scholarly journals SEISMICITY of BAIKAL and TRANSBAIKALIA in 2015

2021 ◽  
pp. 129-138
Author(s):  
V. Melnikova ◽  
N. Gileva ◽  
A. Filippova ◽  
Ya. Radziminovich ◽  
E. Kobeleva
Keyword(s):  
Focal Mechanisms ◽  
P Wave ◽  
Normal Faults ◽  
Seismic Events ◽  
Study Region ◽  
Moment Tensors ◽  
North East ◽  
The North ◽  
First Arrival ◽  
Surface Wave Data

We consider the character of the seismic process in the Baikal and Transbaikalia regions in 2015. 36430 earthquakes with KR≥3 were recorded by seismic stations of permanent and temporary networks during the year due to the sharp increase of a number of seismic events at the north-east of the study region in the area of the large Muyakan seismic activation. 53 earthquakes were felt in the cities, towns and local settlements with an intensity not exceeding 6. The largest Tallaysk earthquake (KR=14.0, Mw=5.1) occurred at the North-Muya Ridge and was followed by few aftershocks. Focal mechanisms were determined for 118 seismic events from P-wave first-arrival polarities and based on seismic moment tensors inverted from the surface wave data. It has been found, that normal faults are realized in the sources of 49 % of earthquakes with the obtained focal mechanisms.

The shape and infill of the Basadingen overdeepened glacial valley from P-wave seismic reflections

2021 ◽  
Author(s):  
Anna-Catharina Brandt ◽  
David C. Tanner ◽  
Hermann Buness ◽  
Thomas Burschil ◽  
Gerald Gabriel
Keyword(s):  
P Wave ◽  
Borehole Data ◽  
North East ◽  
The North ◽  
Glacier Valley ◽  
Sedimentary System ◽  
Climatic History ◽  
The Alps ◽  
Seismic Reflections ◽  
Seismic Images

<p><span>Overdeepened valleys in the Alps allow to probe the glacial sedimentation record, which in turn can illuminate the climatic history. In particular, seismic reflections can be used to extend punctual borehole data (for instance a number of boreholes are to be drilled into Alpine glacial overdeepened valleys as part of the DOVE ICDP project) in the second dimension or even survey a region before drilling begins. Thus, we use detailed, 2-D seismic P-wave profiles to reveal the shape and infill of an overdeepened Rhine glacier valley in the area of Basadingen, near to the German/Swiss border. We acquired two profiles nearly perpendicular to the valley strike, approximately 500 m apart. The first profile was 1246 m long, and consisted of a single spread of 624 geophones. The second profile was 1120 m long and was acquired using 200 3-component geophones using a roll-along method. For both profiles we used a vibro-source with a 12 s linear sweep of 20-240 Hz at every second geophone (two metre spacing), which produced a high fold.</span></p><p><span>Both seismic images reveal that the overdeepened basin at this location is asymmetrical and circa 260 m deep, although the deepest part (220</span><span> </span><span>m wide) covers only a small portion of the broader main valley. The infill is characterised by at least three unconformities and distinct onlap and erosive boundaries between the sedimentary units. We interpret the infill to represent a highly dynamic sedimentary system. The lower part, within the deepest part of the basin is filled with chaotic sediments and slumping. Above a major unconformity, the upper part contains strongly-dipping reflectors that probably represent a prograding point-bar in a glacio-fluviatile environment that migrated toward the north-east. Beneath the deepest part of the basin we see evidence for faults in the Tertiary Molasse basement, which correlate with known faults at the surface. The faults most likely caused the valley to be sited at this location and they were probably also the cause of the ‘valley in valley’ shape.</span></p><p><span>A new DOVE research borehole will be drilled in the centre of the valley in 2021. This will bring more light on the sedimentary history and OSL-dating of the material will bracket the timing of the infill. </span></p>

Seismic deformation in the Western Alps : new insights from high resolution seismotectonic analysis

2020 ◽  
Author(s):  
Marguerite Mathey ◽  
Christian Sue ◽  
Bertrand Potin ◽  
Colin Pagani ◽  
Thomas Bodin ◽  
...  
Keyword(s):  
Interpolation Method ◽  
Western Alps ◽  
Focal Mechanisms ◽  
P Wave ◽  
Normal Faults ◽  
Stress And Strain ◽  
Strain Fields ◽  
3D Velocity Model ◽  
Moderate Seismicity ◽  
Seismic Deformation

