Isophot Mapping Observations of Carbon Stars

Mapping observations have been made toward five carbon stars in the far-infrared using ISOPHOT, an imaging photo-polarimeter on board the Infrared Space Observatory. Cold, very extended dust shells are clearly revealed in two of them. Y CVn is surrounded by a very extended, detached dust shell, which indicates a sudden decline of the mass-loss by two orders of magnitude in the last (1-2) × 104 years on a short time scale. The Hipparcos parallax reinforces our previous conclusion that Y CVn is a J-type carbon star on the asymptotic giant branch. U Ant shows a double shell structure, a compact dust shell surrounded by a very extended one. The outer shell has a brightness comparable to the dust shell of Y CVn. The structure indicates that there were two different high mass-loss phases separated by a period with a much lower mass-loss rate in between the two. The structure is consistent with the double dust shell proposed for this star by Izumiura et al. (1997) based on a detailed investigation of IRAS survey data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Correction to: Mapping method of rainfall-induced landslide hazards by infiltration and slope stability analysis

Landslides - A Correction to this paper has been published: https://doi.org/10.1007/s10346-021-01642-4     

A large hydrothermal reservoir beneath Taal Volcano (Philippines) revealed by magnetotelluric resistivity survey: 2D resistivity modeling

Taal Volcano, located in the southwestern part of Luzon Island, Philippines, has frequently experienced catastrophic eruptions from both the Main Crater on Volcano Island and flank eruptions. These eruptions have been magmatic, phreatomagmatic, and hydrothermal, with the latter implying the existence of a large-scale hydrothermal system beneath the volcano. We conducted an electrical resistivity survey using the magnetotelluric method in order to identify the location and geometry of the hydrothermal reservoir and sealing cap rock. Two-dimensional inversion using the observed data indicates four similar resistivity sections. The structure at shallow depths corresponds to volcanic deposits and an aquifer. Below 1 km, the structure features a relatively resistive zone beneath the main crater surrounded by a conductive shell. We interpreted these to be a large hydrothermal reservoir with an impermeable cap rock sealing it. Recent ground deformation detected by GPS measurements suggests that the hydrothermal reservoir is active. The interpreted cap rock thins just beneath the main crater and could easily be destroyed by an imbalance in the hydrothermal system. We conclude that this hydrothermal reservoir plays a significant role in driving catastrophic eruptions that begin with a hydrothermal explosion at the main crater.     

Congruence between euphausiid community and water region in the northwestern Pacific: particularly in the Oyashio–Kuroshio Mixed Water Region

The relationship between euphausiid community structure and water region was studied during a 2-year seasonal survey in the northwestern (NW) Pacific Ocean. The euphausiid community structure and its associated species were analyzed from 38 micronekton samples collected during eight cruises. The euphausiid community structure and its distribution patterns clearly corresponded to physical oceanographic features in the Oyashio region, Oyashio–Kuroshio Mixed Water Region (OKMWR), and Kuroshio region. In contrast, community structure was unrelated to seasonality. The 19 species out of 40 identified in this area were grouped and named after their habitats. The six cold-water species were grouped into three regional types: two coastal Oyashio species, three Oyashio–OKMWR species, and one Oyashio–Kuroshio species. The four species dominating in the OKMWR were categorized into each specific types: Nematoscelis difficilis as OKMWR–Oyashio species, Euphausia gibboides as OKMWR species, Euphausia similis as OKMWR–Oyashio & OKMWR–Kuroshio species, and Euphausia recurva as OKMWR–Kuroshio species. The seven warm-water species were categorized as Kuroshio–OKMWR species or Kuroshio species. The other two species were categorized as cosmopolitan species. In particular, regarding the result in the OKMWR, our study suggest that (1) the OKMWR has high species diversity, and (2) the dominant species, such as Euphausia pacifica, N. difficilis, E. similis, and E. gibboides, are considered to be key species in the food webs in this region.     

Hydrodynamic characteristics of the Tam Pokhari glacial lake outburst flood in the Mt. Everest region,Nepal

The Tam Pokhari glacial lake outburst flood (GLOF), which occurred in 1998 in the Mt. Everest region of Nepal, was evaluated using hydrodynamic models to gain a better understanding of the flow behaviour. The flood wave was analysed separately under rigid and erodible boundary conditions. In both cases, the calculated dam‐breach hydrograph, which had a peak discharge of about 10 000 m³/s, was routed through the Inkhu River, which originates from the lake. The morphologic changes along the river were also analysed and the results were compared with satellite images, field observations and recorded data. In the case of rigid boundaries, the routing procedure gradually attenuated the peaks of the hydrographs to account for hydraulic pooling in narrow gorges and storage in the channel. In the case of erodible boundaries, such effects were minimized due to the increment in channel capacity associated with erosion by debris flow. The study revealed that the GLOF event produced a large‐scale debris flow. Additionally, the results revealed that erosion and deposition took place intermittently, but that approximately 440 000 m³ of sediment was deposited about 14 km downstream from the lake mouth. The calculated peak of the water and sediment mixture at 14·4 km was found to be 30 000 m³/s, which is almost 6 times as large as that observed when the rigid boundary conditions were used. Further, the increase in the peaks of the hydrographs due to sediment transport was the primary reason for the destruction associated with the GLOF. These findings suggest that the local sedimentology and topography, as well as other geo‐hazard conditions in the area, should be carefully evaluated before recommending any control measures against GLOFs in the Himalayan region. Copyright © 2009 John Wiley & Sons, Ltd.     

