Low-Frequency Hybrid Earthquakes near a Magma Chamber in Afar: Quantifying Path Effects
Low-Frequency Hybrid Earthquakes near a Magma Chamber in Afar: Quantifying Path Effects
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DOI：
10.1785/0120090111
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发表时间：
2010-10-01
影响因子：
3
通讯作者：
Wright, Tim
中科院分区：
文献类型：
--
作者：
Cote, Dustin M.;Belachew, Manahloh;Wright, Tim
活火山活动区含有复杂的速度结构，使震源机制的解释复杂化。我们研究了805个地震的频谱特征，紧接着大量玄武岩岩脉侵入和相关的Dabbahu火山在阿法尔凹陷的近源地震仪记录的侧翼喷发。我们使用这些结果来量化的散射和衰减的贡献，从Dabbahu火山下方和周围的堤防区的低频混合和火山构造地震集群观测到的频谱。我们发现强烈的信号振幅和频率的变化，记录在车站分离的地震少至2公里，所造成的优先衰减的高频率取决于Vantage位置。这些意见意味着，有大的阻抗对比附近的冷却，固化，最近侵入的堤坝。我们估计内在的吸收衰减系数，Q（I），和逆散射长度，g（0），平均超过300平方公里的区域Dabbahu下面。我们的结果与意大利火山区研究的最高衰减系数一致（对于2 Hz的信号，Q（I）（-1）约为0.02，g（0）约为0.1 km（-1））。这两个参数的大小表明，由于最近的岩浆侵入和相关的断裂，该地区存在较大的阻抗对比。
Areas of active volcanism contain elaborate velocity structures that complicate interpretations of earthquake source mechanisms. We examine the spectral characteristics of 805 earthquakes that immediately followed a large volume basaltic dike intrusion and associated silicic flank eruption of Dabbahu volcano in the Afar Depression as recorded on near-source seismometers. We use these results to quantify the contribution of scattering and attenuation to the observed spectra of low-frequency hybrid and volcano-tectonic earthquake clusters from beneath Dabbahu volcano and around the dike zone. We find strong variations in the signal amplitude and frequency content of earthquakes recorded at stations separated by as little as 2 km, caused by preferential attenuation of high frequencies depending on the vantage point. These observations imply that there are large impedance contrasts near the cooling, solidifying, and recently intruded dike. We estimate the intrinsic absorption attenuation coefficient, Q(I), and inverse scattering length, g(0), averaged over a 300-sq-km area beneath Dabbahu. Our results are consistent with the highest attenuation coefficients from studies of volcanic provinces in Italy (Q(I)(-1)approximate to 0.02, g(0)approximate to 0.1 km(-1) for a signal at 2 Hz). The magnitude of these two parameters indicates there are large impedance contrasts present in the area due to the recent intrusion of magma and associated fracturing.