Semicircular Depressions Research Articles

Anti-planar response due to cylindrical cavity with linear crack under semicircular canyon

Surface depressions and subsurface defects have been a trendy topic in ground shaking problems. In the case of canyon tunnels and canyon pipeline projects, surface movement and cavity edge stress concentrations have been a concern in the design, and the effects of cracks need to be considered if the underground structure contains cracks. In this paper, the wave scattering problem in an elastic half-space medium containing semicircular depression(canyon), cylindrical cavity and crack is investigated by using theoretical methods, the wave function expansion method, the complex function method and the mirror image method to solve the control equation in the form of Helmholtz equation satisfying the zero-stress boundary condition, and the corresponding displacement function is solved. The Green function method and the crack “cutting” technique are used to construct cracks. The unknown coefficients in the system of equations to be determined are solved by free boundary conditions combined with Fourier expansion. The displacement field is a superposition of appropriate wave fields. Finally, the effects of the relevant parameters on ground motion |w| (w), dynamic stress intensity factor (DSIF) of the tip of crack and the dynamic stress concentration factor (DSCF)of the cylindrical cavity were investigated by frequency and time domain analysis. This study not only provides a theoretical basis for practical unlined tunnels or pipeline projects, but also provides a basis for the seismic design of underground structures.

Fuzzy response to SH guided-wave scattering by semicircular depressions on the boundary of a ribbon-shaped elastic plate

In this paper, the fuzzy scattering problem with semicircular depressions on the boundary of a band-shaped elastic plate with steady SH guided wave incident is studied and an analytical solution is given. First, the SH guided wave is constructed by the guided wave expansion method, and then the scattered wave satisfying the free condition of the boundary stress of the strip domain is constructed by the cumulative mirror method. Finally, a definite solution equation is obtained based on the fact that the shear stress at the edge of the semi-circular recessed hole is zero. In this paper, the ambiguity of the number of waves and the width of the bands is taken into account. In order to avoid the irreversibility of interval algorithm and the difficulty of solving non-linear equations, the membership function of fuzzy quantity is segmented to make the membership degree and fuzzy quantity correspond respectively. A deterministic problem that translates into piecewise processing. Two numerical examples are given to examine the changes in fuzzy response of different numbers of fuzzy waves and fuzzy thicknesses to the dynamic stress concentration factor of the hoop at the collapse limit.

Ground motion around a semi-cylindrical canyon in saturated soil: P wave incidence

Based on Biot wave theory in saturated two-phase medium, the analytical solution of plane P-wave scattering by semi-circular canyon in half space in saturated two-phase medium is given by using complex function method and Hankel function integral transformation method. Firstly, a semi-circular depression model in saturated half space is constructed, the wave field potential function in the medium is solved, and its general solution form is obtained. Secondly, the unknown coefficient value in the potential function is obtained by substituting the corresponding stress boundary conditions. With the help of Hankel function integral transformation method, the wave potential function in complex coordinates is transformed to meet the horizontal boundary conditions of half space in rectangular coordinates. Finally, the surface displacement amplitude at the semi-circular depression and the surrounding horizontal boundary is obtained through the total wave field potential function, and the variation law of surface displacement amplitude under the influence of different parameters is analyzed.

Seismic characterization and depositional significance of the Nahr Menashe deposits: Implications for the terminal phases of the Messinian salinity crisis in the north‐east Levant Basin, offshore Lebanon

