This paper presents an application of geophysical techniques to determine the liquefaction potential of the surface sand layer under wave loading in an atoll island, Magoodhoo Island (Faafu Atoll). Measurements of background noise (H/V technique), seismic refraction profiles (tomography), surface wave inversion and electrical resistivity tomography were applied to study the properties of the substratum. Geotechnical analysis provided the relative soil density (Dr = 55%) and the grading curves; the comparison of these parameters with geophysical data, allowed to identify indicative features related to ground liquefaction phenomena. Microtremor measurements calculated a fundamental site resonance in the frequency range of 1.42–23.19 Hz. Velocity profiles showed that bedrock interface depth varies from approximately z = 35 m north-east of the island, to z = 25 m south-west, while in the most north-eastern external area, it was not detected. These results suggested a significant lateral variability of the site seismic response throughout the study area. Liquefaction triggering with wave heights varying between 2.0 and 3.0 m and 70–300 cycles was calculated. Also, considering an average wave period of 6 s, liquefaction was more likely after 7–30 min. The soil vulnerability index K_g was also used to evaluate the soil liquefaction hazard suggesting that the north-eastern island sector is more susceptible to liquefaction, confirmed also by the building damage status as compared to other areas of the island. The results obtained in the survey highlight that in an atoll island, where potential disasters can be caused by several natural causes, saturated loose sands lose their strength and stiffness if subjected to wave loading.

中文翻译：

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研究潜在海浪引起的液化的地球物理方法：以马古德霍岛为例（法阿富环礁，马尔代夫，印度洋）

本文介绍了地球物理技术在确定波浪岛下的玛古德霍岛（法古夫环礁）的波浪载荷下地表砂层液化潜力的应用。测量背景噪声（H / V技术），地震折射剖面（断层扫描），表面波反演和电阻率层析成像，以研究地下层的特性。岩土分析提供了相对土壤密度（Dr = 55％）和等级曲线；这些参数与地球物理数据的比较，可以确定与地面液化现象有关的指示性特征。微小震颤的测量计算出在1.42–23.19 Hz频率范围内的基本位点共振。速度剖面表明，基岩界面深度在该岛东北约z = 35 m处变化，到z =西南25 m，而在最东北的外部区域中，未检测到。这些结果表明，整个研究区域的现场地震响应存在明显的横向变化。计算了波高在2.0到3.0 m和70-300个周期之间变化的液化触发。另外，考虑到平均波浪周期为6 s，在7–30分钟后更可能发生液化。土壤脆弱性指数K_g还用于评估土壤液化危险，表明东北岛屿地区更容易液化，并且与该岛屿其他地区相比，建筑物的破坏状况也证实了这一点。调查结果表明，在一个环礁岛上，自然灾害可能是由多种自然原因引起的，饱和的松散沙子在承受波浪载荷时会失去强度和刚度。