South Flank Research Articles

고해상도 기후변화 시나리오 자료를 활용한 한라산 지역 기온 및 기후대 변화 전망

The purpose of this study is to quantify the magnitudes of projected 21st century temperature changes and shifting climate zones over Mt. Halla, Korea based on high-resolution (1km×1km) climate change scenario data sets down-scaled from a global climate model (HadGEM2-AO) simulations using PRIDE (PRISM based Downscaling Estimation Model) as well as the simulations of a Regional Climate Model (RCM; HadGEM3-RA). The high resolution climate data demonstrate that the magnitudes of increases in coldest and warmest monthly mean temperatures over Mt. Halla will exceed those of the averages across the Korean Peninsula during the 21st century, leading to the shifts of climate zones. The isoline with 5°C (20°C) of the coldest (warmest) monthly average temperature associated with sub-tropical (sub-alpine) climate zones will migrate from 100~230m (950~1,300m) to 300~500m (1,300~1,600m) of altitude in the late 21st century (2071~2100) under the RCP 4.5 scenario. These changes are expected to be more obviously observed in the south flank of Mt. Halla as well as under the RCP 8.5 scenario. These results indicate that changes in climate zones will lead to the extinction of sub-alpine ecosystems over Mt. Halla due to increases of summertime heat stress as well as to the expansion of the sub-tropical forest zone toward mid-mountain regions due to reduction of wintertime stress in the warmer 21st century.

Depositional processes of alluvial fans along the Hilina Pali fault scarp, Island of Hawaii

A series of previously unstudied alluvial fans are actively forming along the Hilina Pali escarpment on the south flank of Kīlauea volcano on the Island of Hawaii. These fans are characterized by their steep slopes, coarse grain sizes, and lobate surface morphology. Fans are fed by bedrock channels that drain from the Ka'ū Desert, but sediment is mostly sourced from deeply eroded alcoves carved into the Hilina Pali. Examination of recent deposits indicates that the fans are dominantly constructed from gravel and larger sized sediment. Flow discharges calculated using field measurements of channel geometries and the Manning equation indicate that events inducing sediment transport are of high magnitude and occur during high intensity precipitation events, including Kona storms. The fans along the Hilina Pali appear to be a rare example of fans formed predominately from sieve lobe deposition owing to the area's high slopes, high discharge, coarse bedload, and limited supply of fine-grained sediment. Given such conditions, sieve lobe deposition can form large lobes consisting of boulder-sized material, which may have implications for the identification of depositional processes when interpreting the stratigraphic record.

South Flank of the Yangtze Delta: Past, present, and future

Chenier plain and mudflat development in the South Flank of the Yangtze Delta are examined by multi-disciplinary methods over different spatiotemporal scales and changing human-earth interactions. The study site contains a narrow belt of elongated ridge complexes that formed along the sediment-deficient open coast from 6500 to 4000yr BP. Since then and until the past two decades, shoreline progradation has accelerated due to increasing sediment supply, fueling rapid deltaic expansion. Superimposed on this trend are a series of discrete sand-dominated ridges deposited during several stormy intervals. Tidal flat development is regulated by complex estuarine processes. Short-term morphodynamic variations at the site are caused by the alternations of tides and waves, while intermediate morphodynamic variations are controlled by the multi-decadal shifting of river stem channel and stormy climates. The ongoing rapid accretion on the tidal flats is predicted to continue into the near future because the estuarine buffer effect is expected to balance the adverse impacts of decreasing riverine sediment discharge and rising sea level. Technological developments during the last ~2000years are exemplified by seawall construction against sea flooding, marking a transition from passive to active. Dike construction has been used more frequently and intensively to reclaim land since the 1970s, in support of the booming socioeconomic development in the region. Lessons from complex morphodynamic change and human-earth interactions in the Southern Yangtze Delta admonish us to not reclaim coastal wetland by lower-flat enclosures (constructing new dikes near the low waterline), while an optimal alternative would be to implement upper-flat enclosures (constructing new dikes around the high waterline) on the continuously accretionary tidal flats, with auxiliary biological restoration engineering, to satisfy both socioeconomic development and sustainable wetland conservancy.

