The New Madrid earthquakes : an engineering-geologic interpretation of relict liquefaction features
The New Madrid earthquakes : an engineering-geologic interpretation of relict liquefaction features
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新马德里地震：残余液化特征的工程地质解释
DOI：
10.3133/pp1336b
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发表时间：
1989
影响因子：
1.6
通讯作者：
S. F. Obermeier
中科院分区：
文献类型：
--
作者：
S. F. Obermeier
地震引发的风沙和充满沙子的裂缝出现在从密苏里州查尔斯顿附近向南延伸到阿肯色州标记树以南约20公里的40至60公里宽的地带。地震引起的喷砂和其他液化相关特征的区域几乎只发生在圣弗朗西斯盆地，这是一个冲积低地，通常有一层薄的(2至8米厚)含粘土的顶层，下层约30至60米松散的沙子(底层)。下层砂土的液化使砂土受到冲击。圣弗朗西斯盆地地面上的沙尘和其他与液化有关的特征几乎可以肯定是1811-12年新马德里地震的结果。在这份报告中，冲积层的地质和工程性质与显示液化相关特征边界的地图相结合，大致确定了两次主要地震的震中地带：1811年12月16日的地震和1812年2月7日的地震。分析所用的特性包括下层砂的标准渗透阻力、砂粒的粒度特征、顶层厚度和后第三系冲积层的厚度。分析方法在很大程度上依赖于对砂土液化势的评估。这是通过使用标准渗透试验击数和设计一种方法来实现的，该方法利用液化潜力和地震加速度衰减与震中距离(或者更准确地说，能量释放中心)之间的实际关系的所有可能组合。1811年至1812年的两个能量释放中心与现代小震所定义的地震活动区大体一致。加速度的界限被设置在1811-12年圣弗朗西斯盆地地震产生的沙尘暴的极限。结论表明，顶层厚度、下层砂粒大小和冲积层厚度如何影响圣弗朗西斯盆地的沙尘暴分布。
Earthquake-induced sand blows and sand-filled fissures are present in a belt 40 to 60 km wide that extends from near Charleston, Mo., southward to about 20 km south of Marked Tree, Ark. This region of earthquake-induced sand blows and other liquefaction-related features is almost exclusively in the St. Francis Basin, an alluvial lowland that typically has a thin (2 to 8 m thick), clay-bearing topstratum underlain by about 30 to 60 m of unconsolidated sand (the substratum). Liquefaction of the substratum sands ·has made the sand blows. The sand blows and other liquefaction-related features on the ground surface in the St. Francis Basin are almost certainly results of the New Madrid earthquakes of 1811-12. In this report, geologic and engineering properties of the alluvium are used in combination with a map showing the bounds of the liquefaction-related features to locate approximately the epicentral zones for two of the major shocks: the earthquakes of December 16, 1811, and February 7, 1812. Properties used for the analysis included the Standard Penetration Resistance of the substratum sands, characteristics of the sand's grain size, thickness of the topstratum, and the thickness of the post-Tertiary alluvium. The method of analysis relies largely on the evaluation of the liquefaction potential of the sands. This is done by· using the Standard Penetration Test blow counts and by devising a method that uses all possible combinations of liquefaction potential and a realistic relation between attenuation of earthquake accelerations and distance fr.om the epicenter (or more correctly, energy-release center). Two interpreted 1811-12 energy-release centers generally agree well with zones of seismicity defined by modem, small earthquakes. Bounds on accelerations are placed at the limits of sand blows that were generated by the 1811-12 earthquakes in the St. Francis Basin. Conclusions show how the topstratum thickness, sand size of the substratum, and thickness of alluvium affected the distribution of sand blows in the St. Francis Basin.