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首页> 外文期刊>Bulletin of earthquake engineering >Tomography of crustal seismic attenuation in Metropolitan France: implications for seismicity analysis
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Tomography of crustal seismic attenuation in Metropolitan France: implications for seismicity analysis

机译：法国大都市地壳地震衰减的断层扫描：对地震性分析的影响

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In this work, we map the absorption properties of the French crust by analyzing the decay properties of coda waves. Estimation of the coda quality factor $$Q_{c}$$ Q c in five non-overlapping frequency-bands between 1 and 32 Hz is performed for more than 12,000 high-quality seismograms from about 1700 weak to moderate crustal earthquakes recorded between 1995 and 2013. Based on sensitivity analysis, $$Q_{c}$$ Q c is subsequently approximated as an integral of the intrinsic shear wave quality factor $$Q_{i}$$ Q i along the ray connecting the source to the station. After discretization of the medium on a 2-D Cartesian grid, this yields a linear inverse problem for the spatial distribution of $$Q_{i}$$ Q i . The solution is approximated by redistributing $$Q_{c}$$ Q c in the pixels connecting the source to the station and averaging over all paths. This simple procedure allows to obtain frequency-dependent maps of apparent absorption that show lateral variations of $$50%$$ 50 % at length scales ranging from 50 km to 150 km, in all the frequency bands analyzed. At low frequency, the small-scale geological features of the crust are clearly delineated: the Meso-Cenozoic basins (Aquitaine, Brabant, Southeast) appear as strong absorption regions, while crystalline massifs (Armorican, Central Massif, Alps) appear as low absorption zones. At high frequency, the correlation between the surface geological features and the absorption map disappears, except for the deepest Meso-Cenozoic basins which exhibit a strong absorption signature. Based on the tomographic results, we explore the implications of lateral variations of absorption for the analysis of both instrumental and historical seismicity. The main conclusions are as follows: (1) current local magnitude $$M_{L}$$ M L can be over(resp. under)-estimated when absorption is weaker(resp. stronger) than the nominal value assumed in the amplitude-distance relation; (2) both the forward prediction of the earthquake macroseismic i
机译：在这项工作中，我们通过分析尾波的衰减特性，绘制了法国地壳的吸收特性图。对1995年至2013年间记录的约1700次弱至中等地壳地震中的12000多个高质量地震记录，在1至32 Hz之间的五个非重叠频带中，对尾波质量因子$$Q_{c}$$Q c进行了估算。基于灵敏度分析，$$Q_{c}$$Q c随后被近似为沿着连接震源和台站的射线的固有剪切波质量因子$$Q_{i}$$Q i的积分。在二维笛卡尔网格上离散介质后，这将产生$$Qu{i}$$Q i空间分布的线性反问题。该解决方案通过在连接源和站的像素中重新分配$$Q_{c}$$Q c，并在所有路径上求平均值来近似。这个简单的程序可以获得表观吸收的频率依赖图，在分析的所有频带中，在50 km到150 km的长度范围内，显示$$50%$$50%的横向变化。在低频率下，地壳的小规模地质特征被清晰地描绘出来：中新生代盆地（阿基坦、布拉班特、东南部）显示为强吸收区，而结晶地块（Armorican、中央地块、阿尔卑斯）显示为低吸收区。在高频下，地表地质特征与吸收图之间的相关性消失，但最深的中新生代盆地除外，这些盆地表现出强烈的吸收特征。基于层析成像结果，我们探讨了吸收横向变化对仪器地震活动和历史地震活动分析的影响。主要结论如下：（1）当吸收比振幅-距离关系中假设的标称值弱（或强）时，当前的局部震级$$M_{L}$$M L可能超过（或低于）估计值；（2） 地震强震的正演预报

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