An Application of Hydraulic Tomography to a Large‐Scale Fractured Granite Site,Mizunami, Japan

While hydraulic tomography (HT) is a mature aquifer characterization technology, its applications to characterize hydrogeology of kilometer‐scale fault and fracture zones are rare. This paper sequentially analyzes datasets from two new pumping tests as well as those from two previous pumping tests analyzed by Illman et al. (2009) at a fractured granite site in Mizunami, Japan. Results of this analysis show that datasets from two previous pumping tests at one side of a fault zone as used in the previous study led to inaccurate mapping of fracture and fault zones. Inclusion of the datasets from the two new pumping tests (one of which was conducted on the other side of the fault) yields locations of the fault zone consistent with those based on geological mapping. The new datasets also produce a detailed image of the irregular fault zone, which is not available from geological investigation alone and the previous study. As a result, we conclude that if prior knowledge about geological structures at a field site is considered during the design of HT surveys, valuable non‐redundant datasets about the fracture and fault zones can be collected. Only with these non‐redundant data sets, can HT then be a viable and robust tool for delineating fracture and fault distributions over kilometer scales, even when only a limited number of boreholes are available. In essence, this paper proves that HT is a new tool for geologists, geophysicists, and engineers for mapping large‐scale fracture and fault zone distributions.     

Quasi-Static Strain and Stress Fields due to a Moment Tensor in Elastic–Viscoelastic Layered Half-Space

We derived explicit expressions in the time domain for 3-D quasi-static strain and stress fields, due to a point moment tensor source in an elastic surface layer overlying viscoelastic half-space under gravity. The expressions of strain in the elastic surface layer were directly obtained from the expressions of displacement in our previous paper. The conversion of strain into stress is easy, because the stress–strain relation of elastic material is linear. In the viscoelastic substratum, the expressions of strain were obtained by applying the correspondence principle of linear viscoelasticity to the associated elastic solution. The strain–stress conversion is not straightforward, as the stress–strain relation of viscoelastic material is usually given in a differential form. To convert strain into stress, we used an integral form of the stress–strain relation instead of the usual differential form. The expressions give the responses of elastic half-space at \( t = 0 \) , and the responses of an elastic plate floating on non-viscous liquid at \( t = \infty \) . The moment tensor is rationally decomposed into the three independent force systems, corresponding to isotropic expansion, shear faulting and crack opening, and so the expressions include the strain and stress fields for these force systems as special cases. As the first numerical example, we computed the temporal changes in strain and stress fields after the sudden opening of an infinitely long vertical crack cutting the elastic surface layer. Here, we observe that the stress changes caused by the sudden crack opening gradually decay with time and vanish at \( t = \infty \) everywhere. After the completion of stress relaxation, a characteristic pattern of shear strain remains in the viscoelastic substratum. Since the strain and stress fields at \( t = \infty \) can be read as the strain- and stress-rate fields caused by steady crack opening, respectively, this numerical example demonstrates the realization of a steady stress state supported by steady viscous flow in the asthenosphere, associated with steady seafloor spreading at mid-ocean ridges. For the second numerical example, we computed the temporal changes in strain and stress fields after the 2011 Tohoku-oki mega-thrust earthquake, which occurred at the North American-Pacific plate interface. In this numerical example, the stress changes caused by coseismic fault slip vanish at \( t = \infty \) in the viscoelastic substratum, but remain in the elastic surface layer. The coseismic stress changes (and also strain changes) in the elastic surface layer diffuse away from the source region with time, due to gradual stress relaxation in the viscoelastic substratum.     