The transtensional offshore portion of the northern San Andreas fault: Fault zone geometry, late Pleistocene to Holocene sediment deposition, shallow deformation patterns, and asymmetric basin growth

We mapped an ~120 km offshore portion of the northern San Andreas fault (SAF) between Point Arena and Point Delgada using closely spaced seismic reflection profiles (1605 km), high-resolution multibeam bathymetry (~1600 km 2 ), and marine magnetic data. This new data set documents SAF location and continuity, associated tectonic geomorphology, shallow stratigraphy, and deformation. Variable deformation patterns in the generally narrow (∼1 km wide) fault zone are largely associated with fault trend and with transtensional and transpressional fault bends. We divide this unique transtensional portion of the offshore SAF into six sections along and adjacent to the SAF based on fault trend, deformation styles, seismic stratigraphy, and seafloor bathymetry. In the southern region of the study area, the SAF includes a 10-km-long zone characterized by two active parallel fault strands. Slip transfer and long-term straightening of the fault trace in this zone are likely leading to transfer of a slice of the Pacific plate to the North American plate. The SAF in the northern region of the survey area passes through two sharp fault bends (∼9°, right stepping, and ∼8°, left stepping), resulting in both an asymmetric lazy Z–shape sedimentary basin (Noyo basin) and an uplifted rocky shoal (Tolo Bank). Seismic stratigraphic sequences and unconformities within the Noyo basin correlate with the previous 4 major Quaternary sea-level lowstands and record basin tilting of ∼0.6°/100 k.y. Migration of the basin depocenter indicates a lateral slip rate on the SAF of 10–19 mm/yr for the past 350 k.y. Data collected west of the SAF on the south flank of Cape Mendocino are inconsistent with the presence of an offshore fault strand that connects the SAF with the Mendocino Triple Junction. Instead, we suggest that the SAF previously mapped onshore at Point Delgada continues onshore northward and transitions to the King Range thrust.

Treeline and timberline dynamics on the northern and southern slopes of the Retezat Mountains (Romania) during the late glacial and the Holocene

To investigate treeline and timberline dynamics in the Retezat Mountains (Romanian Carpathians), late glacial and Holocene sediment sequences from four lakes were studied. The south and north slopes of the mountain range were compared using two lakes from the north flank (Lake Brazi, 1740 m a.s.l. and Lake Gales, 1990 m a.s.l) and two from the south flank (Lake Lia, 1910 m a.s.l. and Lake Bucura, 2040 m a.s.l.). Macrofossil and stomata analyses were performed to assess changes in the local vegetation, supplemented by pollen, charcoal and loss-on-ignition analyses.Our results show that treeline reached Lake Brazi on the northern side during the late glacial (ca. 14,000 cal yr BP) and then Lake Gales between 11,000 and 10,800 cal yr BP. During the early Holocene the upper limit of closed forest, the timberline, reached and passed Lake Brazi and has stayed above it since, but it has never reached Lake Gales at 1990 m a.s.l. The expansion of Larix decidua in the late glacialand early Holocene around Lake Brazi is unique. Stomata and macrofossils of Abies alba are also more abundant in the northern records.On the southern flank, treeline reached Lake Lia at around 12,000 cal yr BP, and was either very close to or at the elevation of Lake Bucura between ca. 8600 and 3000 cal yr BP. Timberline reached Lake Lia at ca. 8000 cal yr BP, some 3000 years after Lake Brazi, only 170 m lower on the north slope. Local fire events delayed the advance of timberline around Lake Lia in the early Holocene in a dry continental climate. The surrounding forest was dominated by Picea abies with individuals of Pinus cembra and stands of P. mugo until about 3000 cal yr BP when timberline retreated below the lake.Maximum elevation of timberline was attained between ca. 8000 and 3000 cal yr BP, after which it descended in response to climate cooling.Regional climate change appears to be the main driver of treeline dynamics, but it was modified by local climatic differences due to slope aspect. The first signs of human disturbance appeared ca. 4200 cal yr BP, when naturally open areas were used as alpine pastures. Human impact in the treeline ecotone, mainly burning and grazing, was intensified after ca. 2600 cal yr BP, contributing to the widening of the ecotone and the lowering of the timberline.