<p>In the Western Alpine arc, GNSS measurements indicate that the far field convergence responsible for the Oligo-Miocene continental collision is now over. However, seismicity and slow deformation are still active. Former collisional tectonic features, such as the Penninic Front, are nowadays reactivated as normal faults. Indeed, geodetic and seismotectonic studies show that the inner part of the chain is undergoing transtensional deformation, although local compression is observed in the foothills at the periphery of the arc. Due to the low to moderate seismicity of the Western Alps, the stress and strain fields remain partly elusive.</p><p>The aim of the present study is to quantitatively assess the current seismic stress and strain fields within the Western Alps, from a probabilistic standpoint. We used a new set of more than 30,000 Alpine earthquakes recorded by the dense local Sismalp seismic network since 1989. We first computed well-constrained focal mechanisms (f.m.) for more than 2,000 events with Ml ranging from 0.5 to 4.9 based on first motion (P-wave) polarity. This is the first time that such a huge focal mechanism dataset can be analyzed in the Alps. Corresponding events have been localized using a 3D velocity model (B. Potin, 2016). The global distribution of P and T axes dips confirms a vast majority of dextral transtensive focal mechanisms in the overall Alpine realm. We interpolated these results based on a Bayesian interpolation method, providing a probabilistic 2D map of the styles of seismic deformation in the Western Alps. Compression is robustly retrieved only in the Pô plain where seismicity depth differs from the shallow seismicity of the Western Alps. Extension is localized at the center of the belt. Importantly, extension is clustered instead of continuous along the belt. We then summed seismic moment tensors in homogeneous volumes of crust, to obtain seismic strain rates directly comparable to geodetic ones. Last, we inverted f.m. together in specific areas to obtain principal stress directions. A major outcome is the orientation of the extension, which is surprisingly oblique to the arc, rather than normal, as commonly thought.</p><p>These results bring new insights on the geodynamic processes driving the seismotectonic activity of the Western Alps, such as the relative contributions of crustal tectonics and deep processes.</p>

scholarly journals Project Tor: Deep lithospheric variation across the Sorgenfrei-Tornquist Zone, Southern Scandinavia

1999 ◽  
Vol 46 ◽  
pp. 13-24
Author(s):  
Trine Pedersen ◽  
Søren Gregersen
Keyword(s):  
Upper Mantle ◽  
Surface Expression ◽  
P Wave ◽  
Northern Germany ◽  
Rectangular Array ◽  
Teleseismic Tomography ◽  
North East ◽  
The North ◽  
P Wave Velocity ◽  
Southern Scandinavia

The Tor project makes use of teleseismic tomography across the Sorgenfrei-Tornquist Zone and has now revealed significant variations in the deep lithosphere under northern Germany, Denmark and southern Sweden. Here we present the first interpretations of P-wave traveltime anomalies from the Tor project. The project utilised 120 seismographs placed in a rectangular array, the largest seismic antenna so far used in Europe, for half a year in the period 1996–1997. The present investigation establishes a 3D crustal/upper mantle model of the P-wave velocity based on existing data. A picture of the crustal influence on the seismic P-wave rays is established by ray tracing through the model. When this is subtracted from that observed by the Tor array, a picture of the influence of the lower lithosphere/asthenosphere system emerges. For several earthquakes it is shown that the observed P-wave traveltime anomalies of nearly 2 seconds can be divided almost equally between known crustal effects and lower lithosphere/asthenosphere differences. The transition appears gradual from most directions but for rays coming from the north-east direction the transition appears sharper. This means that the broad scale deep lithosphere transition is gradual with the sharpest discontinuity plane dipping down steeply in a north-easterly direction from the Sorgenfrei-Tornquist Zone. Based on existing knowledge of the area we conclude that the transition from thin to thick lithosphere occurs within a short distance, and that the lithosphere/asthenosphere boundary dips steeply down from the surface expression of the Sorgenfrei-Tornquist Zone.

scholarly journals Mapping of S4 Over the Arabian Peninsula During Solar Minimum

2021 ◽  
Author(s):  
Abdollah Darya ◽  
Muhammad Shaikh ◽  
Ilias Fernini ◽  
Hamid AlNaimiy
Keyword(s):  
Solar Minimum ◽  
Arabian Peninsula ◽  
Ionospheric Irregularities ◽  
Scintillation Index ◽  
Study Region ◽  
Amplitude Scintillation ◽  
North East ◽  
The North ◽  
Western Side ◽  
Using Data

