We present a new model of crustal deformation in the Pamir–Tien Shan region. There are two different ways of assessing the deformation: block and continuum modeling. In this study we adopt a continuum modeling approach, which is based on computation of the two-dimensional strain rate tensor field of the Earth’s crust. This approach allows independent computation of the deformation at any point of the computation grid by solving an over-constrained system of linear algebraic equations based on the linear term of the Taylor series expansion of the point velocity function about its radius-vector. We propose a detailed description of this method including a significance criterion introduced by the author for estimating the reliability of modeling results. We discuss the parameters of this deformation model for the Pamir–Tien Shan region, computed from the GPS velocity data measured at 506 sites of the Central Asian GPS network. The most distinctive features of the estimated strain field are N–S shortening of the largest basins in the Tien Shan and at the junction between the Pamir and Tien Shan, as well as the westward motion of the eastern and western boundaries of the Pamir relative to the Tarim plate and Tajik depression.
Active reactions of embryonic tissues to mechanical forces play an important role in morphogenesis. To study these reactions, experimental models that enable to evaluate the applied forces and the deformations of the tissues are required. A model based upon the active intrusion of a living early gastrula Xenopus embryo into a tube half the embryo in diameter is described. The intrusion is initially triggered by a suction force of several dozen Pa but then continues in the absence of external driving force, stopping immediately after the entire embryo has penetrated into the tube. The process can be stopped by cytoskeletal drugs or by the damage of the part of the embryo still non-aspirated and is associated with the transversal contraction and meridional elongation of the non-aspirated part of the embryo surface and quasi-periodic longitudinal contractions/extensions of the cells within the part already aspirated. We suggest that this reaction is an active response to the embryo deformation and discuss its morphogenetic role. The problem of estimating the elastic modules of embryonic tissues is also discussed.
Abstract:The Bishkek geodynamic polygon (BGP,.5° N -73-77° E) is located within the central segment of the North Tien Shan seismic zone, in the junction zone of the Tien Shan orogene and the Turan plate ( Fig. 1). In the entire modern structure of Tien Shan lengthwise zones of shearing (with both right-and left-lateral strike-slip faults) are observed, thus Tien Shan can be considered as a transpression zone. Our study aimed at comparing deformation values estimated for the BGP territory from the seismic and GPS data. The modern stress-strain state of the study area was determined from the focal mechanisms of 1287 earthquakes that occurred in the period from 1994 to 2015. The study area was divided into cells with a radius of 0.2° (~20 km). The cell centers were in the nodes of the grid with a spacing of 0.1° (~10 km). A tensor of a seismotectonic deformation (STD) rate within a cell was calculated as a sum of seismic moment tensors normalized for time, volume and shear modulus, assuming that STD is similar at different scale levels. The STD field is shown in Figure 4 at the background given by the deformation intensity pattern. Figure 6 shows the scatter of the sums of the strain rate tensor's horizontal components estimated from the seismic data. The modern crustal movements were estimated from the geodetic measurements performed on the Central Asian GPS Network. Using the crustal movement velocities for 90 sites in the study area, the deformation processes in the crust were modeled based on the linear part of the Taylor expansion of the point's-velocity-versus-its-radius-vector function. Then the velocity gradient tensors were estimated for the grid nodes with a spacing of 8.3 km. To estimate tensor's value in every single grid node a system of linear algebraic equations was solved by the weighted least-squares method. The weight of an observation point decreased with an increasing distance to such point, so that the inhomogeneity of the deformation field could be taken into account. From the velocity gradient tensors we calculate the strain rate tensors (Fig. 5) and then the rate of changes of the area (meterage) ∆ (Fig. 7). A comparison of Figures 4 and 5 shows a general coincidence between the directions of compression/shortening axes estimated from the seismic and GPS data. On average, the STD intensity is by two to three orders lower than the deformation intensity assessed from the GPS data. It can be explained by the fact that the horizontal components of the total deformation amounts visible in the GPS data are actually the sums of aseismic and coseismic components, and the deviator part of coseismic component was considered as STD. Comparing the fields of the sums of the strain rate tensor's horizontal components from the seismic data (Fig. 6) and the GPS data (Fig. 7) reveals an inconsistency for the Suusamyr depression: the GPS data shows a considerable crustal shortening in the horizontal plane, while the seismic data is indicative of a shear deformation. In the central part of the junction zone of...
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