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971.
Alexander Garcia-Aristizabal Hiroyuki Kumagai Pablo Samaniego Patricia Mothes Hugo Yepes Michel Monzier 《Journal of Volcanology and Geothermal Research》2007
Guagua Pichincha, located 14 km west of Quito, Ecuador, is a stratovolcano bisected by a horseshoe-shaped caldera. In 1999, after some months of phreatic activity, Guagua Pichincha entered into an eruptive period characterized by the extrusion of several dacitic domes, vulcanian eruptions, and pyroclastic flows. We estimated the three-dimensional (3-D) P-wave velocity structure beneath Guagua Pichincha using a tomographic inversion method based on finite-difference calculations of first-arrival times. Hypocenters of volcano-tectonic (VT) earthquakes and long-period (LP) events were relocated using the 3-D P-wave velocity model. A low-velocity anomaly exists beneath the caldera and may represent an active volcanic conduit. Petrologic analysis of eruptive products indicates a magma storage region beneath the caldera, having a vertical extent of 7–8 km with the upper boundary at about sea level. This zone coincides with the source region of deeper VT earthquakes, indicating that a primary magma body exists in this region. LP swarms occurred in a cyclic pattern synchronous with ground deformation during magma extrusions. The correlation between seismicity and ground deformation suggests that both respond to pressure changes caused by the cyclic eruptive behavior of lava domes. 相似文献
972.
An eruption on the eastern flank of Piton de la Fournaise volcano started on 16 November, 2002 after 10 months of quiescence.
After a relatively constant level of activity during the first 13 days of the eruption, lava discharge, volcanic tremor and
seismicity increased from 29 November to 3 December. Lava effusion suddenly ceased on 3 December while shallow earthquakes
beneath the Dolomieu summit crater were still recorded at a rate of about one per minute. This unusual activity continued
and increased in intensity over the next three weeks, ending with the formation of a pit crater within Dolomieu. Based on
ground deformation, measured by rapid-static and continuous GPS and an extensometer, seismic data, and lava effusion patterns,
the eruptive period is divided into five stages: 1) slow summit inflation and sporadic seismicity; 2) rapid summit inflation
and a short seismic crisis; 3) rapid flank inflation, onset of summit deflation, sporadic seismicity, accompanied by stable
effusion; 4) flank inflation, coupled with summit deflation, intense seismicity, and increased lava effusion; and finally
5) little deflation, intense shallow seismicity, and the end of lava effusion. We propose a model in which the pre-intrusive
inflation of Stage 1 in the months preceding the eruption was caused by a magma body located near sea level. The magma reservoir
was the source of an intrusion rising under the summit during Stage 2. In Stage 3, the magma ponded at a shallow level in
the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano,
causing lava effusion. Pressure decrease in the magmatic plumbing system followed, resulting in upward migration of a collapse
front, forming a subterranean column of debris by faulting and stoping. This caused intense shallow seismicity, increase in
discharge of lava and volcanic tremor at the lateral vent in Stage 4 and, eventually the formation of a pit crater in Stage
5. 相似文献
973.
974.
大跨度斜拉桥变形监测研究 总被引:16,自引:0,他引:16
系统地介绍现代大跨度桥梁变形监测的内容、变形监测的方案与资料分析,结合武汉长江二桥的监测实践,指出利用现代测量仪器和技术,如GPS定位系统、测量机器人等不仅完全可以满足大跨度桥梁管理部门提出的要求,而且还可以提高测量速度,其测量成果也具有很高的精度。 相似文献
975.
一种附约束的单频单历元GPS双差相位解算方法 总被引:8,自引:1,他引:8
在各类变形观测中,存在着2次观测的变形值不大及各种变形方向和大小可以比较精确预测等特点,可以把这些特征作为约束条件,对GPS单历元相位观测方程进行求解。基于以上几点,提出了一种含约束条件的单频单历元GPS相位求解算法和简单实用的模糊度搜索方法,本方法据观测值直接估计模糊度参数,并根据求出的模糊度估值进行搜索,还分析了最优解的获得和检验方法,最后用2个实例说明了该法的有效性和实用性。 相似文献
976.
基于数字摄影的钢结构变形监测系统研究 总被引:3,自引:0,他引:3
讨论了基于数字摄影的钢结构变形监测系统研究所解决的主要问题,提出了相应的解决方法,并论述了整个系统的流程。 相似文献
977.
978.
979.
980.
再论拟准检定法的原理、实施和应用 总被引:2,自引:0,他引:2
综合阐述了拟准检定法的原理和特点、研究思路。拟准检定法的关键是如何正确选择拟准观测,文章介绍了初选的复选拟准观测的实施要点。列举了拟准检定法在图相关情况下的相差检测,形变分析中的异常探测以及GPS相位观测的周跳检测和修复等方面的应用例子。 相似文献