The evolution characteristics of main waterways and their control mechanism in the radial sand ridges of the southern Yellow Sea

The comparison of the underwater topographic data in recent four decades shows that main waterways of the radial sand ridges area in the southern Yellow Sea tend to gradually migrate southward (scour depth and southward extension of the main channels in Xiyang, southward approach of Lanshayang Waterway and Xiaomiaohong Waterway on South Flank). Although there are various hypotheses about the cause and mechanism of the overall southward migration of the radial sand ridges, no universal and reliable understanding has been obtained so far. The mechanism of this process becomes a challenging problem which serves a key issue in the morphodynamics of the radial sand ridges and the harbor construction in this area. On the basis of the shoreline positions and underwater terrains at different development stages of the Huanghe Delta coast in northern Jiangsu Province, China since the northward return of the Huanghe River and flowed into the Bohai Sea, combined with the tidal wave numerical simulation study, the characteristics and hydrodynamic changes of the tidal wave system in the southern Yellow Sea at different evolution stages are investigated. It is shown that due to the shoreline retreat and the erosion of underwater delta, tidal current velocity is enhanced, and the enhanced area gradually migrates southward. It is revealed that this southward migration of a large-scale regional hydrodynamic axis is possibly a dominant mechanism leading to the overall southward migration of the radial sand ridges.

Determination of petrophysical properties of sedimentary rocks by optical methods

Petrophysical properties of rocks (thermal diffusivity and conductivity, porosity and density) as well as the correlation between them are of great importance for many geoscientific applications. The porosity of the reservoir rocks and their permeability are the most fundamental physical properties with respect to the storage and transmission of fluids, mainly oil characterization. Accurate knowledge of these parameters for any hydrocarbon reservoir is required for efficient development, management, and prediction of future performance of the oilfield. Thus, the porosity and permeability, as well as the chemical composition must be quantified as precisely as possible. This should be done along with the thermal properties, density, conductivity, diffusivity and effusivity that are intimately related with them. For this reason, photothermal Beam Deflection Spectrometry (BDS) technique for determination of materials' thermal properties together with other methods such as Energy Dispersive X-ray Scanning Electron Microscopy (SEM-EDX) for determining the chemical composition and sample structure, as well as optical microscopy to determine the particles size, were applied for characterization of sedimentary rocks. The rocks were obtained from the Andes south flank in the Venezuela's western basin. The validation of BDS applicability for determination of petrophysical properties of three sedimentary rocks of different texture and composition (all from Late Cretaceous associated with the Luna, Capacho and Colón-Mito Juan geological formations) was performed. The rocks' thermal properties were correlated to the microstructures and chemical composition of the examined samples.

Microfacies and Morphotectonic of the Tirgan Formation in Ghorogh Syncline (North of Chenaran)

In this research, the Tirgan Formation in Ghorogh Syncline (north of Chenaran) with the thickness of 412 m in north flank and 251 m in south flank is studied. The Tirgan Formation in Ghorogh sectionsis included limestones, marlylimestones, shales and sandstones in lower parts of the formation. In these sections, there are impressions of echinoderms toxasteridae family, many of foraminifera from orbitolinidae family and also lots of calcareous algae that create facies variation along with other nonskeletal allochems. The study of sediment facies led to the recognition of four facies belts and six microscopic standard facies in the Tirgan Formation and shows the oscillation of sea level but totally it can be concluded that the basin was shallow and formed in the ramp platform. According to the evidence, the oolithic limestones and intercalated shales of the Tirgan Formation in south flank, Ghorogh Syncline are slided on the red sandstone of Shurijeh Formation as transition slides because of lubrication. These landslides are distinguished and formed (7times) because of the stresses which are done from the northern syncline to the south of Ghorogh valley and formed the current morphotectonic for the area. This phenomenon could name as decollement.

Benthic Foraminiferal and Calcareous Algae Assemblages in the Tirgan Formation (Urgonien Facies Type) in South Flank of Ghorogh Syncline (North of Chenaran), NE Iran

In this research, the Tirgan Formation in the south flank of Ghorogh Syncline (north of Chenaran), northeastern Iran with the thickness of 251 was studied. This section consists of limestone, marly limestone and shale with impressions of echinoderms toxasteridae family, many of foraminifera from orbitolinidae family and also lots of calcareous algae that create facies variation along with other non-skeletal allochems. Micropaleontological investigation has been carried out on 90 thin-sections. These criteria reveal that an equivalent of the Urgonian facies type (in France-Swiss area) and open marine, low depth sedimentary basin are extended in the Kopet-Dagh basin. In this article, we tried to introduce some of the important foraminiferal and calcareous algal assemblages of this area.

