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Intra Plate Stresses Using Finite Element Modelling

Jayalakshmi S., Raghukanth S. T. G.

Acta Geophysica

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2016

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Vol. 64, no. 5

1370--1390

EN

One of the most challenging problems in the estimation of seismic hazard is the ability to quantify seismic activity. Empirical models based on the available earthquake catalogue are often used to obtain activity of source regions. The major limitation with this approach is the lack of sufficient data near a specified source. The non-availability of data poses difficulties in obtaining distribution of earthquakes with large return periods. Such events recur over geological time scales during which tectonic processes, including mantle convection, formation of faults and new plate boundaries, are likely to take place. The availability of geometries of plate boundaries, plate driving forces, lithospheric stress field and GPS measurements has provided numerous insights on the mechanics of tectonic plates. In this article, a 2D finite element model of Indo-Australian plate is developed with the focus of representing seismic activity in India. The effect of large scale geological features including sedimentary basins, fold belts and cratons on the stress field in India is explored in this study. In order to address long term behaviour, the orientation of stress field and tectonic faults of the present IndoAustralian plate are compared with a reconstructed stress field from the early Miocene (20 Ma).

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Development and inversion of Devonian and Carboniferous basins in the eastern part of the Variscan foreland (Poland)

Narkiewicz M.

Geological Quarterly

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2007

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Vol. 51, No 3

231-256

EN

The Polish part of the Central European Variscan foreland includes several regional units that differ in crustal structure and are characteried by distinct Devonian to Carboniferous subsidence and depositional histories. These units responded differently to palaeostress changes along the south ernmargin of the Old Red Continent. During the Devonian to Namurian A, areas located to the south-west of the Teisseyre-Tornquist Zone (TTZ), including the Upper Silesian Coal Basin, Małopolska and Łysogóry-Radom blocks, were influ nced by stress fields similar to those in the west ward adjacent Rheno-Hercynian Zone, whilst the Lublin Basin, located to the north-east of the TTZ, shows a similar development to the Pripyat-Dniepr-Donets rift system. After the Namurian A, the entire southern Pol ish foreland started to respond in a more consistent way to the build-up of synorogenic compressional stresses, implying a more uniform development of the stress field. During the Namurian B to early Westphalian D, the Polish foreland was dominated by north-directed compressional stresses emanating from the Southeastern Variscan Belt. During the late Westphalian and early Stephanian, the entire foreland under went compressional deformation and concomitant basin in version under the influence of stresses propagating from the Moravian-Silesian Foldand-Thrust Belt. In the Polish foreland, the development of Devonian-Carbon if erous basins, as well as the architecture of Variscan structures, clearly reflect the reactivation of preexisting crustal discontinuities, including specifically the TTZ, but also other major geophysically defined crustal bound aries. In general, thick-skinned tectonics controlled by the inherited structural grain of the basement prevailed, whereas structural decoup ling, resulting in the development of minor thrusts and reverse faulting, was of local significance only. The distinct structural-depositional development of the Pomerania region reflects its distal location with respect to the evolving orogen. Orogenic compression influenced this area only indirectly, with the TTZ acting as a guide for the transmission of transtensional and transpressional stresses.

3

Odwzorowanie powierzchni ciosowych piaskowców fliszu podhalańskiego w badaniach wytrzymałościowych z wybranych odsłonięć niecki podhalańskiej

Domonik A.

Przegląd Geologiczny

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2003

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Vol. 51, nr 5

430-435

PL

Za względu na prostą budowę geologiczną skały fliszowe Podhala, zalegające niemal połogo w strefie centralnej niecki podhalańskiej, stanowią dobry materiał do badań nad wpływem paleonaprężeń na obecny stan ośrodka skalnego za pomocą metod geomechanicznych. Efekt oddziaływania tych historycznych naprężeń jest niejako "zakodowany" w skale i przejawia się m.in. skróconym czasem przejścia fali podłużnej i poprzecznej wzdłuż kierunków odpowiadających kierunkom spękań ciosowych. Ta anizotropia ujawnia się także w trakcie badań wytrzymałościowych w postaci pękania wzdłuż pewnych, predysponowanych przez materiał skalny kierunków. Orientacje tak powstałych powierzchni spękań można korelować z orientacją powierzchni spękań ciosowych oraz z wynikami badań geomechanicznych.

EN

Due to its simple geology, the Podhale Fiysch rocks that occur almost horizontally in the central zone of the Podhale Basin are a good material for research on the paleostress impact on the current state of the rock matter by means ofgeomechanical methods. Effect of these historical stresses is "encoded " in rock and manifests itself, e.g., in the shortened time of movement of longitudinal and transverse waves along the directions corresponding to the directions of the joints. This anisotropy also reveals itself during strenght, testing, byof cracking along certain directions predisposed by the rock material. The orientations of such surfaces can be correlated with the orientations of joints as well as with the results ofgeomechanical studies.