Modelling of the ground motion of the maximum probable earthquake and its impact on buildings, Vilnius city

The Baltic region is characterised by a low seismic activity. The recent Kaliningrad earthquake of magnitude M= 5.0 in 2004 persuades that the previous estimates of the seismic hazard of the Baltic region were underrated. It urges the re-assessment of characteristics of the maximum possible earthquake that may take place elsewhere in the Baltic region. The Kaliningrad earthquake scenario was modelled for Vilnius city area. It is motivated by occurrence of several moderate historical earthquakes that took place close to the city, also the presence of some large-scale fault zones in proximity to the city. The maximum probable earthquake of magnitude M= 5.0 and hypocentral depth of 15 km was modelled to take place in Vilnius city area. The modelled seismic response spectra are dominated by low frequencies 2-5 Hz that is accounted to soft soil effect. The peak ground acceleration (PGA) was modelled to range from 1.05 m/s2 to 1.40 m/s2 depending on soil type, i.e. moraine dominated and sand/technosoil dominated, and on stress-strain relationship (linear vs. non-linear soil behaviour). Estimated PGA corresponds to macroseismic intensity Io= 7 (MSK-64) implying only minor building damages. The modelled seismic signal implies that 2-10 store buildings are subject to the highest (though modest) seismic risk

Origin of the Great Nemunas Loops, South Lithuania

The Nemunas River, one of the largest rivers of the Baltic region, is characterised by a generally straight valley. In the middle part of its course the Great Nemunas Loops are distinct features that occupy an area of 320 km2 near the Birštonas Resort. The Nemunas valley here is 1.5‑5 km wide and 45‑80 m deep. The loops are cut into a glaciolacustrine plain confined between glacial and deltaic relief complexes and formed during the two last phases of glaciation. The origin of the entrenched loops, as large as 6‑10 km, can not be explained in conventional terms of river meandering. The activity of underlying tectonic structures is the major factor, the Great Nemunas Loops being confined to the Birštonas tectonic depression. Despite their small magnitudes the neotectonic structures within the depression significantly influenced the glacial and meltwater sedimentation (hence, the topography) that controlled the geometry of the Nemunas valley. The initial sinuosity of the valley was only a little enhanced by later lateral erosion. Fault activity is indicated by numerous mineral water springs and straight channel segments. Only a few sites of similar mineral water discharge are documented in Lithuania, suggesting the specific structural setting of the Great Nemunas Loops. Inspection of drill cores revealed the inheritance of the Nemunas valley from underlying paleovalleys of Eemian and Holsteinian Interglacials, implying persistence of the controlling factors.Le fleuve Nemunas, un des plus grands fleuves de la région baltique, est caractérisé par une vallée généralement rectiligne. À la mi-course du Nemunas, les Grandes Boucles occupent un territoire de 320 km2 dans la zone de villégiature de Birštonas. Ces méandres, d’une largeur de 6 à 10 km, entaillent une plaine glaciolacustre confinée entre des complexes glaciaires et deltaïques formés au cours des deux dernières phases de déglaciation. À cet endroit, la vallée du Nemunas a une largeur de 1,5 à 5,0 km et une profondeur de 45 à 80 m. L’origine de ces boucles profondes ne peut être imputée aux processus habituels de formation de méandres. L’activité des structures tectoniques sous-jacentes est le principal facteur à l’origine de leur formation. Les Grandes Boucles du Nemunas sont confinées à la dépression tectonique de Birštonas, sur laquelle se sont formées des structures néotectoniques de moindre ampleur. Ces dernières ont néanmoins eu une influence significative sur la sédimentation glaciaire et celle associée aux eaux de fonte (et sur la topographie) qui a influencé la géométrie de la vallée du Nemunas. La sinuosité initiale de la vallée n’a été que peu accentuée par l’érosion latérale ultérieure. L’activité des zones de faille est décelée par la présence de nombreuses sources d’eau minérale et le redressement de certains segments du fleuve. Seuls quelques sites ayant des sources minérales similaires sont connus en Lituanie, ce qui met en relief la singularité structurale des Grandes Boucles du Nemunas. L’examen des carottes de forage révèle la filiation entre la vallée actuelle du Nemunas et les paléovallées interglaciaires de l’Eemien et du Holsteinien sur lesquelles elle repose

Correlation of shear-wave velocities and cone resistance of quaternary glacial sandy soils defined by Seismic Cone Penetration Test (SCPT)

