Volcanomagnetic effects at Vulcano Island (Aeolian archipelago, Italy)
Volcanomagnetic effects at Vulcano Island (Aeolian archipelago, Italy)
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武尔卡诺岛（意大利风神群岛）的火山磁效应
DOI：
10.1046/j.1365-246x.2000.00987.x
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发表时间：
2000
影响因子：
2.8
通讯作者：
F. Ferrucci
中科院分区：
文献类型：
--
作者：
C. Negro;F. Ferrucci
1990年11月至1991年12月在武尔卡诺岛安装了两个连续运行的质子磁力计，两个磁力计相距2公里，每5分钟同时取样一次，从而探测到一些被认为是火山物理状态内部变化造成的瞬时异常。在测量期间，两个台站磁场平均值的差异经历了2 nT的缓慢变化。一站总强度均值与两站总强度均值差呈负相关。这表明，瞬态磁场对信号的贡献可以分为两部分：一部分是外部来源，这对两个站点来说是相同的，另一部分是内部来源，与前者成比例，但取决于站点。根据对磁场的简单描述，开发了一种分析方法，以区分火山磁源瞬变和外部瞬变磁场强烈变化产生的瞬变。考虑到两个台站测量值之间的相关性，进行了精确的分析，结果挑出了三个磁异常（1991年4月2日、7月18日和12月23日）。将实验数据与1991年在武尔卡诺发生的地震列表进行比较，表明磁异常与地震之间存在密切的时间对应关系。异常的振幅（2和4 nT之间），空间范围（约2公里）和极性指向压磁eVect作为驱动这些瞬态变化的主要物理机制。另一方面，相对于区域场的异常，观察了一年多，是可以解释的热磁eVect检测在两个站。位于拉福萨火山口下1300米深处的半径为250米的完全消磁球形源产生的静磁异常与在武尔卡诺观测到的缓慢变化一致。
SUMMARY The installation of two continuously operating proton magnetometers, 2 km apart and sampling simultaneously every 5 min, on Vulcano Island from 1990 November to 1991 December allowed the detection of some transient anomalies thought to result from internal variations in the physical state of the volcano. The diVerence of mean values in the magnetic field at the two stations underwent a slow variation of 2 nT during the period of measurements. The mean values in the total intensity at one station were inversely correlated to the diVerence between the mean values of the two stations. This suggests that the contribution to the signal generated by the transitory magnetic field may be broken down into two parts: one of external origin, which is identical for both stations, and another of internal origin, proportional to the former, but dependent on the site. Following on from this simple description of the magnetic field, a method of analysis was developed to distinguish between transients of volcanomagnetic origin and transients generated by strong variations in the external transitory magnetic field. An accurate analysis, which takes into account the correlation between the measurements at the two stations, leads to the singling out of three magnetic anomalies (on 1991 April 2, July 18 and December 23). Comparison of the experimental data with the list of earthquakes occurring at Vulcano during 1991 showed the close temporal correspondence between the magnetic anomalies and earthquakes. The amplitude (between 2 and 4 nT), spatial extent (approximately 2 km) and polarity of anomalies point to the piezomagnetic eVect as the primary physical mechanism driving these transient changes. On the other hand, the anomaly with respect to the regional field, observed over one year, is explicable in terms of a thermomagnetic eVect detected at both stations. The magnetic static anomaly produced by a completely demagnetized spherical source, of 250 m radius located under the La Fossa crater at a depth of 1300 m, is in agreement with the slow changes observed at Vulcano.