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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >P wave crustal velocity structure in the greater Mount Rainier area from local earthquake tomography
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P wave crustal velocity structure in the greater Mount Rainier area from local earthquake tomography

机译：从局部地震层析成像看大雷尼尔山地区的P波地壳速度结构

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We present results from a local earthquake tomographic imaging experiment in the greater Mount Rainier area. We inverted P wave arrival times from local earthquakes recorded at permanent and temporary Pacific Northwest Seismograph Network seismographs between 1980 and 1996. We used a method similar to that described by Lees and Crosson [1989], modified to incorporate the parameter separation method for decoupling the hypocenter and velocity problems. In the upper 7 km of the resulting model there is good correlation between velocity anomalies and surface geology. Many focal mechanisms within the St. Helens seismic zone have nodal planes parallel to the epicentral trend as well as to a north-south trending low-velocity trough, leading us to speculate that the trough represents a zone of structural weakness in which a moderate (M 6.5-7.0) earthquake could occur. In contrast, the western Rainier seismic zone does not correlate in any simple way with anomaly patterns or focal mechanism fault planes, leading us to infer that it is less likely to experience a moderate earthquake. A approx 10 km-wide low-velocity anomaly occurs 5 to 18 km beneath the summit of Mount Rainier, which we interpret to be a signal of a region composed of hot, fractured rock with possible small amounts of melt or fluid. No systematic velocity pattern is observed in association with the southern Washington Cascades conductor. A midcrustal anomaly parallels the Olympic-Wallowa lineament as well as several other geophysical trends, indicating that it may play an important role in regional tectonics.
机译：我们介绍了来自更大的雷尼尔山地区的局部地震层析成像实验的结果。我们将1980年至1996年期间在太平洋西北地震台网永久和临时地震台录得的本地地震的P波到达时间进行了倒转。我们使用了类似于Lees和Crosson [1989]所描述的方法，并修改了参数分离方法以将地震波解耦。震源和速度问题。在所得模型的上部7 km中，速度异常与地表地质之间具有良好的相关性。圣海伦斯地震带内的许多震源机制具有平行于震中趋势以及南北向低速波谷的节面，这使我们推测波谷代表了结构性弱化带，其中中等强度（可能会发生6.5-7.0级M级地震。相反，西部的雷尼尔地震带与异常模式或震源机制断层平面没有任何简单的关联，这使我们推断该地震发生中度地震的可能性较小。在雷尼尔山山顶下方5至18公里处，发生了大约10公里宽的低速异常，我们将其解释为一个信号，该区域由热的，破裂的岩石组成，可能含有少量的熔体或流体。没有观察到与南部华盛顿小瀑布指挥家有关的系统速度模式。中地壳异常与奥林匹克-沃洛纳系以及其他一些地球物理趋势相似，表明它可能在区域构造中起重要作用。

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