In this letter, we study the temporal and spatial variability of ionospheric irregularities by generating high-resolution maps of the observed amplitude scintillation index (S4) using data from a multi-constellation and multi-frequency GNSS receiver. The study region is the Arabian Peninsula, which falls under the northern crest of the equatorial ionization anomaly (EIA). Even though the study was conducted during a solar minimum period, considerable occurrences of pre-sunset scintillation have been observed between 15-17 local time, particularly during the winter solstices. While most scintillation occurrences have been observed at low elevation (15 to 30 degrees), a considerable number of scintillation patches have been observed towards the north, east, and southeast of the receiver location, for elevation angles ranging from 40 to 60 degrees. Our analysis shows that BeiDou geostationary orbit (GEO) and inclined GEO (IGSO) satellites may have been the main contributor to the increased number of scintillation occurrences observed around the eastern side of the receiver as compared to the western side. Out of all the GNSS constellations with MEO satellites, GPS was the most impacted by amplitude scintillation, while BeiDou and Galileo satellites were the least affected. It is anticipated that the patches of ionospheric irregularities reported in this work would be further enhanced as the solar activity increases in the coming years. Therefore, this work can serve as a reference for future studies during periods of increased geomagnetic activity.

scholarly journals Descriptive text to the Geological map of Greenland, 1:100 000, Kilen 81 Ø.1 Syd

2018 ◽  
pp. 1-29
Author(s):  
Kristian Svennevig ◽  
Peter Alsen ◽  
Pierpaolo Guarnieri ◽  
Jussi Hovikoski ◽  
Bodil Wesenberg Lauridsen ◽  
...  
Keyword(s):  
Hanging Wall ◽  
Field Work ◽  
Normal Faults ◽  
The South ◽  
Thrust Sheet ◽  
Basin Inversion ◽  
North East ◽  
The North ◽  
Geological Map ◽  
Surrounding Areas

The geological map sheet of Kilen in 1:100 000 scale covers the south-eastern part of the Carboniferous– Palaeogene Wandel Sea Basin in eastern North Greenland. The map area is dominated by the Flade Isblink ice cap, which separates several minor isolated landmasses. On the semi-nunatak of Kilen, the map is mainly based on oblique photogrammetry and stratigraphical field work while in Erik S. Henius Land, Nordostrundingen and northern Amdrup Land the map is based on field data collected during previous, 1:500 000 scale regional mapping. Twenty-one Palaeozoic–Mesozoic mappable units were identified on Kilen, while the surrounding areas comprise the Late Cretaceous Nakkehoved Formation to the north-east and the Late Carboniferous Foldedal Formation to the south-west. On Kilen, the description of Jurassic–Cretaceous units follows a recently published lithostratigraphy. The Upper Palaeozoic–lowermost Cretaceous strata comprise seven formations and an informal mélange unit. The overlying Lower–Upper Cretaceous succession comprises the Galadriel Fjeld and Sølverbæk Formations, which are subdivided into six and five units, respectively. In addition, the Quaternary Ymer Formation was mapped on south-east Kilen. The Upper Palaeozoic to Mesozoic strata of Kilen are faulted and folded. Several post-Coniacian NNW–SSE-trending normal faults are identified and found to be passively folded by a later N–S compressional event. A prominent subhorizontal fault, the Central Detachment, separates two thrust sheets, the Kilen Thrust Sheet in the footwall and the Hondal Elv Thrust Sheet in the hanging wall. The style of deformation and the structures found on Kilen are caused by compressional tectonics resulting in post-extensional, presumably Early Eocene, folding and thrusting and basin inversion. The structural history of the surrounding areas and their relation to Kilen await further studies.

scholarly journals SOURCE PARAMETERS of STRONG EARTHQUAKES OCCURRED in the BAIKAL REGION and TRANSBAIKALIA in 2015

2021 ◽  
pp. 217-225
Author(s):  
A. Filippova ◽  
N. Gileva
Keyword(s):  
Baikal Region ◽  
Source Parameters ◽  
Seismic Hazard Assessment ◽  
Normal Fault ◽  
Baikal Rift Zone ◽  
Body Waves ◽  
Small Scale ◽  
Seismic Events ◽  
Study Region ◽  
Moment Tensors