The derivation of dynamic geotechnical parameters of soil are of primary importance in designing specific structures. Direct measurements are expensive and time-consuming. In this study the correlation between the seismic wave velocities and cone resistance was derived from seismic cone penetration testing (SCPT) of Quaternary glacial sandy soils in Lithuania. The close relationship was obtained for sandy soils indicating wide range of cone resistance and seismic wave velocities. The correlation is as high as R = 0.80. The derived regression equation could be reasonably used in assessing dynamic geotechnical and seismic parameters in Lithuania and other territories characterized by similar geological conditions using conventional cone penetration testing (CPT) method. It enables consistent geotechnical and seismic zoning of sandy soils

Correlation between shear wave velocity and cone resistance of Quaternary glacial clayey soils defined by Seismic Cone Penetration Test (SCPT), Lithuania

The correlation between the cone resistance and the shear wave velocities was derived for the Quaternary glacial clayey soil (moraine) using Seismic Cone Penetration Test (SCPT) technique. The correlation obtained between two parameters is as high as +0.73. The derived regression equation has significant differences from those of clayey soils reported from other regions that are accounted to different genetic type of sediments and evolutionary history. Accordingly the obtained results can be applied in defining the dynamic geotechnical properties of glacial clayey soils of Lithuania and other regions that have similar geological conditions (i.e. formerly glaciated areas)

Sensitivity of dynamic behaviour of the FE model: Case study for the ignalina NPP reactor building

The 3D thin‐walled finite element model of Ignalina NPP Unit 2 reactor building was developed aimed at the evaluation of the global dynamic behaviour with a focus on the seismic response. The model comprises description of the monolithic structures, while prefabricated frame structures are ignored and replaced by external masses. Sensitivity study of the selected dynamic characteristics of the model with respect to data uncertainties is considered. Uncertainty of the model is considered in terms of masses of removed structures and wall stiffness. Seismic input is represented by the site specific free‐field ground response acceleration spectra. The sensitivity study concerns variations of frequencies and acceleration of in‐structure horizontal response spectra at specified points. Maximal bending moments are also considered. It was obtained that the reactor level is not sensitive to the uncertainties considered, while discernable sensitivity was detected at the top level of the structure. Santrauka Pateikta Ignalinos atominės elektrinės pastato erdvinio baigtinių elementų dinaminio modelio kūrimo koncepcija, išnagrinėtas šio modelio jautrumas keičiamoms masėms ir sienų standumui. Parodyta, kaip šie keičiami dydžiai turi įtaką dažniams, horizontaliems tam tikrų nagrinėjamų taškų atsako spektrams, lenkimo momentų persiskirstymui ir jų didžiui. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: Ignalinos AE, baigtinių elementų modelis, savųjų dažnių ir seisminė analizė, plyno lauko spektras, atsako spektras

Predicting porosity through simulating quartz cementation of Middle Cambrian sandstones, West Lithuania

Quartz cementation is a major parameter controlling the reservoir properties of the Middle Cambrian quartz arenites of the central and western parts of the Baltic Basin. Marked local variations in the porosity and permeability severely complicate oil exploration and exploitation inWest Lithuania. Commonly, the porosity of the oil reservoirs is 6–8%. Therefore even minor changes in the porosity have a considerable impact on the potential of oil fields. A predictive model of the quartz cementation is proposed, based on kinetic modelling results. The precipitation rate-limiting model effectively explains sharp variations in quartz cementation controlled by grain-size changes. The model was further improved by incorporating the sorting factor. Even so, the amount of quartz cementation is overpredicted by 4–7% in some intervals, implying that the precipitation rate-limiting model is too simplified. A good correlation was obtained between stylolite spacing and quartz cementation, the overpredicted quartz amount increasing with an increase in stylolite spacing. The modelling results argue against any discernable impact of the oil on the reservoir quality of the sandstones. The successful prediction of reservoir quality mainly depends on correct reconstruction of the sedimentary environment of the Middle Cambrian deposits. The evolutionary model of the quartz cementation suggests a good reservoir quality of the Cambrian sandstones during the later part of Late Palaeozoic, when most of oil was generated in the basin

Supracrustal suite of the Precambrian crystalline crust in the Ghor Province of Central Afghanistan