Los primeros geólogos de YPF en Comodoro Rivadavia y sus aportes en la región del Golfo San Jorge

Entre 1908 y 1922 Stappenbeck, Schiller, Keidel, Wichmann y Windhausen trabajaron en la zona por cuenta de la Dirección de Minas y Geología. En 1922 se creó Yacimientos Petrolíferos Fiscales, YPF, y se nombró al frente de la División Geología al italiano Guido Bonarelli. En 1925 llegó el italiano Egidio Feruglio a la recién creada Sección Geología de Comodoro Rivadavia. En 1926 se incorporó el ruso Vladimiro Vinda, y en 1927 se creó la Comisión Geológica del Golfo San Jorge, a cargo del italiano Enrico FossaMancini. Se integró con un equipo de geólogos italianos, rusos y argentinos. Feruglio, Piatnitzky, Stessin, Serghiescu, Ramaccioni, Chahnazaroff, Franceschi, Tarragona, Conci, Brandmayr, Wellhoefer, Biondi, Casanova, etc, son algunos de los protagonista entre 1927 y 1930. El primer trabajo encarado por la Comisión fue ajustar la estructura del yacimiento a partir de la nivelación de las capas terciarias y generar un modelo estructural de entrampamiento. Siguiendo los lineamientos hacia el oeste se descubrieron los grandes yacimientos del Flanco Norte, como Cañadón Perdido, Diadema, Escalante, Manantiales Behr, El Trébol, Pampa del Castillo y El Tordillo. Paralelamente, se perforaron los anticlinales aflorantes en Pampa María Santísima, Codo del Senguer y Perales. A fines de la década del 30 se encaró la exploración profunda del Chubutiano en el flanco norte y se trasladó el modelo hacia el flanco sur descubriéndose Cañadón Seco, Cañadón León y Meseta Espinosa. El trabajo de los primeros geólogos de YPF tuvo un gran impacto en la incorporación de recursos energéticos y permitió contar con un completo panorama geológico de la Patagonia, dando origen a una escuela de trabajo en la que por décadas se formaron los profesionales de exploración del país.

Geophysical image of the hydrothermal system of Merapi volcano

We present an image of the hydrothermal system of Merapi volcano based on results from electrical resistivity tomography (ERT), self-potential, and CO2 flux mappings.The ERT models identify two distinct low-resistivity bodies interpreted as two parts of a probably interconnected hydrothermal system: at the base of the south flank and in the summit area. In the summit area, a sharp resistivity contrast at ancient crater rim Pasar-Bubar separates a conductive hydrothermal system (20–50Ωm) from the resistive andesite lava flows and pyroclastic deposits (2000–50,000Ωm). The existence of preferential fluid circulation along this ancient crater rim is also evidenced by self-potential data. The significative diffuse CO2 degassing (with a median value of 400gm−2d−1) is observed in a narrow vicinity of the active crater rim and close to the ancient rim of Pasar-Bubar. The total CO2 degassing across the accessible summital area with a surface of 1.4 ⋅ 105m2 is around 20td−1. Before the 2010 eruption, Toutain et al. (2009) estimated a higher value of the total diffuse degassing from the summit area (about 200–230td−1). This drop in the diffuse degassing from the summit area can be related to the decrease in the magmatic activity, to the change of the summit morphology, to the approximations used by Toutain et al. (2009), or, more likely, to a combination of these factors.On the south flank of Merapi, the resistivity model shows spectacular stratification. While surficial recent andesite lava flows are characterized by resistivity exceeding 100,000Ωm, resistivity as low as 10Ωm has been encountered at a depth of 200m at the base of the south flank and was interpreted as a presence of the hydrothermal system. No evidence of the hydrothermal system is found on the basis of the north flank at the same depth. This asymmetry might be caused by the asymmetry of the heat supply source of Merapi whose activity is moving south or/and to the asymmetry in topography caused by the presence of Merbabu volcano in the north. On the basis of our results we suggest that stratified pyroclastic deposits on the south flank of Merapi screen and separate the flow of hydrothermal fluids with the gaseous part rising through the crater rims, while the liquid part is flowing downwards to the base of the edifice.