We calculated seismic moment tensors in a double-couple approximation (focal mechanisms, scalar seismic moments, and moment magnitudes) and hypocentral depths for twenty earthquakes with Mw≥4.2 that occurred in the Baikal region and Transbaikalia in 2015. The initial data were amplitude spectra of Rayleigh and Love waves obtained from their records at the broadband seismic stations of the IRIS and the DK networks and first-motion polarities of body waves recorded at regional distances. A combination of the normal fault and strike-slip movements dominate in the sources of the major part of the study earthquakes. For the strongest of the considered seismic events (Mw≥4.6), the subvertical compression and subhorizontal tension in the SE-NW direction prevail, i.e. the tension is perpendicular to the main structures of the Baikal rift zone. The seismic events with Mw<4.6 are characterized by a more scattered orientation of compression and tension axis that could be caused, for instance, by stress redistribution in small-scale crustal blocks after stronger earthquakes. The obtained results are of great value for issues concerned with seismic hazard assessment and the development of geodynamical models of the lithosphere evolution of the study region.

Descriptive text to the Geological map of Greenland, 1:100 000, Kilen 81 Ø.1 Syd

2018 ◽  
pp. 1-29
Author(s):  
Kristian Svennevig ◽  
Peter Alsen ◽  
Pierpaolo Guarnieri ◽  
Jussi Hovikoski ◽  
Bodil Wesenberg Lauridsen ◽  
...  
Keyword(s):  
Hanging Wall ◽  
Field Work ◽  
Normal Faults ◽  
The South ◽  
Thrust Sheet ◽  
Basin Inversion ◽  
North East ◽  
The North ◽  
Geological Map ◽  
Surrounding Areas

NOTE: This Map Description was published in a former series of GEUS Bulletin. Please use the original series name when citing this series, for example: Svennevig, K., Alsen, P., Guarnieri, P., Hovikoski, J., Wesenberg Lauridsen, B., Krarup Pedersen, G., Nøhr-Hansen, H., & Sheldon, E. (2018). Descriptive text to the Geological map of Greenland, 1:100 000, Kilen 81 Ø.1 Syd. Geological Survey of Denmark and Greenland Map Series 8, 1-29. https://doi.org/10.34194/geusm.v8.4526 _______________ The geological map sheet of Kilen in 1:100 000 scale covers the south-eastern part of the Carboniferous–Palaeogene Wandel Sea Basin in eastern North Greenland. The map area is dominated by the Flade Isblink ice cap, which separates several minor isolated landmasses. On the semi-nunatak of Kilen, the map is mainly based on oblique photogrammetry and stratigraphical field work while in Erik S. Henius Land, Nordostrundingen and northern Amdrup Land the map is based on field data collected during previous, 1:500 000 scale regional mapping. Twenty-one Palaeozoic–Mesozoic mappable units were identified on Kilen, while the surrounding areas comprise the Late Cretaceous Nakkehoved Formation to the north-east and the Late Carboniferous Foldedal Formation to the south-west. On Kilen, the description of Jurassic–Cretaceous units follows a recently published lithostratigraphy. The Upper Palaeozoic–lowermost Cretaceous strata comprise seven formations and an informal mélange unit. The overlying Lower–Upper Cretaceous succession comprises the Galadriel Fjeld and Sølverbæk Formations, which are subdivided into six and five units, respectively. In addition, the Quaternary Ymer Formation was mapped on south-east Kilen. The Upper Palaeozoic to Mesozoic strata of Kilen are faulted and folded. Several post-Coniacian NNW–SSE-trending normal faults are identified and found to be passively folded by a later N–S compressional event. A prominent subhorizontal fault, the Central Detachment, separates two thrust sheets, the Kilen Thrust Sheet in the footwall and the Hondal Elv Thrust Sheet in the hanging wall. The style of deformation and the structures found on Kilen are caused by compressional tectonics resulting in post-extensional, presumably Early Eocene, folding and thrusting and basin inversion. The structural history of the surrounding areas and their relation to Kilen await further studies.

