1,720,965 research outputs found
Statistical-analysis and Clustering Features of the Phlegraean Fields Earthquake Sequence (may 1983-may 1984)
No full textA Linear Intensity Model To Investigate the Causal Relation Between Calabrian and North-aegean Earthquake Sequences
No full textSource Parameter Analysis From Strong Motion Records of the Friuli, Italy, Earthquake Sequence (1976-1977)
No full textA model for earthquake generation during unrest episodes at Campi Flegrei and Rabaul calderas
No full textWe have analysed the seismicity that occurred at Campi Flegrei caldera (Italy) in the period 1982-1984, during an unrest episode. Earthquake locations describe a system of inward dipping ring faults. Focal mechanisms of such events show a normal dip component, which is not in agreement with the differential uplift of the inner caldera, as defined by static ground deformations. We have performed a simulation of the stress field generated by overpressure in a magma chamber in presence of lateral discontinuities, using a boundary element method. Lateral discontinuities simulate the ring fault system marking the border of the inner caldera collapse. Results allow us to hypothesize that reverse fault slip on the ring fault is mainly aseismic, and such aseismic movement is able to focus normal fault shear stress along the lateral discontinuities. Aseismic slip on the ring fault in response to static deformation is also supported by the low seismic moment released (M-0 congruent to 10(15) Nm), about two orders of magnitude lower than expected from the shear slip on the discontinuities needed to accomplish the total static surface deformation (1.8 m). Such results have been compared with observations at Rabaul caldera, during a similar unrest episode. In this area, the seismic moment release is in good agreement with shear slip produced on a system of outward dipping ring faults, and seismicity is much more focused on the fault structures. Such a different behaviour can be interpreted, in the framework of our model, as due to the different sign of the stress normal to the ring faults, for inward and outward dip. The comparison between the two areas shed new light about the dynamics of earthquakes in calderas, in terms of the role played by ring fault systems
Scaling of Peak Ground Motions From Digital Recordings of Small Earthquakes At Campi Flegrei, Southern Italy
No full text
Accurate fault mechanism determinations for a 1984 earthquake swarm at Campi Flegrei caldera (Italy) during an unrest episode: Implications for volcanological research
No full textWe 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
Increased tumor cell multiplication after radiofrequency lesions in median hypothalamus in the mouse and rat
No full textA significant increase of cell multiplication in inoculated ascitic and solid tumors was demonstrated in both DBA/2 and C57BL/6 mice as well as in Wistar rats after radiofrequency lesions in the median hypothalamus (ventromedial and dorsomedial nuclei; part of arcuate nucleus). The following tests were performed: Mitotic and metaphasic index, doubling time of tumor, incorporation of tritiated thymidine into DNA, cell cycle parameters and growth fraction. The increased rate of cell proliferation measured was predominantly due to the higher speed of DNA biosynthesis with a minor contribution by an increase of the growth fraction. In the animals with hypothalamic lesions we demonstrated a slight decrease in the secretory activity of the adenohypophysis. Because it is generally stated that failure of hypophysis function hinders cell multiplication in normal and neoplastic tissues, we think that heightened cell proliferation after hypothalamic lesions is due to suppression of an inhibitory mechanism located in the hypothalamus and which is independent of the hypophysis
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