The explosive activity of the 1669 Monti Rossi eruption at Mt. Etna (Italy)

Preceded by 14days of intense seismic activity, a new eruption started on the south flank of Mt. Etna, Sicily (Italy) early in the morning of 11 March 1669 opening up a series of NS eruptive fissures.The eruption is one of the most destructive flank eruptions of Etna in historical times; it lasted until 11 July, and was characterized by simultaneous explosive and effusive activity during the first three months, while only lava flow output in the last month. The activity built up the large composite cone of the “Monti Rossi” at the lower end of the eruptive fissures, and caused severe damage to the nearby inhabited areas. The prolonged effusive activity generated lava flows for >15km, which destroyed several villages and the western part of the town of Catania before reaching the coastline and entering the sea.In this paper, we examine the tephro-stratigraphy of the products of the explosive activity. An in-depth analysis of historical accounts was used to define the chronology of the main eruptive phases (precursors, explosive activity and initial effusive phenomena). The geology of the cone and of the fallout deposits were defined through a field survey over a distance of 5km from the Monti Rossi. Textural (grain-size, morphological, componentry), density and petrological analyses of tephra samples provided a sedimentological, physical and geochemical characterization of erupted products. Integrating ground and historical data enabled defining the evolution of the cone, identifying and correlating four main cone-forming units. By tracing the dispersal map of the main distal tephra beds (the finer ash being dispersed mainly to the NE as far as Calabria and to the south of Sicily and the 10-cm isopach of the total deposit covering an area up to 53km2), we estimated a total tephra fallout volume, including the Monti Rossi cone, of about 6.6×107m3 (about 3.2×107m3 DRE).The 1669 event can be considered an archetype of the most hazardous expected eruption on the densely populated flanks of Etna. Reconstructing the eruptive chronology and styles of the 1669 eruption therefore, represents the basic data to assess volcanic hazard from eventual similar flank events in the future.

Controls on channel width in an intermontane valley of the frontal zone of the northwestern Himalaya

Channel width is an important parameter of the hydraulic geometry of a river and can be linked to the tectonic, topographic, lithologic, and climatic controls in a particular reach. As such, variations in channel width can be the result of one or many factors acting at a specific location. For the rivers flowing in the intermontane valleys along the frontal Himalaya, active tectonics plays a major role in controlling their geometry by providing the space, energy, and sediment. Dehra Dun is an intermontane valley in the northwestern Himalaya where the rivers have their source in the Lesser Himalaya and Sub-Himalaya; they show remarkable variability in the channel width along their course. In this work, we have attempted to identify and evaluate the relative importance of various controlling factors on the channel width of these drainage systems. We selected 20 streams (six North Flank rivers - NFRs; two Main Axial rivers - MARs; twelve South Flank rivers - SFRs) flowing in the valley. In the hilly stretches, the NFRs flow over the Lesser Himalaya and the SFRs flow over the poorly consolidated upper Siwalik gravelly sediments. Channel width in the mountainous region varies generally from 5 to 30m. The SFRs that have smaller catchments are relatively wider than the NFRs in the mountainous areas. In the Dun, the width variation is mostly between 50 and 400m. The NFRs show widening in their middle stretches except for the Tons River, which is wide in its lower stretch. Channels widen as they cross the structural zones (i.e., the Main Boundary Thrust (MBT), the Santaurgarh Thrust (ST), and the Bhauwala Thrust (BT)) as a result of the change in the gradient across the structures. Large sediment supply generated by mass wasting processes from the weak zones (i.e., fault-related zones) and uplifted surfaces make the river transport limited, resulting in the deposition of the sediments. Consequently, channel bed armoring in these gravel-bed rivers protects the channel floor causing the erosive actions to be intensified on the banks. In the Dun, where the channel banks consist of cohesive materials, the bank erosion is found to be limited. Apart from these controls, anthropogenic interventions and activities also impact the channel width in the valley. The NFRs and MARs are embanked at many places. On the other hand, most of the SFRs become indistinct before the confluence with the larger rivers because of farming-related activities. This study suggests that in the mountainous stretches, the lithology and geologic structures exercise a primary control over the channel width; whereas within the Dun, the sediment concentration, channel bed armoring, and the properties of bank materials act as the main controls.

