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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Complex seismic sources in volcanic environments: Radiation modelling and moment tensor inversions
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Complex seismic sources in volcanic environments: Radiation modelling and moment tensor inversions

机译：火山环境中的复杂地震源：辐射建模和矩张量反演

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Long period (LP) signals are special seismic events observed at volcanoes, which comprise both a high frequency onset due to brittle failure and a more energetic low frequency part due to resonance in a fluid-filled conduit. They are critical for volcano monitoring since they can be used as a volcanic forecasting tool. Classic seismology assumes planar faults for seismic sources; however, there is increasing evidence that suggests different fault shapes such as dyke faults and ring faults. We consider in this study narrow dykes and conduits rather than large calderas, hence, we model these complex sources by superposing vertical single double couple (DC) sources arranged along narrow fault structures with inner upward movement. We calculate seismic radiation patterns and synthetic seismograms for a rupture along a dyke, three different partial ring ruptures and a full-ring rupture. Results show that planar faults are the most effective at radiating energy. The more the source geometry deviates from a planar fault the smaller become the amplitudes and therefore the Moment Magnitudes. For example, the amplitudes decrease to 2.4% of the planar radiation for a full-ring rupture and to 0.7% for a dyke rupture. The waveforms produced by partial ring ruptures are in accordance to what is expected in the far field, representing the derivative of the source displacement and emulating radiation of a DC with different azimuths; however, the dyke and full-ring sources produce waveforms that appear to represent the second derivative of the source displacement and negative first onset polarisations. Moment Tensor Inversions support similarities between DC ruptures and partial ring ruptures; however, they show ambiguous solutions for the other sources. This point source assumption can lead to misinterpretations of slip history on the fault and a consistent underestimation of magnitudes which has direct implications for magma ascent estimations derived from seismic amplitudes. (C) 2019 Elsevier B.V. All rights reserved.
机译：长期（LP）信号是在火山中观察到的特殊地震事件，包括因脆性破坏而引起的高频起振和由于充液管道中的共振而引起的高能低频部分。它们对于火山监测至关重要，因为它们可以用作火山预测工具。经典的地震学假设地震源为平面断层。但是，越来越多的证据表明存在不同的断层形状，例如堤坝断层和环形断层。我们在这项研究中考虑的是狭窄的堤坝和管道，而不是大型的火山口，因此，我们通过叠加沿狭窄的断层结构排列的垂直单双耦合（DC）震源并内部向上运动来对这些复杂震源进行建模。我们计算沿堤坝，三个不同的局部环破裂和全环破裂的地震辐射图和合成地震图。结果表明，平面断层在辐射能量方面最有效。源几何形状偏离平面断层的距离越大，振幅就越小，因此矩量就越小。例如，对于全环断裂，振幅减小到平面辐射的2.4％，对于堤坝断裂，减小到0.7％。由部分环破裂产生的波形与远场中预期的一致，表示源位移的导数并模拟具有不同方位角的DC的辐射。但是，堤坝和全环源产生的波形似乎代表了源位移的二阶导数和负的第一起始极化。矩张量反演支持DC破裂和部分环破裂之间的相似性。但是，它们显示了其他来源的模棱两可的解决方案。该点源假设可能导致对断层滑动历史的误解和对幅度的一致低估，这对从地震幅度得出的岩浆上升估计有直接的含义。 （C）2019 Elsevier B.V.保留所有权利。

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