, whereas the most silica-rich rhyolites could have been formed after fractional crystallization of feldspars, pyroxenes, oxides, zircon and apatite from a parental dacite magma. The composition of the Movene basalts imply different feeding systems from those of the underlying Sabie River basalts.     

On the role of the cosmological constant in the formation of neutrino halos

We investigate the role of the cosmological constant in the formation of neutrino halos. Using the observational limit 10^–55 cm^–2 we find that it is relevant only for neutrinos of very light rest-mass: namely, 10^–1 eV.On leave of absence from Department of Physics, College of Mines, Ostrava, Czechoslovakia.     

遥感定量反演地表参数对于气候变化的响应研究

遥感定量反演地表参数时间序列产品已被广泛应用于植被动态变化、全球气候变化、防灾减灾及环境保护等领域。由于卫星观测往往受到大气条件（如云、气溶胶、水汽等）以及传感器自身稳定性的影响等,许多由卫星观测反演得到的陆表产品,如归一化差值植被指数（NDVI）、叶面积指数（LAI）、地表温度（LST）、微波极化亮温（PDBT）等存在严重的时空不连续问题。为了获取时间序列上连续、空间上完整的地表参数遥感产品以满足长时序的陆面过程分析与建模的需求,目前已发展多种遥感时间序列重建模型。本文介绍了基于傅里叶变换的时间序列谐波分析（HANTS）方法,能够识别并去除受到云和大气影响的像元（噪声）,对原始时序数据进行时间插值来重建连续时间序列的数据,并针对其面向多种不同时空尺度的遥感反演地表参数以及在非洲、南美洲、欧洲、中国及印度等全球不同地区的应用研究进行了综述,包括植被动态变化对于气候变化及流域水循环过程的响应、干旱监测、基于土壤含水量饱和度时间序列分析的洪涝灾害易发区监测、遥感估算地表蒸散发时间尺度扩展等方面的研究,充分阐释了遥感时间序列产品在地气相互作用的各类研究领域的应用。