Depositional Setting and Structural Evolution of the Archean Perseverance Volcanogenic Massive Sulfide Deposit, Matagami Mining District, Quebec, Canada

The Perseverance volcanogenic massive sulfide deposit (5.1 Mt at @ 15.8% Zn, 1.24% Cu, 29.4 g/t Ag, 0.4 g/t Au), Matagami district, Abitibi greenstone belt, consists of four pipelike orebodies discordant to local bedding in a shallow-dipping portion of the South Flank volcanic succession. Most of the ore is hosted by rhyolitic lavas of the Watson unit (2725.9 ± 0.8 Ma) and is overlain by a thinly laminated tuffaceous unit known as the Key Tuffite, as well as by rhyodacitic lavas of the Dumagami unit (2725.4 ± 0.7 Ma). The presence of sulfide zones predominantly hosted in the footwall rhyolite, relicts of Key Tuffite within the ore, and intricate sulfide replacement of the laminated tuff are all features consistent with the formation of most of the deposit via subseafloor replacement. The permeability of steep synvolcanic structures likely controlled the migration of metal-bearing fluids and simultaneously allowed the downward infiltration of seawater, causing mixing, cooling, and sulfide deposition in the subseafloor environment. Stratigraphic relationships suggest that massive sulfide formation was active at Perseverance while tuffaceous sedimentation was ongoing on the seafloor. Progressive growth of the massive sulfides along subvertical structures was accompanied by the development of pipelike sericite-chlorite (± talc) alteration halos. Both the hanging wall and the footwall units are characterized by significant MgO mass gains, K 2 O-Na 2 O mass losses, and high alteration index values (e.g., chlorite-carbonate-pyrite index, alteration index). However, these geochemical changes are less intense and widespread in the hanging wall than in the footwall. The record of a decreasing alteration above the orebodies was likely caused by the emplacement of the rhyodacite while massive sulfide deposition and hydrothermal activity were still ongoing. Primary relationships between mineralization and the host lithofacies were overprinted by intense deformation during the main event of compression induced by regional north-south shortening. Deformation is controlled by contrasting rheologies within the sulfide assemblage and between the orebodies and their host rocks. Structural modifications include the transposition of sulfide ores subparallel to the main foliation, the formation of piercement veins at the interface with the host rocks, and the generation of a series of secondary textures within the orebodies, including a vertical mineralogical banding. The distribution of Cu in the deposit is interpreted to be affected by the mechanical remobilization of chalcopyrite during deformation, whereas the zonation of Zn is likely primary. Hydrothermal alteration halos adjacent to the orebodies have accommodated significant strain, as indicated by the presence of tight folds in the Key Tuffite unit and a marked schistosity. Strain localization in the vicinity of the deposit highlights the relative ductility of the ore assemblage with respect to the host volcanic succession and resulted in a spatial association between hydrothermal alteration and deformation, despite the lack of a genetic relationship.

Joint relative location of earthquakes without a pre-defined velocity model: an example from a peculiar seismic cluster on Katla volcano's south-flank (Iceland)

Relative location methods are commonly used to precisely locate earthquake clusters consisting of similar waveforms. Repeating waveforms are often recorded at volcanoes, where, however, the crust structure is expected to contain strong heterogeneities and therefore the 1-D velocity model assumption that is made in most location strategies is not likely to describe reality. A peculiar cluster of repeating low-frequency seismic events was recorded on the south flank of Katla volcano (Iceland) from 2011. As the hypocentres are located at the rim of the glacier, the seismicity may be due to volcanic or glacial processes. Information on the size and shape of the cluster may help constraining the source process. The extreme similarity of waveforms points to a very small spatial distribution of hypocentres. In order to extract meaningful information about size and shape of the cluster, we minimize uncertainty by optimizing the cross-correlation measurements and relative-location process. With a synthetic test we determine the best parameters for differential-time measurements and estimate their uncertainties, specifically for each waveform. We design a location strategy to work without a pre-defined velocity model, by formulating and inverting the problem to seek changes in both location and slowness, thus accounting for azimuth, take-off angles and velocity deviations from a 1-D model. We solve the inversion explicitly in order to propagate data errors through the calculation. With this approach we are able to resolve a source volume few tens of metres wide in horizontal directions and around 100 metres in depth. There is no suggestion that the hypocentres lie on a single fault plane and the depth distribution indicates that their source is unlikely to be related to glacial processes as the ice thickness is not expected to exceed few tens of metres in the source area. Our method is designed for a very small source region, allowing us to assume a constant slowness for the whole cluster and to include the effects of 3-D heterogeneity such as refraction. Similar circumstances may arise in other volcanic regions with a high level of heterogeneity and where densely clustered earthquakes are often recorded.

