Analysis of Stress Distribution in Torsional Shear Testing

The research described herein is concerned with the establishment of a specimen geometry that will lead to a more uniform stress distribution in cyclic torsional shear testing. This goal is realized by means of a parametric study using the method of finite elements and a homogeneous, isotropic, linear-elastic soil characterization. The results of these analyses provide a good qualitative measure of the relative effects of the several parameters under consideration. On the basis of the parametric study, design charts are developed which enable an appropriate specimen geometry to be selected for any specified degree of stress uniformity

Accurate fault mechanism determinations for a 1984 earthquake swarm at Campi Flegrei caldera (Italy) during an unrest episode: Implications for volcanological research

We have analyzed 42 microearthquakes (1 < M(L) < 3) that occurred at Campi Flegrei volcanic area during an intense swarm-like activity (more than 500 events in half a day) in the last period of strong ground uplift (1982-1984). Focal mechanisms of these earthquakes have been computed by a probability method, which uses P wave polarity and S wave polarization data, Composite focal mechanisms for different groups of earthquakes have also been computed by the same technique, Results show a well-defilled fault plane, in agreement with the elongation of the epicentral pattern, The orientation and dip of this fault plane, together with other observations about hypocenter locations and focal mechanisms of the whole seismicity accompanying the ground uplift episode, suggest the presence of an elliptical fracture system at the caldera center, This fracture system, dipping toward the center of the caldera, should represent the limit of the most recent caldera collapse, which is also indicated by a negative Bouguer gravity anomaly, Moreover, an important differential feature among various groups of earthquakes has been shown, namely, a rotation up to about 30 degrees of the strike of the compressive stress axis, between the easternmost and the westernmost events, The resulting pattern indicates that the axis is always oriented towards the town of Pozzuoli, which roughly represents the very center of the caldera, and also the center of symmetry of the ground deformation, These observations strongly suggest that earthquakes are generated by the variation of the stress field associated with the deformation, along prefractured zones, because of their greater weakeness. This study provides, then, the first direct evidence that both seismicity and ground deformations have a common origin

Modal parameter tuning of an axisymmetric resonator via mass perturbation

© 2015 IEEE. This paper reports the permanent frequency mismatch reduction of the primary wineglass modes in a planar axisymmetric resonator by strategic mass loading. The resonator consists of a set of concentric rings that are affixed to neighboring rings by a staggered system of spokes. The outer layers of spokes are targets for mass deposition. This paper develops modified ring equations that guide the mass perturbation process, and despite the fact that the deposited mass and deposition locations are quantized, it is possible to systematically reduce the frequency difference of the wineglass modes to effective degeneracy such that two modes cannot be distinguished in a frequency response plot. Results on five resonators are reported with nominal wineglass modes near 14 kHz, quality factors of 50k, and frequency mismatches exceeding 30 Hz in some cases, but with postperturbation mismatches smaller than 80 mHz. Furthermore, it is also shown that the quality factors remain unchanged