A study of apparent angles of emergence at Marathon Ontario from the Lake Superior data

1965 ◽  
Vol 55 (2) ◽  
pp. 405-416
Author(s):  
R. F. Mereu
Keyword(s):  
Particle Motion ◽  
Lake Superior ◽  
Seismic Events ◽  
The South ◽  
West Side ◽  
North East ◽  
The North ◽  
South West

Abstract A three component array of Willmore seismometers and a hydrophone were used to record the seismic events at Marathon, Ontario during the Lake Superior crustal experiment of 1963. The first part of each record was digitized and from an analysis of the particle motion diagrams, apparent angles of emergence of the seismic rays were determined. It was found that these angles can be used to distinguish between P2 and Pn waves. When the shot distance was less than 220 km., the first arrivals emerged with an apparent angle of 40-50°. As the shot distance was increased beyond 220 km., the rays emerged with an apparent angle of 51-70°. The apparent velocities of the (40-50) and the 51-70°) rays were 6.6 km/sec and 8.2 km/sec respectively. Further analysis of the results showed that the Moho below Marathon dipped downwards toward the south west with an angle of approximately 4°, indicating that the crust is considerably thicker on the south west side of Marathon than on the north east. A study of the ray azimuths gave some evidence of the presence of lateral inhomogeneities in the crust.

Feeding ecology of conger eels (Conger conger) in north-east Atlantic waters

2009 ◽  
Vol 90 (3) ◽  
pp. 493-501 ◽  
Author(s):  
José C. Xavier ◽  
Yves Cherel ◽  
Carlos A. Assis ◽  
João Sendão ◽  
Teresa C. Borges
Keyword(s):  
Feeding Ecology ◽  
Scomber Japonicus ◽  
Community Members ◽  
East Atlantic ◽  
Study Region ◽  
North East ◽  
The North ◽  
Helicolenus Dactylopterus ◽  
Longline Fisheries ◽  
Conger Conger

In order to understand how marine ecosystems function, it is essential to study the trophic interactions among the community members, particularly from poorly known regions. In this study, the feeding ecology and diet of conger eels,Conger conger, an abundant fish species with commercial interest, was examined in the north-east Atlantic, off Algarve (southern Portugal) between May 2005 and August 2006. The diet was characterized by species composition, size and mass of prey. Conger eels are opportunistic feeders, cannibalistic, feeding on benthopelagic/pelagic prey (67% by mass and 71% by number) but also benthic prey (32% by mass and 29% by number). Fish (67.8±4.7% in mass) are the main prey of conger eels, followed by cephalopods (16.5±3.8%) and crustaceans (15.6±3.7%). The most numerous (identifiable) fish consumed wereCapros aper, occurring in 90% of the stomach samples that contained food and representing 1.4% in mass, andScomber japonicus, the most important fish in mass (21.1%), which occurred in 4.2% of the stomach samples that contained food. The present study shows that octopodids can play a more important role in the diet of conger eels than previously thought. Of the species preyed upon by conger eels, six species (21% of the total prey taxa) are caught commercially(Trachurus trachurus, Scomber japonicus, Micromesistius poutassou, Helicolenus dactylopterusandConger conger)by local fisheries. As discards by local trawl and longline fisheries do not correspond with the diet ofC. conger, it is likely that most prey ofC. congerin rocky areas were caught actively in that study region.

The Grange of S. Anna in Montauro: The Employment of a Particular Steel-Concrete Structure in a Borderline Case of Conservation and Restoration for High Seismic Area

2010 ◽  
Vol 133-134 ◽  
pp. 861-866
Author(s):  
Michele Candela ◽  
Roberta Fonti
Keyword(s):  
Great Part ◽  
Borderline Case ◽  
Seismic Events ◽  
East Side ◽  
The Core ◽  
North East ◽  
The North ◽  
High Magnitude ◽  
Seismic Area ◽  
The Church

For at least five hundred years, the majestic grange of St. Anne in Montauro (CZ) has been overlooking the wonderful gulf of Squillace, placed at the core of Calabrian Ionic Coast. Masonry ramparts size (more than 7 metres high and 1,60 wide at the basis) together with the massive presence of four angular towers immediately hit even an inattentive beholder. Unfortunately, the predominant presence of grange results damaged by a clearly visible crack outline, which turned a great part of surrounding wall into a perpendicular heap of huge masonry portions. They appear disconnected and sheer, so that some panel systems are already collapsed on the north-east side of the building, included many internal constructions such as the church. The serious damage is not only due to repeated seismic events of high magnitude, that systematically run over this zone of Calabria. This article will describe in detail the methodologies and techniques of its making safe, considering the seismic and geological risk of the zone.

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