A large refined catalog of earthquake relocations and focal mechanisms for the Island of Hawai'i and its seismotectonic implications

AbstractWe present high‐quality focal mechanisms based on a refined earthquake location catalog for the Island of Hawai'i, focusing on Mauna Loa and Kīlauea volcanoes. The relocation catalog is based on first‐arrival times and waveform data of both compressional and shear waves for about 180,000 events on and near the Island of Hawai'i between 1986 and 2009 recorded by the seismic stations at the Hawaiian Volcano Observatory. We relocate all the earthquakes by applying ray tracing through an existing three‐dimensional velocity model, similar event cluster analysis, and a differential‐time relocation method. The resulting location catalog represents an expansion of previous relocation studies, covering a longer time period and consisting of more events with well‐constrained absolute locations. The focal mechanisms are obtained based on the compressional‐wave first‐motion polarities and compressional‐to‐shear wave amplitude ratios by applying the HASH program to the waveform cross correlation relocated earthquakes. Overall, the good‐quality (defined by the HASH parameters) focal solutions are dominated by normal faulting in our study area, especially in the active Ka'ōiki and Hīlea seismic zones. Kīlauea caldera is characterized by a mixture of approximately equal numbers of normal, strike‐slip, and reverse faults, whereas its south flank has slightly fewer strike‐slip events. Our relocation and focal mechanism results will be useful for mapping the seismic stress and strain fields and for understanding the seismic‐volcanic‐tectonic relationships within the magmatic systems.

Long-period seismic events with strikingly regular temporal patterns on Katla volcano's south flank (Iceland)

Katla is a threatening volcano in Iceland, partly covered by the Mýrdalsjökull ice cap. The volcano has a large caldera with several active geothermal areas. A peculiar cluster of long-period seismic events started on Katla's south flank in July 2011, during an unrest episode in the caldera that culminated in a glacier outburst. The seismic events were tightly clustered at shallow depth in the Gvendarfell area, 4km south of the caldera, under a small glacier stream at the southern margin of Mýrdalsjökull. No seismic events were known to have occurred in this area before. The most striking feature of this seismic cluster is its temporal pattern, characterized by regular intervals between repeating seismic events, modulated by a seasonal variation. Remarkable is also the stability of both the time and waveform features over a long time period, around 3.5years. We have not found any comparable examples in the literature. Both volcanic and glacial processes can produce similar waveforms and therefore have to be considered as potential seismic sources. Discerning between these two causes is critical for monitoring glacier-clad volcanoes and has been controversial at Katla. For this new seismic cluster on the south flank, we regard volcano-related processes as more likely than glacial ones for the following reasons: 1) the seismic activity started during an unrest episode involving sudden melting of the glacier and a jökulhlaup; 2) the glacier stream is small and stagnant; 3) the seismicity remains regular and stable for years; 4) there is no apparent correlation with short-term weather changes, such as rainstorms. We suggest that a small, shallow hydrothermal system was activated on Katla's south flank in 2011, either by a minor magmatic injection or by changes of permeability in a local crack system.

Interannual Shift of the Tropical Upper-Tropospheric Trough and Its Influence on Tropical Cyclone Formation over the Western North Pacific

AbstractThe east–west migration of the tropical upper-tropospheric trough (TUTT) on the interannual time scale and its influence on tropical cyclone (TC) formation over the western North Pacific (WNP) is investigated in this study. Climatologically, the TUTT can be identified from 100 to 400 hPa with a relative vorticity maximum between 150 and 200 hPa. In addition to the strong westerly vertical wind shear in the south flank of the TUTT, this study shows that the cold-core system is associated with low relative humidity and subsidence to the east of the trough axis. As a result, the TC formation is enhanced (suppressed) in the eastern portion of the WNP when the TUTT shifts eastward (westward) on the interannual time scale. The interannual TUTT shift is closely associated with the SST anomalies in the central and eastern tropical Pacific or ENSO phases. The warm (cold) phase of ENSO corresponds to the eastward (westward) shift of the TUTT. The physical factors found to be responsible for the influence of ENSO on TC formation can be associated with the east–west shift of the TUTT. It is shown that the interannual variations of TC formation in the eastern part of the WNP basin are closely associated with the east–west shift of the TUTT due to the associated environmental conditions that are generally not favorable for TC formation.