AbstractOver the last decade, there has been a resurgence of interest in the climatic and tectonic mechanisms that drove the Messinian salinity crisis (MSC) and the associated deposition of thick evaporites. The MSC represents an unprecedented palaeoceanographic change that led to a very short (ca. 640 kyr) ecological and environmental crisis. However, across the Levantine offshore basin, the sedimentological nature of the top evaporitic units and the mechanisms that controlled the transition from a hypersaline evaporitic unit to brackish deposits (final MSC stage 3) are still disputed. Here, we re‐evaluate the deposits associated with the terminal phase of the MSC, named in offshore Lebanon as the Nahr Menashe Unit (NMU). We describe the NMU seismic facies, characterize and map its internal seismic stratigraphy and provide a new interpretation of its depositional environment, which persisted during the late Messinian and then evolved through a regional reflooding event. The base of the NMU overlies semicircular depressions, randomly distributed linear marks and surface collapse features, which are indicative of a period of intense evaporite dissolution. The NMU seismic facies observed from the slope to the deep part of the basin support the interpretation of a layered salt‐evaporite‐sand depositional system subject to complex reworking, dissolution, deposition and final erosion. A drainage network of valleys and complex tributary channels incising into the top NMU shows marked erosional characteristics, which indicate a dominant southwards sediment transfer following deposition of the NMU. The drainage network was subsequently infilled by layered sediments interpreted here to represent the post‐MSC marine sediments. Our analysis adds important details regarding previous interpretations of the NMU as fluvial in origin. Specifically, the presence of subcircular, linear dissolution features coupled with mound‐like features indicates that the NMU is composed dominantly of evaporites that were subject to dissolution prior to erosion associated with the drainage network. The NMU is interpreted to represent the deposition/redeposition of a mixed evaporite‐siliciclastic succession in a shallow marine or lacustrine environment during the tilting of the offshore Lebanese basin.

Two new species of the subgenus Pleurosticha of the genus Chrysolina (Coleoptera: Chrysomelidae) from the mountains of southern Siberia (Altai and Tyva)

Two new species from the subgenus Pleurosticha of the genus Chrysolina are described from the mountains of southern Siberia (Russia): Ch. reshetnikovi sp. nov. (Republic of Altai) and Ch. borisi sp. nov. (Republic of Tyva). Chrysolina reshetnikovi sp. nov. has a slightly convex body, a blue-green coloration of the upper side, regular puncture rows of the elytra and mostly flat elytral intervals, which distinguish this species from all species of the subgenus, except for Ch. shapkini Mikhailov et Gus’kova, 2013. The main distinguishing features of the male of the new species from Ch. shapkini are the strongly broadened tarsomeres 1–3, the pygidium with an impression along its entire length, the last abdominal sternite with a semicircular depression, and the apex of the aedeagus bent at 90°. Chrysolina borisi sp. nov. has a convex small body, black coloration of the upper side, femora and tibiae, regular puncture rows of the elytra and slightly convex elytral intervals, and the aedeagus near the apex with a narrow protrusion of the lateral side directed toward the aedeagus base.

Dynamic response of a half-space with a depression covered by viscous liquid under SH waves

This study examines the problem of the displacement amplitude at the interface of an elastic half-space with a semicircular depression covered by a viscous liquid under the action of shear horizontal (SH) waves. First, the half-space incident wave field is constructed. Simultaneously, the scattering displacement field of the problem is obtained using the large circle and complex variable function methods. Thereafter, based on the boundary conditions at the fluid-solid interface, an infinite linear algebraic equation is established to obtain the unknown coefficients of the wave function. Finally, the changes in the interface displacement amplitude caused by SH wave scattering are obtained. Numerical examples reveal that the thickness, dynamic viscous coefficient, density of the viscous liquid, and incident wave frequency all affect the displacement amplitude at the interface. This paper also presents valuable conclusions that are expected to help guide the study of engineering structures with recessed half-spaces covered by viscous liquids.

Semi-circular Depression on the Leg Diagnosed by High-frequency Ultrasound: A Quiz.

Semi-circular Depression on the Leg Diagnosed by High-frequency Ultrasound: A Quiz.

Surface Motion of a Half-Space Containing an Elliptical-Arc Canyon under Incident SH Waves

The existence of local terrain has a great influence on the scattering and diffraction of seismic waves. The wave function expansion method is a commonly used method for studying terrain effects, because it can reveal the physical process of wave scattering and verify the accuracy of numerical methods. An exact, analytical solution of two-dimensional scattering of plane SH (shear-horizontal) waves by an elliptical-arc canyon on the surface of the elastic half-space is proposed by using the wave function expansion method. The problem of transforming wave functions in multi-ellipse coordinate systems was solved by using the extra-domain Mathieu function addition theorem, and the steady-state solution of the SH wave scattering problem of elliptical-arc depression terrain was reduced to the solution of simple infinite algebra equations. The numerical results of the solution are obtained by truncating the infinite equation. The accuracy of the proposed solution is verified by comparing the results obtained when the elliptical arc-shaped depression is degraded into a semi-ellipsoidal depression or even a semi-circular depression with previous results. Complicated effects of the canyon depth-to-span ratio, elliptical axis ratio, and incident angle on ground motion are shown by the numerical results for typical cases.

