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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Crustal attenuation and site effects at Parkfield, California
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Crustal attenuation and site effects at Parkfield, California

机译：加利福尼亚帕克菲尔德的地壳衰减和场地效应

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At Parkfield, California, the San Andreas fault separates strongly contrasting rock types: high velocity Salinian granite to the SW and lower velocity Franciscan basement to the NE. I use the recordings of nine earthquakes in 10 boreholes (less than or equal to 1000 m deep) and calculate P and S wave spectral ratios between borehole recordings at different depths to eliminate the source. I then invert for Q on each side of the San Andreas fault. I find that the attenuation on the NE side df the fault (Q(NE)similar to 100) is approximately twice that on the SW side (Q(SW)similar to 200) in the depth range similar to 200 m to 5 km. Q(P) and Q(S) are similar, but their ratio is not well resolved. I estimate Q(P)similar to 50 and Q(S)similar to 80 in the fault zone itself by combining recordings at a site within the fault zone with the inversion results and confirm that it is a low -Q zone. Q is also observed to increase with depth, and the rate of this increase decreases as the depth increases. In the upper 1 km at the Varian well (on the NE side of the San Andreas fault), Q(P)similar to 30 and Q(S)similar to 20, with Q(P) increasing from similar to 20 between 0 and 300 m to similar to 55 between 600 and 900 m. This study demonstrates that the borehole seismometers at Parkfield are not deep enough for the effects of attenuation to be ignored in analysis of small earthquakes. Also, the attenuation below 1 km on the NE side of the fault is actually larger than that below similar to 200 m on the SW side. The results of this study suggest that the attenuation at depths of a few hundred to a few thousand meters should be considered when estimating site effects in seismic hazard studies. [References: 41]
机译：在加利福尼亚州的帕克菲尔德，圣安德烈亚斯断层将强烈对比的岩石类型分开：西南部为高速萨利尼花岗岩，东北部为低速方济各坎基底。我使用了10个钻孔（小于或等于1000 m深）中的9次地震的记录，并计算了不同深度的井下记录之间的P和S波谱比，以消除震源。然后，我在圣安德烈亚斯断层的每一侧求Q。我发现，在深度为200 m至5 km的情况下，断层在NE侧的衰减（Q（NE）类似于100）大约是SW侧的衰减（Q（SW）类似于200）的两倍。 Q（P）和Q（S）相似，但是它们的比率不能很好地解析。通过结合断层带内某个位置的记录和反演结果，我估计断层带本身的Q（P）近似于50，Q（S）类似于80。还观察到Q随深度增加，并且该增加的速率随深度增加而减小。在瓦里安（Varian）井的上部1 km（圣安德烈亚斯断层的NE侧），Q（P）近似于30，Q（S）近似于20，而Q（P）在0到0之间从相似的20增加。 300 m至600和900 m之间的55相似。这项研究表明，帕克菲尔德的钻孔地震仪的深度不足以在小地震分析中忽略衰减的影响。同样，故障NE侧1 km以下的衰减实际上大于SW侧200 m以下的衰减。这项研究的结果表明，在地震危险性研究中估算场地影响时，应考虑数百米至几千米深度处的衰减。 [参考：41]

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