1,721,014 research outputs found
Lithospheric flexure, uplift and expected horizontal strain rate in the Pannonian Carpathian region
No full textThe Apuseni Mountains are located between the Pannonian Basin and the Transylvanian Basin along a direction of SE convergence with the Carpathian belt. A flexural model based on the cylindrical bending of a semi-infinite, isostatically supported, thin elastic plate is here examined with the Apuseni playing the role of flexural bulge, and under the assumption that the plate is deforming under the action of a vertical shear force and a bending moment applied at the end of the plate, beneath the Carpathians. The model yields estimates of the plate thickness ranging between 13 and 14.5 km, depending on the assumed density contrast between crust/sediments and mantle providing buoyancy. The vertical shear force which is necessary to bend the plate is in the range between 60 and 300 × 1011 N m− 1, depending on the assumed density contrast. This force is shown to be modelled by a gravitational ‘slab pull’ force, using model parameters derived from seismic tomography. If the height of the flexural bulge, after correction for erosion, is allowed to increase, the model yields an estimate of the horizontal strain rate at the top of the bulge. For example, 5 mm/yr vertical change of the flexural bulge of a 14 km thick plate results in a horizontal deformation rate of approximately 7 nanostrain/yr at the top of the bulge, a value which is at the threshold of sensitivity of continuous GPS measurements. Different vertical rates will change the horizontal strain rate almost proportionally
Average strain rate in the Italian crust inferred froma a permanent GPS network - I.Statistical analysis of the time-series of permanent GPS stations
No full textAdding geodetic strain rate data to a seismogenic context
No full textIn several seismically active areas deformation processes at depth must generate deformation at the surface, and the measurement of such surface deformation is an important boundary condition for models of the evolution of interacting blocks before, during and after earthquakes. The network of some 160 permanent GPS stations disseminated in Europe under the European Permanent Network of EUREF, with additional densification stations in particular areas such as the north east of Italy, provides a valuable contribution to the estimate of the average surface strain rate. The expected strain rate is of the order of 20-40 nanostrain per year, corresponding to a velocity change of a few mm/year over distances of some hundreds of kilometers. Consequently, we must require accuracy in the velocities of fractions of mm/year, and full control of systematic errors which may mask tectonic signals. The procedures for the systematic processing of SINEX files, representing the densified network, are reviewed here with the intent of meeting and possibly exceeding such specifications. A method for determining the noise in time series of coordinates, and of obtaining a reliable estimate of the accuracy in the estimated station velocities is described. In particular, it is shown that, on average, at least three years of continuous tracking of a permanent GPS station are required for a reliable estimate of its velocity. Then the problem of calculation of the velocity field and its horizontal gradient is addressed. We focus on the algorithm of weighted least squares collocation as a technique of minimum variance to interpolate velocities and strain rates. We present the large scale velocity flow across most of continental Europe, after subtraction of a rigid rotation approximating the generalised NE drift of Eurasia, showing a variety of intraplate and interplate processes. Finally we review the frictional model of Anderson to describe fault interaction and stress release, and present analytical expressions for recurrence times of fault instabilities. This simple framework enables a number of key problems to be identified to make proper use of the geodetically inferred strain rate data. Taking the seismicity in Friuli as a test bed, we discuss requirements on the knowledge of fault geometries, local rheology, fault plane solutions, role of pore fluid pressure and historical seismicity which, in conjunction with the surface geodetic data, are necessary to attempt a more advanced modelling of the dynamic and potentially seismogenic processes at depth
Buckling of the lithosphere in Western Himalaya: Constraints from gravity and topography data
No full textGravimetric Constraints on the Rheology of the Indian and Tarim Plates in the Karakoram Continent-Continent Collision Zone
No full textBouguer gravity anomalies in the region of the Western Himalayas, Karakoram and Tien Shan show large negative values, but classical isostatic models are insufficient to account for the detailed pattern of the observed anomalies. In the past years gravimetric surveys in the Karakoram (Marussi, Caputo and others in 1954) have been extended and densified. The full body of available gravimetric data, including the pendulum observations by De Filippi in 1913-14 and Hedin in 1929-33 have been re-analyzed. Terrain corrections have been computed systematically for all available data using an algorithm and Digital Terrain Model. The isostatic anomalies along a profile from the Indo-Gangetic foredeep, across the Karakoram Range and terminating in the Tarim Basin show the oscillating values already noticed by Marussi. This oscillatory pattern can be explained by a model in which the convergent boundaries of the Indian and Tarim plates deform by elastic flexure, besides isostacy. The gravity data ..
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