Potential links between Baltic Sea submarine terraces and groundwater seeping

Abstract. Submarine groundwater discharge (SGD) influences ocean chemistry, circulation, and the spreading of nutrients and pollutants; it also shapes sea floor morphology. In the Baltic Sea, SGD was linked to the development of terraces and semicircular depressions mapped in an area of the southern Stockholm archipelago, Sweden, in the 1990s. We mapped additional parts of the Stockholm archipelago, areas in Blekinge, southern Sweden, and southern Finland using high-resolution multibeam sonars and sub-bottom profilers to investigate if the sea floor morphological features discovered in the 1990s are widespread and to further address the hypothesis linking their formation to SGD. Sediment coring and sea floor photography conducted with a remotely operated vehicle (ROV) and divers add additional information to the geophysical mapping results. We find that terraces, with general bathymetric expressions of about 1 m and lateral extents of sometimes >100 m, are widespread in the surveyed areas of the Baltic Sea and are consistently formed in glacial clay. Semicircular depressions, however, are only found in a limited part of a surveyed area east of the island of Askö, southern Stockholm archipelago. While submarine terraces can be produced by several processes, we interpret our results to be in support of the basic hypothesis of terrace formation initially proposed in the 1990s; i.e. groundwater flows through siltier, more permeable layers in glacial clay to discharge at the sea floor, leading to the formation of a sharp terrace when the clay layers above seepage zones are undermined enough to collapse. By linking the terraces to a specific geologic setting, our study further refines the formation hypothesis and thereby forms the foundation for a future assessment of SGD in the Baltic Sea that may use marine geological mapping as a starting point. We propose that SGD through the submarine sea floor terraces is plausible and could be intermittent and linked to periods of higher groundwater levels, implying that to quantify the contribution of freshwater to the Baltic Sea through this potential mechanism, more complex hydrogeological studies are required.

Genesis and Morphotectonic Characterisation of Crescent- Shaped feature from Alcock Rise, Andaman Sea

Study of 98 crescent shape depressions over Alcock Rise, Andaman Sea were reported for the first time in between water depth -500 and -2000 m using multibeam swath bathymetry data. These gigantic depressions have crescent length (CL) varies from 600 to 3800 m and width (CW) varies from 200 to 2500 m with an average central depression of 500 m. Detailed parametric characterization reveals that slope and axial ratio of these crescentic structures have no direct relationship with general shape and steepness of their escarpment. Moreover, spatial distribution of these structures show a clustering of elongated crescent with higher crescent length to width ratio in NW margin of Alcock Rise compare to centre. This change in shape from open elliptical to semicircular depression probably suggests that earlier formed open crescents were modified at later stage to semicircular depressions. As observed in the seismic data, the formation of the crescentic depressions were initiated by the normal fault in-association with major dextral transform fault and subsequently its geometry was modified by local transpression along with seismicity induced slumping and bottom current scouring from the weaker zones. So, tectonics and bottom current activity provides simpler explanation for the formation of crescentic structure over Alcock Rise.Keywords: Crescentic depression, Alcock Rise, Swath bathymetry, Bottom current, Normal fault.

Scattering of SH guided wave by a circular inclusion and semicircular depression in an infinite piezoelectric material strip

ABSTRACT By means of the guided wave theory, the scattering of SH guided wave by a circular inclusion and semicircular depression in an infinite piezoelectric material strip is investigated. The multi-polar coordinate change method is used to deal with semicircular sag at the boundary position. By using the method of multiple images, the theoretical expressions of scattering waves, satisfying the stress-free and electrical insulation conditions at the upper and lower boundaries of the band domain, are constructed. Based on the boundary conditions, the integral equations are established. The analytical expressions of the dynamic stress concentration coefficient and electric field intensity concentration coefficient are obtained. By analyzing the order of the guided wave, the physical parameters of the medium, the distance between the center of a circular inclusion, the location of a semicircular depression and a circular inclusion and the radius of the semicircular depression, the dynamic stress concentration factor and electric field intensity concentration factor are analyzed and compared with the existing literature in calculating example.