Unraveling multiple provenance areas using sandstone petrofacies and geochemistry: An example in the southern flank of the Golfo San Jorge Basin (Patagonia, Argentina)

The aim of this paper is to study the provenance of Late Cretaceous sandstones deposited along the south flank of the Golfo San Jorge Basin. For this purpose, detrital modes of three hundred thirty-seven sandstone samples collected in the Mina del Carmen, Bajo Barreal, and Cañadón Seco Formations were studied in ten oil fields. According to the modal composition of the sandstones, six petrofacies were defined allowing the identification of not only principal, but also secondary provenance areas. The QVM and VQM petrofacies are more than 20% metamorphic, sedimentary, and polycrystalline quartz clasts (Lm + Ls + Qpg > 20%), evidencing a secondary signal of basement supply masked by a predominant volcanic provenance. The petrofacies VP and VF are characterized by Lm + Ls + Qpg <20% and more than 20% total feldspar (Pm + Om >20%.), which indicate a supply of sediment from volcanic terrains and scarce derivation of materials from basement rocks. Based on the plagioclase/k-feldspar ratio, the VF petrofacies is interpreted to be dominated by the supply of sand grains from the Andean volcanic-arc, while VP is supposed have originated through the erosion of intermediate volcanic rock outcroppings in the Macizo del Deseado. Finally, both the VQ and QV petrofacies show Lm + Ls + Qpg <20% and Pm + Om<20%, indicating a provenance of volcanic areas coupled with minor contributions from basement rocks. During the Late Cretaceous, the Golfo San Jorge Basin underwent a sag phase that was characterized by very scarce volcanism and tectonic activity. Although these conditions did not favor defined patterns in the vertical stacking of petrofacies, the sandstones exhibit remarkable changes in their regional distribution, which were determined by the paleogeography of the basin and differences in basement composition within the source areas. Finally, a paleogeographic model for sediment circulation in the basin is proposed. This model recognizes the main fluvial dispersal trends that flowed northwest to southeast and transported large amounts of volcanic clasts (associated with petrofacies VF-VQ). To the extent that rivers flowed eastward, a secondary supply from the Precambrian basement, which were composed of low-to high-grade metamorphic rocks, was also important (petrofacies association VQM and QVM). The southwestern area of the basin is dominated by VP petrofacies that record the supply of plagioclase-rich volcanic clasts. This petrofacies likely corresponds to the erosion of Jurassic volcanic units that crop out in the Macizo del Deseado.

КРАХ БІПОЛЯРНОСТІ ТА НОВИЙ ГЕОСТРАТЕГІЧНИЙ СТАТУС РОСІЙСЬКОЇ ФЕДЕРАЦІЇ

The content of the new geo-strategic status of the Russian Federation that emerged after the collapse of the world socialist system and the collapse of the Soviet Union. The strategic conditions in which Russia is closely linked to the geopolitical environment that developed after the emergence of new independent states, the department new Russian borders. Russia in comparison with the USSR lost 25% of the territory, more than half of the population and the industrial and economic potential. RF is currently trying to stick to the geopolitical balance between Europe and Asia with a view to obtaining the role of the Eurasian transcontinental bridge. At the same time Russia was faced with geopolitical realities, which are connected with the restriction of its communications and foreign policy capabilities influence both on the west and south-east directions in connection with the new status of yesterday’s post-Soviet republics. Ukraine, Belarus and other former Soviet states of Eastern Europe addressed by the Russian Federation only as a geopolitical buffer on the south-western strategic flank. In the end, on the South Caucasus and Central Asia is assigned as a buffer on the south and south-east strategic flanks. From the point of view of the Russian geostrategy «vulnerable» segment of the border remains, which borders with Poland and the Baltic states. However, in recent years, Russia gradually loses its geopolitical influence in Ukraine, Georgia, Moldova. There is a significant probability that in the medium term, Belarus will pay its strategic vector of foreign policy towards the EU and NATO. Such transformation in the foreign policy of the newly independent states will be another step in the destruction of geopolitical influence of Russia in the post-Soviet space. This situation is further more than changing the geopolitical landscape of the post-Soviet space and affects the geopolitical picture of the world as a whole.