Three‐dimensional P and S wave velocity structure of Redoubt Volcano, Alaska
Three‐dimensional P and S wave velocity structure of Redoubt Volcano, Alaska
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DOI：
10.1029/95jb03046
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发表时间：
1996-04
影响因子：
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通讯作者：
H. Benz;B. Chouet;P. Dawson;J. Lahr;R. Page;J. Hole
中科院分区：
文献类型：
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作者：
H. Benz;B. Chouet;P. Dawson;J. Lahr;R. Page;J. Hole
本文根据阿拉斯加州里道特火山及其周围30个测站的地震台网记录的6219个P波和4008个S波初至时间，确定了该火山及其周围7-8 km地壳的三维P波和S波结构。初至时间的计算使用有限差分技术，它允许灵活的参数化的慢度模型和容易列入地形和源-接收器的几何形状。三维P波速度结构和震源是同时确定的，而三维S波速度模型是使用重新定位的地震活动性和初始S波速度模型从P波速度模型假设平均Vp/Vs比为1.78。收敛是稳定的，在10次迭代后，P波和S波到达时间RMS分别减少约73%和52%。在P波和S波的三维速度模型中观察到的最突出的特征是一个相对低速、近垂直、直径约1公里的管状结构，从海平面以下1公里延伸到6公里。这一特征与地震活动的主体轴向对齐，并被解释为一个高度断裂和蚀变的区域，包括一个岩浆管道。火山北侧深度1至6公里之间的速度结构的特点是横向速度变化大。该区域内的高速度被解释为残余岩脉和岩床，低速度被解释为岩浆迁移的沿着区域。在地壳上部7-8公里处，没有发现暗示岩浆房的大型低速体。
The three-dimensional P and S wave structure of Redoubt Volcano, Alaska, and the underlying crust to depths of 7–8 km is determined from 6219 P wave and 4008 S wave first-arrival times recorded by a 30-station seismograph network deployed on and around the volcano. First-arrival times are calculated using a finite-difference technique, which allows for flexible parameterization of the slowness model and easy inclusion of topography and source-receiver geometry. The three-dimensional P wave velocity structure and hypocenters are determined simultaneously, while the three-dimensional S wave velocity model is determined using the relocated seismicity and an initial S wave velocity model derived from the P wave velocity model assuming an average Vp/Vs ratio of 1.78. Convergence is steady with approximately 73% and 52% reduction in P and S wave arrival time RMS, respectively, after 10 iterations. The most prominent feature observed in the three-dimensional velocity models derived for both P and S waves is a relative low-velocity, near-vertical, pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level. This feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit. The velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations. High velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates. No large low-velocity body suggestive of a magma chamber is resolved in the upper 7–8 km of the crust.