El Escondido, a newly identified silicic Quaternary volcano in the NE region of the northern volcanic segment (Central Cordillera of Colombia)

El Escondido (1650m.a.s.l.) is a silicic Quaternary volcano recently identified on the Central Cordillera of Colombian Andes. It is located about 50km NE from the northern segment of active volcanoes. It has been recognized as a polygenetic pyroclastic-dome ring complex structure, whose eruptive products derived from a crater-like semi-circular depression of ~1.7km in diameter. This crater formed at the contact of the Granitic Florencia Stock (54.9±1.8my) with the Paleozoic metamorphic basement, and at the intersection of the NNESSW trending Palestina fault system with an EW trending fault. The preserved volcano morphology and the volcanic succession associated with it were defined as the El Escondido volcanic center. The eruptive products are alternating silicic (mostly dacitic) pyroclastic density current deposits, pumice fall deposits and ballistic projectiles, which suggest high explosiveness. Two 14C radiogenic dates obtained on carbonized wood fragments of the middle part of the eruptive sequence displayed ages of 36,030±380 BP and 33,550±280 BP suggesting two major eruptive episodes of the volcano about 2500years apart. The latest eruptive activity is inferred to be the emplacement of lava domes to the south of the crater-like structure, which are responsible for the partial destruction of the pyroclastic ring in that sector. The products emitted by El Escondido correspond to medium K andesites to dacites of the calc-alkaline series and petrographically to amphibolic andesites. Towards the western and eastern sector of the volcano, there are chlorinated thermal waters with temperatures up to 45°C. The first monitoring of the volcanic activity, carried out by the Colombian Geological Survey (CGS) through the Volcanological and Seismological Observatory of Manizales (VSOM), has not detected so far unusual volcano-seismic activity. The previously unreported El Escondido volcano represents one of the northernmost occurrence of Quaternary volcanism in the whole Andean cordillera, thus, its study may have wide implications regarding the geodynamics of the region and subduction zone, the correct assessment of geologic hazards and the identification of natural resources, like geothermal reservoirs and mineral deposits of economic interest.

FROM EGGS TO HATCHLINGS: NEST SITE TAPHONOMY OF AMERICAN CROCODILE ( CROCODYLUS ACUTUS ) AND BROAD-SNOUTED CAIMAN ( CAIMAN LATIROSTRIS )

Abstract: Nesting behaviors of extant vertebrates can serve as taphonomic models for interpreting extinct archosaurian reproduction. Past studies have examined birds with open nests and nest-bound young and tortoises with buried nests and precocial young. Here we taphonomically describe nesting sites of two crocodylians, American crocodile (Crocodylus acutus) at Turkey Point, Florida and broad-snouted caiman (Caiman latirostris) from Santa Fe and Chaco provinces, Argentina. Surveys focused on eggshell abundance, orientation, and distribution and nest modification of successfully hatched nests. American crocodiles excavate triangular or semi-circular depressions into their nest during hatching. Maximum depths of these parent-assisted hatching traces ranged from 20–45 cm, with a breadth of 50–80 cm. Eggshell orientations outside these excavated pits favored concave down (53.1–80.0%). Broad-snouted caiman constructed mound nests of predominantly plant debris in forested areas with organic rich soil or on veg...

