Seismic surveys were performed using a novel application of combined active and passive surface wave methods to evaluate the integrity of levees protecting islands in the Sacramento–San Joaquin Delta, California, USA, from flooding. Delta islands have been undergoing rapid subsidence during the past century due to farming practices that have led to the loss of a surficial peat layer. A large earthquake on any one of several active faults in the region could cause multiple levee failures and extensive flooding in the Delta. Surface wave surveys were carried out along the crest of levees using the active method (2D multichannel analysis of surface waves) and along the base of levees using the passive method (microtremor array method). This allowed 2D seismic S‐wave velocity (V_S) profiles to be prepared for each site by combining shallow data from the active survey along the crown of the levee with deeper data from a passive survey along the toe of the levee. TheseV_S profiles reveal a low‐velocity peat layer beneath the levee body that was confirmed by geotechnical borehole logs. Lateral variability of the levee was evaluated using average velocity to the base of the levee versus along‐levee distance.

中文翻译：

---

美国加利福尼亚州萨克拉曼多–圣华金河三角洲的主动和被动地震地表波方法，用于堤坝评估

地震勘探是利用主动和被动表面波组合方法的新颖应用来评估保护美国萨克拉曼多-圣华金河三角洲的岛屿免受洪水侵袭的堤坝的完整性。在过去的一个世纪中，由于耕作方式导致三角洲岛屿的表层泥炭流失，三角洲岛屿一直在迅速沉降。该地区几个活动断层中任何一个断层发生的大地震都可能导致三角洲的多个堤防故障和大面积洪水泛滥。使用主动方法（对表面波进行二维多通道分析）沿着堤坝顶进行表面波调查，并使用被动法（微震阵列方法）沿着堤坝基部进行表面波调查。这允许2D地震S波速度（V _S），通过结合沿堤坝顶部的主动勘测的浅层数据和沿堤坝脚趾的被动勘测的深层数据，为每个站点准备剖面图。这些V _S剖面揭示了堤坝主体下方的低速泥炭层，这一点已通过岩土钻孔测井证实。使用相对于沿堤防距离的堤防基部平均速度来评估堤防的横向变化。