Repetitive fracturing during spine extrusion at Unzen volcano, Japan
Repetitive fracturing during spine extrusion at Unzen volcano, Japan
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DOI：
10.5194/se-6-1277-2015
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发表时间：
2015-01-01
期刊：
影响因子：
3.4
通讯作者：
Lavallee, Y.
中科院分区：
文献类型：
--
作者：
Lamb, O. D.;De Angelis, S.;Lavallee, Y.
在许多形成穹丘的火山系统中，有节奏的地震活动与脊状突起有关，这是一种有据可查的现象。在日本云仙火山，1994年10月至1995年2月，一次为期4年的圆顶形成喷发以一个脊的就位结束，为进一步研究圆顶形成火山的地震过程提供了宝贵的机会。使用连续的数据记录在一个地震站位于靠近圆顶，这项研究探讨了地震活动的趋势，在脊柱的挤压。在1994年10月至1995年2月期间，我们确定了总共12208个火山地震事件。每小时的事件计数表明周期性活动与类似的40到类似的100小时，归因于定义的应变本地化和断层在导管边缘的解释性上升。波形相关性揭示了两个强集群（a.k.a.多胞胎，家庭），这是由于骨折沿着边缘浅，上升的脊椎。进一步的分析表明，在脊柱挤压以及集群源沿着脊柱边缘迁移期间，地震速度是可变的。我们对地震数据分析结果的解释得到了先前发表的现场和实验观察的支持，这表明脊柱沿着一个倾斜的管道被挤出，沿着沿着边缘发生脆性和韧性变形。我们推断，应力条件的变化作用于上，下脊柱边缘导致加深和变浅的断层源，分别。我们证明，地球物理，现场和实验证据的结合，可以帮助改善浅管道过程的物理模型。
Rhythmic seismicity associated with spine extrusion is a well-documented phenomenon at a number of dome-forming volcanic systems. At Unzen volcano, Japan, a 4-year dome-forming eruption concluded with the emplacement of a spine from October 1994 to February 1995, offering a valuable opportunity to further investigate seismogenic processes at dome-forming volcanoes. Using continuous data recorded at a seismic station located close to the dome, this study explores trends in the seismic activity during the extrusion of the spine. We identify a total of 12 208 volcano-seismic events in the period between October 1994 and February 1995. Hourly event counts indicate cyclic activity with periods of similar to 40 to similar to 100 h, attributed to pulsatory ascent defined by strain localisation and faulting at the conduit margins. Waveform correlation revealed two strong clusters (a.k.a. multiplets, families) which are attributed to fracturing along the margins of the shallow, ascending spine. Further analysis indicates variable seismic velocities during the spine extrusion as well as migration of the cluster sources along the spine margins. Our interpretation of the results from seismic data analyses is supported by previously published field and experimental observations, suggesting that the spine was extruded along an inclined conduit with brittle and ductile deformation occurring along the margins. We infer that changes in stress conditions acting on the upper and lower spine margins led to deepening and shallowing of the faulting sources, respectively. We demonstrate that the combination of geophysical, field and experimental evidence can help improve physical models of shallow conduit processes.