Dikes within stratovolcanoes are commonly expected to have radial patterns. However, other patterns may also be found, due
to regional stresses, magmatic reservoirs and topographic variations. Here, we investigate dike patterns within volcanic edifices
by studying dike and fissure complexes at Somma-Vesuvius and Etna (Italy) using analogue models. At the surface, the dikes
and fissures show a radial configuration. At depths of tens to several hundreds of metres, in areas exposed by erosion, tangential
and oblique dikes are also present. Analogue models indicate that dikes approaching the flanks of cones, regardless of their
initial orientation, reorient to become radial (parallel to the maximum gravitational stress). This re-orientation is a significant
process in shallow magma migration and may also control the emplacement of dike-fed fissures reaching the lower slopes of
the volcano. 相似文献
Shallow strike slip earthquakes on vertical faults are modelled as two-dimensional antiplane strain ruptures in a uniformly prestressed homogeneous halfspace. Behind the rupture front, which is specified, the stress drops to a lower value. The elastodynamic boundary value problem is solved with a finite difference method. Several cases are studied, which include symmetric and one-directional rupture propagation, surface faulting, multiple events, variable rupture velocity, sticking and rebreaking of the fault plane. The time function of displacement, velocity and acceleration are interpreted as signals generated by events in the focus, namely starting, stopping and breaking through the surface of the rupture. The model explains peak velocity and peak acceleration in the near field of M5.5–6 earthquakes; which are typically about 0.2 m/s and 5 m/s2 at 10 km epicentral distance, if the rupture velocity is close to the shear wave velocity. Sticking of the fault does not alter the accelerograms significantly, but it increases the seismic moment in simple events and decreases it in multiple events.Contribution No. 226, Geophysical Institute, University of Karlsruhe. 相似文献
Hydraulic fracturing is a key technology for unconventional oil and gas exploration. In the process of hydraulic fracturing, the interaction of hydraulic fractures and natural fractures to form a complex fracture network is the premise for the efficient exploitation of unconventional oil and gas, and the design of perforation scheme has an important impact on the complexity of the fracture network. In order to further study the evolution mechanism of the fracture network, simulate the fracture propagation process of the real jointed fractured rock mass in hydraulic fracturing, and optimize the perforation plan scientifically and reasonably, this paper adopts the method of global embedding of cohesive elements, and uses Python to carry out the second development. A DFN discrete fracture network was created, and a natural fracture model of the rock mass considering the discrete fracture network was established. At the same time, the models without DFN discrete fracture network were set under the same conditions for comparison, and the influence of different angles of perforation schemes on the fracturing effect was studied. The acoustic emission localization map and acoustic emission energy data during the loading process are extracted by MATLAB programming, and the crack rupture mechanism and propagation process are further analyzed. The results show that the activation of natural fractures is affected by the stress shadow generated between perforations and the angle between perforations and natural fractures; the distribution law of natural fractures in shale is identified, and the angle between perforation and natural fractures is improved to make hydraulic fractures easier. It communicates with and spreads along the natural fractures to form a complex fracture network. 相似文献