Tsunami hazard evaluation for Kuwait and Arabian Gulf due to Makran Subduction Zone and Subaerial landslides

Given the recent historical disastrous tsunamis and the knowledge that the Arabian Gulf (AG) is tectonically active, this study aimed to evaluate tsunami hazards in Kuwait from both submarine earthquakes and subaerial landslides. Despite the low or unknown tsunami risks that impose potential threats to the coastal area’s infrastructures and population of Kuwait, such an investigation is important to sustain the economy and safety of life. This study focused on tsunamis generated by submarine earthquakes with earthquake magnitudes (M _w ) of 8.3–9.0 along the Makran Subduction Zone (MSZ) and subaerial landslides with volumes of 0.75–2.0 km³ from six sources along the Iranian coast inside the AG and one source at the Gulf entrance in Oman. The level of tsunami hazards associated with these tsunamigenic sources was evaluated using numerical modeling. Tsunami model was applied to conduct a numerical tsunami simulation and predict tsunami propagation. For landslide sources, a two-layer model was proposed to solve nonlinear longwave equations within two interfacing layers with appropriate kinematic and dynamic boundary conditions. Threat level maps along the coasts of the AG and Kuwait were developed to illustrate the impacts of potential tsunamis triggered by submarine earthquakes of different scales and subaerial landslides at different sources. GEBCO 30 arc-second grid data and others were used as bathymetry and topography data for numerical modeling. Earthquakes of M _w 8.3 and M _w 8.6 along the MSZ had low and considerable impacts, respectively, at the Gulf entrance, but negligible impacts on Kuwait. An earthquake of M _w 9.0 had a remarkable impact for the entire Gulf region and generated a maximum tsunami amplitude of up to 0.5 m along the Kuwaiti coastline 12 h after the earthquake. In the case of landslides inside the AG, the majority impact occurred locally near the sources. The landslide source opposite to Kuwait Bay generated the maximum tsunami amplitudes reaching 0.3 m inside Kuwait Bay and 1.8 m along the southern coasts of Kuwait.

     

http://dx.doi.org/10.1016/j.gsf.2016.06.013

The Archean continental crusts account for ca.20% of the present volume,but the thermal history of the Earths' mantle suggests much more continental crusts were formed in the early Archean.Because the Archean continental crust underwent severe metamorphism,it is important to avoid influence by the later thermal events.We carried out a comprehensive geochronological work of Cathodoluminescence(CL) observation and U-Pb dating of zircons from orthogneisses and supracrustal rocks over the Saglek Block to obtain their protolith ages.The zircons were classified into three domains of core,mantle and rims,and the cores were further classified into three groups of inherited,altered and zoned cores based on the zonation on the CL images.We estimated the protolith ages from Pb-Pb ages of the zoned-cores of zircons with low U contents.We made a detailed sketch of a small outcrop in St.John's Harbour South(SJHS) area,and classified the orthogneisses and mafic enclaves into seven generations based on the geologic occurrence.The first and second generations comprise mafic rocks and lack magmatic zircons.We conducted CL imaging and U-Pb dating of zircons from the third,sixth and seventh generation of the orthogneisses to estimate the protolith ages at 3902 L 25,3892 ± 33 and 3897 ± 33 Ma for each,supporting the presence of the over 3.9 Ca Iqaluk Gneiss.The geological occurrence that the mafic rocks occur as enclaves within the 3.9 Ga Iqaluk Gneiss indicates that they are the oldest supracrustal rocks in the world.Our geochronological and geological studies show the Uivak Gneiss is quite varied in lithology and age from 3.6 to 3.9 Ga,and tentatively classified into six groups based on their ages.The oldest Uivak Gneiss components including the Iqaluk Gneiss are present around the SJHS area,and the orthogneisses become young as it is away.The lines of evidence of overprinting of younger granitoid on older granitoid in small outcrops and geological-map scale as well as presence of inherited zircons even in the oldest suite suggests that crustal reworking played an important role on erasing the ancient crusts.     

Hemispheric distributions of HCl above and below the Venus’ clouds by ground-based 1.7 μm spectroscopy

The abundance of hydrogen chloride (HCl) in the Venus atmosphere was measured by ground-based IR spectroscopy. The dayside measurements were performed in May 2007 with a resolution of 40,000, and the nightside measurements in October 1999 with a resolution of 1000. The hemispheric distributions of the HCl mixing ratio measured above the Venus’ clouds show no significant structure with a disc-averaged value of 0.74±0.06 ppm which is in the similar range as the previous report of 0.6±0.2 ppm. The representative height for the dayside measurements is estimated to be 60-66 km. Recent results by Venus Express/SPICAV/SOIR show much smaller values of 0.1-0.2 ppm at 64-94 km; however the direct comparison is difficult due to the different spatial conditions. The hemispheric distributions of the ³⁵Cl/³⁷Cl isotope ratio are also found to show no significant structure with a disc-averaged value of 3.1±0.4 which coincides with the terrestrial value of 3.1. The HCl mixing ratios below the clouds are also found to show no significant structure with a disc-averaged value of 0.40±0.05 ppm, which is similar to the previous reports of 0.4-0.5 ppm. The larger HCl mixing ratio above the clouds than below suggests the production of HCl in the cloud region or above. Also, a uniform hemispherical distribution of H₂O is found below the clouds with a disc-averaged mixing ratio of 25±5 ppm; this is in the same range as the previous measurements. Those uniform distributions of HCl and H₂O support the fact that their chemical lifetimes are much longer than that of mixing as has been discussed so far.