Currenti Gilda, Bonaccorso Alessandro
Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Etneo, Sezione di Catania, Italy.
Sci Rep. 2019 May 17;9(1):7553. doi: 10.1038/s41598-019-44066-w.
Unprecedented ultra-small strain changes (~10-10), preceding and accompanying the 2017 explosive-effusive activity, were revealed by a high precision borehole strainmeter at Etna. No pre- or co-eruptive deformation was detected by the GPS measurements, which often fail to detect ground deformation engendered by short-term small volcanic events due to their limited accuracy (millimetres to few centimetres). Through the analysis and detection of ultra-small strain changes (few tens of nanostrain), revealed by filtering the raw data, a significant time correspondence with the eruptive activity is observed. For the first time, cyclic fast exponential strain changes, preceding the onset of eruptive events, with a timescale of about 2-7 days, were detected. These variations are attributable to the expansion of the shallow magma reservoir, which is replenished with new magma from depth during the inter-eruptive periods. Interpreting the strain changes in terms of pressurization/depressurization of the chamber due to the cyclic influx and withdrawal of magma, allows placing some constraints on the magma recharge volume rate. A Finite Element model has been developed to simulate the temporal evolution of the strain changes generated by the re-pressurization of a spheroidal magma source using a dynamical approach. An average total mass budget of about 1-2 × 10 kg, which is in the range of the erupted mass, is estimated to be accumulated within a shallow vertically elongated magma chamber during the inter-eruptive periods. Such evidence demonstrates that the near-real time analysis of strainmeter records is remarkable for its ability to record small transients and highlight recharging phases preceding eruptive activity, which would go undetected with other current methodologies. Under these conditions, the ability to simulate inter-eruptive periods offers an opportunity to estimate the magma recharge rate with important implications for volcano hazard assessment.
埃特纳火山的高精度钻孔应变仪揭示了2017年爆发-溢流活动之前和伴随过程中前所未有的超小应变变化（约10-10）。GPS测量未检测到喷发前或喷发时的变形，由于其精度有限（毫米到几厘米），GPS测量常常无法检测到由短期小型火山事件引起的地面变形。通过对原始数据进行滤波分析并检测到超小应变变化（几十纳应变），发现其与喷发活动存在显著的时间对应关系。首次检测到喷发事件开始前出现的周期性快速指数应变变化，时间尺度约为2-7天。这些变化归因于浅层岩浆库的扩张，在喷发间歇期，浅层岩浆库会从深部补充新的岩浆。根据岩浆的周期性流入和流出导致岩浆房增压/减压来解释应变变化，有助于对岩浆补给量率施加一些限制。已开发出一个有限元模型，采用动力学方法模拟球状岩浆源再增压产生的应变变化的时间演化。估计在喷发间歇期，一个浅层垂直拉长的岩浆房内累计的平均总质量预算约为1-2×10千克，这在喷发质量范围内。这些证据表明，应变仪记录的近实时分析在记录小的瞬变以及突出喷发活动前的补给阶段方面具有显著能力，而其他现有方法无法检测到这些阶段。在这种情况下，模拟喷发间歇期的能力为估计岩浆补给率提供了机会，这对火山灾害评估具有重要意义。
