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The northern part of theWestern Carpathians suffered polyphase deformation at the boundary between their Central and Outer parts. Palaeostress analysis in the Orava region revealed the existence of five different stress fields in the period from the Late Eocene to the Quaternary. The evolution of the stress fields was determined by detailed structural analysis of the fault slip and fold orientation data. The orientation of the stress fields shows an apparent clockwise rotation from the Late Eocene to the Quaternary. During the Late Eocene to Oligocene, E-W compression and perpendicular tension affected this area. This was the time when the Central Carpathian Palaeogene Basin formed. After this compression, the palaeostress field rotated approximatly 40-50[degrees], and NW-SE compression and NE-SW tension took place in the Early Miocene. The Middle Miocene to Pliocene was characterised by progressive rotation of the palaeostress field from NW-SE to the NE-SW direction of the maximum principal compressional stress axis ([sigma][1]). This clockwise rotation of the Oligocene to Quaternary palaeostress fields here is explained by the effect of the counterclockwise rotation of the ALCAPA microplate, and by the regional stress field changes in this region. The Quaternary stress field was reconstructed on the basis of structural measurements in the Pliocene sedimentary formations of the Orava-Nowy Targ Basin. The results of the palaeostress analysis show that the Quaternary stress field is characterised by E-W-oriented S[h] (minimum horizontal compression) and N-S-oriented S[H] (maximum horizontal compression).
Knowledge of the current tectonic regime plays an essential role in natural hazard assessment, especially in the risk assessment of fault activity. Structural analysis of brittle deformations (using in version techniques) was used to determine the stress field state occurring within Pliocene and Quaternary deposits in the western part of the Central Western Carpathians. The deformation pattern of the reduced stress tensor showed that all structural measurements could be separated into two groups. An older, Late Pliocene fault population was activated un der NNW-SSE oriented extension. A younger, Quaternary fault population reflected origin in a NE–SW extensional tectonic regime and it distinctly showed a change the orientation of the S3 of about 70. The change in tectonic activity, as well as in the stress field orientation, is dated to the Pliocene-Pleis to cene boundary. The Quaternary stress field developed dur ing the post-collisional stage of the orogen. Our study shows that the West ern Carpathian internal units document NE-SW to NNE-SSW extension in the broader region around of the north ern Danube Basin.
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