Seafloor terraces and semi-circular depressions related to fluid discharge in Stockholm Archipelago, Baltic Sea

Terraces and semi-circular depressions in the seafloor along islands in the southern Stockholm Archipelago, Sweden, were mapped in the 1990s with single-beam echo sounder and side-scan sonar equipment (Soderberg & Floden 1991, 1995). After inspection by divers, these features were interpreted to be formed by processes related to groundwater that disharged at the seafloor after flowing through permeable layers in glacial clay (Soderberg & Floden 1991, 1995). Erosional features related to submarine groundwater discharge (or sapping/piping) in the seafloor have been identified in many places and at a number of scales. For example, terraced walls and irregular courses of valleys in the continental slope of New Jersey are interpreted to be formed by groundwater sapping during periods of lower sea level (Robb 1984). The contribution of fresh groundwater to the sea is identified as an important component of the global hydrological cycle (Church 1996; Post et al. 2013) and also may contribute as much as 6–7% of the total freshwater discharge to the World Ocean (Zekster 2000 …

Lipoatrofia semicircular inducida por presión

Lipoatrophia semicircularis of the thighs is an uncommon form of localized lipodystrophy characterized by horizontal semicircular depressions distributed to form a band. The asymptomatic, often bilateral, and symmetric lesions are localized on the anterolateral aspect of the thighs. The pathogenesis of these lesions is unknown, although most cases are associated with repetitive trauma. A new hypothesis has implicated electromagnetic fields produced by computers and their cables in modern buildings as a cause. We describe a case in a 28-year-old woman of lipoatrophia semicircularis that was related to wearing tight pants.

Pressure-Induced Lipoatrophia Semicircularis

Lipoatrophia semicircularis of the thighs is an uncommon form of localized lipodystrophy characterized by horizontal semicircular depressions distributed to form a band. The asymptomatic, often bilateral, and symmetric lesions are localized on the anterolateral aspect of the thighs. The pathogenesis of these lesions is unknown, although most cases are associated with repetitive trauma. A new hypothesis has implicated electromagnetic fields produced by computers and their cables in modern buildings as a cause. We describe a case in a 28-year-old woman of lipoatrophia semicircularis that was related to wearing tight pants.

Lipoatrophia semicircularis: A compressive lipoatrophy consecutive to persistent mechanical pressure

Lipoatrophia semicircularis is an infrequent condition characterized by semicircular depressions of the anterolateral aspects of the thighs. The origin of this peculiar variant of lipoatrophy is unknown, although repeated mechanical trauma on the affected thighs has been advocated in many cases. A 57-year-old woman presented with a 1-year history of two bilateral, parallel, symmetric, asymptomatic depressions on the anterolateral aspect of her thighs. The patient worked as a cashier, permanently seated and almost always wearing trousers. The localization of lesions and their linear artifactual appearance perfectly matched with the strangling folds formed by trousers while being sat. Echotomographic examination revealed a loss of the normal echogenic pattern in the subcutaneous tissue of the affected areas. We believe that the anatomical adipose constitution of women's thighs predisposes that a persistent mechanical pressure induced by wearing trousers while being sat for long periods of time, originates a relative impaired circulation on a tenuous perfused tissue, and induces the development of lipoatrophia semicircularis.

Effect of surfactants on film flow down a periodic wall

The effect of an insoluble surfactant on the gravity-driven flow of a liquid film down an inclined wall with periodic undulations or indentations is investigated in the limit of vanishing Reynolds number. A perturbation analysis for walls with small-amplitude sinusoidal corrugations reveals that the surfactant amplifies the deformation of the film surface, though it also renders the film thickness more uniform over the inclined surface. The effect of the surfactant is most significant when the film thickness is less than half the wall period. To explain the deforming influence of the surfactant, a linear stability analysis of film flow down an inclined plane is undertaken for two-dimensional perturbations. The results reveal the occurrence of a Marangoni normal mode whose rate of decay is lower than that of the single mode occurring in the absence of surfactants. Numerical methods based on a combined boundary-element/finite-volume method are implemented to compute flow down a periodic wall with large-amplitude corrugations or semi-circular depressions. In the case of a wavy wall, it is found that the shape of the film surface is described well by the linear perturbation expansion for small and moderate wave amplitudes. Streamline patterns reveal that, although the effect of the surfactant on the shape of the film surface is generally small, Marangoni tractions may have a profound influence on the kinematics by causing the onset of regions of recirculating flow.

