Stress field

About: Stress field is a research topic. Over the lifetime, 11926 publications have been published within this topic receiving 226417 citations.

Present-day stress field and active tectonics in southern peninsular Italy

Abstract: SUMMARY A systematic collection of present-day stress directions has allowed us to gain new insights into the recent tectonic evolution of the Italian Peninsula. Horizontal stress directions from breakouts in 40 deep wells drilled for oil exploration have been compared to compressional and tensional axes of 17 earthquake fault-plane solutions (4.2 < M < 7) and 17 stress axes obtained from structural analysis on Quaternary rocks. Notwithstanding the different scales and depths of the data considered in this worknear-surface for structural data, 0-6 km depth for breakouts, GZ 3-20 km for earthquake focal mechanisms-the three distributions are surprisingly similar, all showing a predominant northeast-directed minimum horizontal stress in a broad region from the Tyrrhenian backarc through the Apenninic belt and up to the Apulian foreland. The belt, which corresponds to a region of high elevation, contemporary uplift and strong seismic release, with earthquakes as large as M=7, is characterized by a normalfaulting stress regime. The breakout data demonstrate that the NE-oriented extension associated with the seismogenic normal faults of the southern Apennines is determined by a regional stress with o,=NE, in agreement with the seismological evidence that these faults are young ( post-Middle Pleistocene). The breakout data show that even the foredeep and the most internal foreland region, where the ( Apulian) foreland crops out, are dominated by northeast-oriented extension, even if we cannot establish the stress regime of this region due to the lack of seismicity. This suggests that a model in which the underthrusting Adriatic plate is in compression and in flexure, generating extension in the upper (Apenninic) plate, is not applicable, unless what we observe (NE-directed Shmin) is limited to the upper part of the Adriatic plate, while its deeper portion might be in compression. Compared to the recent compressional tectonics that affected parts of the study region in the Upper Pliocene and Lower-Middle Pleistocene, it seems likely that an important change in the stress field occurred in this area during the Quaternary, most probably around 0.7 Ma. Considering the main tectonic processes acting in southern Italy-NNW convergence between Africa and Eurasia and subduction of Ionian and Adriatic lithosphere with associated slab pull and back-arc riftingwe speculate that the extension observed in southern peninsular Italy can be explained either by a slab window or by a buoyant subducted continental lithosphere in the upper mantle between the two active arcs, the northern Apennines and the Calabrian arc.

In situ stress, natural fracture distribution, and borehole elongation in the Auburn Geothermal Well, Auburn, New York

Abstract: Hydraulic fracturing stress measurements and a borehole televiewer survey were conducted in a 1.6-km-deep well at Auburn, New York. This well, which was drilled at the outer margin of the Appalachian Fold and Thrust Belt in the Appalachian Plateau, penetrates approximately 1540 m of lower Paleozoic sedimentary rocks and terminates 60 m into the Precambrian marble basement. Analysis of the hydraulic fracturing tests indicates that the minimum horizontal principal stress increases in a nearly linear fashion from 9.9±0.2 MPa at 593 m to 30.6±0.4 MPa at 1482 m. The magnitude of the maximum horizontal principal stress increases in a less regular fashion from 13.8±1.2 MPa to 49.0±2.0 MPa over the same depth range. The magnitudes of the horizontal principal stresses relative to the calculated overburden stress are somewhat lower than is the norm for this region and are indicative of a strike-slip faulting regime that, at some depths, is transitional to normal faulting. As expected from the relative aseismicity of central New York State, however, analysis of the magnitudes of the horizontal principal stresses indicates, at least to a depth of 1.5 km, that frictional failure on favorably oriented preexisting fault planes is unlikely. Orientations of the hydraulic fractures at 593 and 919 m indicate that the azimuth of the maximum horizontal principal stress at Auburn is N83°E±15°, in agreement with other stress field indicators for this region. The borehole televiewer log revealed a considerable number of planar features in the Auburn well, the great majority of which are subhorizontal (dips < 5°) and are thought to be bedding plane washouts or drill bit scour marks. In addition, a smaller number of distinct natural fractures were observed on the borehole televiewer log. Of these, the distinct steeply dipping natural fractures in the lower half of the sedimentary section at Auburn tend to strike approximately east-west, while those in the upper part of the well and in the Precambrian basement exhibit no strong preferred orientation. The origin of this east-west striking fracture set is uncertain, as it is parallel both to the contemporary direction of maximum horizontal compression and to a late Paleozoic fracture set that has been mapped to the south of Auburn. In addition to these planar features the borehole televiewer log indicates paired dark bands on diametrically opposite sides of the borehole throughout the Auburn well. Processing of the borehole televiewer data in the time domain revealed these features to be irregular depressions in the borehole wall. As these depressions were consistently oriented in a direction at right angles to the direction of maximum horizontal compression, we interpret them to be the result of stress-induced spalling of the borehole wall (breakouts).

Estimating residual stress in the restrained ring test under circumferential drying

Abstract: The restrained ring test is becoming widely used as a standard test method to assess the potential for early-age cracking in concrete mixtures. Previous research focused on the development of analytical solutions for quantifying residual stress development in restrained ring specimens that either assumed that the ring was thin (i.e., a thin wall approximation) or that the shrinkage was uniform along the radial direction for a thick-walled ring. This paper presents an analytical solution to consider the influence of moisture gradients that occur when a thick-walled ring specimen dries from the outer circumference. Toward this end, the ring that dries from the outer circumference is treated as the superposition of a stress field that is caused by external restraint and a stress field that arises due to differential shrinkage. An analytical expression is presented to estimate the stress components. To assess the suitability of the analytical solution, it was compared with results from a finite element analysis and a reasonably good agreement was observed.