AbstractThe Proterozoic pre-Ediacaran metamorphic basement of the southern Tajik (North Afghanistan) continental block and the adjacent Band-e-Bayan zone is exposed in the Ghor Province of Central Afghanistan. It is predominantly composed of the EW-striking supracrustal succession consisting of interbedded felsic schists and gneisses (metapsammites), amphibolites (metabasalts), calcite and dolomite marbles. The metamorphic facies changes from greenschist in the Band-e-Bayan zone to amphibolite facies in the Tajik block. The supracrustal rocks of the Band-e-Bayan zone and Tajik block possess common features suggesting that the former represents a tectonized part of the latter. The geochemical characteristics of metapsammites indicate derivation of the clastic material from a continental arc and, partly from a passive continental margin, whereas the composition of metabasalts suggests their possible formation in a continental rift basin. The tectonic setting of supracrustal unit could be interpreted as a back-arc type basin. We presume that the Tajik microcontinent split off the Gondwana supercontinent along an ancient rift zone during the late Paleozoic

Upgraded map of Bouguer anomalies of Lithuania based on GIS techniques

The presently used Bouguer anomaly map of Lithuania is based on gravity field mapping of 1958-1961. The constant density 2,30 g/cm3 between the Earth’s surface and reference level (sea level) was employed to calculate Bouguer anomalies. The digital model of the gravity field compiled at the Lithuanian Geological Survey in 1997 also incorporates the same value. The extensive drilling data show, however, that lithology of the upper layers represented by the Quaternary glacial and interglacial deposits overlying the Prequatemary sediments of different composition is highly complex. Accordingly, the density profile also varies drastically across the country, even at the local scale. It significantly reduces the accuracy of the calculated gravity anomalies. The new method based on application of GIS techniques is proposed for more correct evaluation of the reduction densities. The density map was derived from 13,222 borehole data stored at the digital database “Geolis” of Lithuanian Geological Survey. Density map was calculated using Mapinfo software. The lower densities were obtained for most of the Lithuanian territory. The newly obtained values were automatically assigned to the gravity sites and the upgraded Bouguer anomaly map was re-compiled. The general shape of the map is rather similar to that of the old version. However, the difference between the local anomalies of the new and the old models attains 0,5-3 mGal that is rather considerable. The proposed technique can be applied in other regions. Also, the new Bouguer anomaly map allows recalculation of other geoparameters (eg geoid map). Article in Lithuanian Bouguer anomalijų žemėlapio patikslinimas GIS priemonėmis Santrauka. Gravitacinio lauko variacijas geriausiai atspindi Bouguer anomalijų žemėlapis, kuri sudarant, be kitų parametrų, labai svarbu žinoti tarpinio sluoksnio, t. y. sluoksnio, esančio tarp Žemes paviršiaus ir jūros lygio, tankį. Pagal priimtą metodiką Lietuvos Bouguer anomalijų žemėlapis sudarytas įvedus pastovų 2,30 g/cm3 tankį. Tačiau geologiniai tyrimai rodo, kad viršutiniams sluoksniams būdingas labai ryškus uolienų sudėties ir atitinkamai tankio kitimas, todėl dabar naudojamas gravitacinio lauko žemėlapis nėra visai tikslus. Anomalijų laisvajame ore ir aukščiu koreliacija rodo, kad vidutinis tarpinio sluoksnio tankis yra gerokai mažesnis (mažesnis nei 2,24 g/cm3). Straipsnyje pateikiama nauja tarpinio sluoksnio tankiu įvertinimo, taikant GIS technologijas, metodika. Pagal iš 13 222 gręžinių gautą informaciją sudarytas detalus tankių žemėlapis. Šie duomenys automatiškai pervesti į gravitacinius stebėjimo taškus, atitinkamai perskaičiuotas Bouguer anomalijų žemėlapis. Masių deficitas, palyginti su ankstesniu tarpinio sluoksnio modeliu, kinta nuo +10 000 kg/m2 Šiaures Lietuvos centrinėje dalyje iki –30 000 kg/m2 — –50 000 kg/m2 didžiojoje Lietuvos dalyje. Atitinkamai gerokai pakoreguotos ir Bouguer anomalijų reikšmes. Skirtumas siekia net 2–3 mGal Baltijos aukštumose, 0,5–1 mGal Žemaitijos aukštumose ir –0,5 mGal Šiaures Lietuvos centrinėje dalyje. Siūloma metodika galima plačiai taikyti ir kituose regionuose tikslinant gravitacinio lauko žemėlapius. Be to, tai leidžia koreguoti ir kitus gravitacinio lauko žemėlapius (pvz., nustatant geoidą). Raktažodžiai. Bouguer anomalija, gravitacinis laukas, GIS, tarpinio sluoksnio tankis