Structural and petrologic evolution of the Lihue basin and eastern Kauai, Hawaii

The topography of the eastern part of the Hawaiian island of Kauai is dominated by the Lihue basin, a large (∼110 km 2 ) semicircular depression bounded by steep cliffs and partly filled by late rejuvenated-stage (or posterosional stage) volcanic material. As with other large, semicircular basins on ocean-island volcanoes, the subsurface geology and origin (e.g., structural collapse vs. fluvial erosion) of the Lihue basin are poorly understood. New analyses of samples collected from eastern Kauai and drill holes within the basin document several important features of the late-stage geologic evolution of Kauai. First, thick (>300 m) sequences of rejuvenated-stage Koloa Volcanics in the Lihue basin show systematic, basin-wide geochemical trends of increasingly incompatible elements with time, indicating a gradual decrease in the extent of partial melting of mantle sources with time. Second, beneath the rejuvenated-stage volcanics in the basin, a thin layer of postshield alkalic stage lavas (e.g., hawaiites and mugearites) overlies older shield-stage tholeiitic lavas of the Napali Member, indicating that the Lihue basin formed by structural collapse, not fluvial erosion. Third, a large (∼2–5 km 3 ) matrix-supported breccia, interpreted as deposits of one or more debris flows, is within the rejuvenated-stage volcanics throughout the basin, and correlates with surficial exposures of the Palikea Breccia west of the basin. Isotopic compositions of the bulk breccia are similar to those of tholeiites from the east side of Kauai, and distinct from those of west Kauai tholeiites. Clasts within the breccia are dominantly hawaiite and alkali gabbro. The source region of the breccia in the steep cliffs and highlands of the central massif to the west of the basin must contain magmatic products of an extensive postshield alkalic stage, including hawaiite flows and one or more large intrusive bodies or ponded sequences of alkali gabbro.

浅間山天明噴火時の鎌原火砕流から泥流に変化した土砂移動の実態

A disastrous eruption of Asama volcano, the Tenmei eruption, occurred in 1783. During the eruption, “Kanbara pyroclastic flow” buried Kanbara Village located on the northern flank of the volcano, gradually changing into mudflow facies in the downstream. Furthermore, the mudflow went down along the Agatsuma and Tone Rivers. More than 1400 people were killed by this disaster. The pyroclastic flow is distributed within a parabolic area, with a narrow angle of 30deg; from a semi-circular depression with a diameter of 700 meters, which was located 4 km north of the summit. Aerial photo interpretation and field survey revealed that many gigantic blocks of essential lithics were scattered in an area of 18.1km2, and the volume of essentials was estimated to be 1.94×106 m3 for blocks with diameter upper 5m and 4.30×106m3 for including blocks with diameter lower 5m. The largest block was 49 meters in diameter, 10 meters high, and 9200 m3 in volume. Testpit survey clarified that the Kanbara pyroclastic flow deposit was 2.2 meters thick in average and hence amounted 4.70×107 m3 in total volume. Paleomagnetic measurement of the essential lithic blocks indicated that they deposited at a temperature higher than the Curie point (about 400deg;) even in the downstream of 65km from the summit. The pipe-structure observed in the several testpits was attributed to upward steam segregation, which derived from sufficient water and incandescent essential lithic blocks in the deposit.Considering historic pictures and documents which suggest the water overflowing during the eruption, the authors interpreted that the semi-circular depression was a swamp, “Yanai marsh”, of 1.0-2.5×107 m3 in capacity.The downflowing of Kanbara pyroclastic flow at high velocity caused an extensive erosion in the north slope of the volcano, because of much water content. The volume of the flow gradually increased since the deposit captured accidental blocks and water along the eroded area.We propose two alternative interpretations as follows:(1) The eruption occurred at the summit of Asama volcano and the pyroclastic flow rushed into the Yanai marsh, incorporating the water of the marsh into the flow. Consequently the Kanbara pyroclastic flow gradually changed into mudflow facies.(2) Lateral eruption occurred at the depression (the Yanai marsh) which had been filled with water.The pyroclastic materials successively mixed with the water, which flowed out of the depression, and changed into mudflow facies.