Estimating Cenozoic Thickness in the Beijing Plain Area Using Array Microtremor Data

Online Material: Table of observation radius for microtremor measurements and inverted V S structure. With the rapid expansion of large cities around the world, urban geological surveys provide key information regarding resource development and urban construction. Detailed geological information (e.g., sediment thickness, water table, bedrock structure, rock strength, faults, etc.) is critical to safeguarding large‐structure stability and its operational safety. China’s capital city, Beijing, is one of the largest cities around the world that possesses complex geological structures. Beijing (N39.5°∼41°, E115.5°∼117.5°) is located in the northern area of the Bohai Bay basin, which is surrounded by the Taihang Mountains fold belt to the west, Yanshan fold belt to the north, and Jiliao (Hebei–Liaoning) Rift basin to the southeast (Fig. 1). The structural pattern in the area was formed primarily by the Yanshan tectonic movement, which occurred during the mid‐Jurassic to late Cretaceous. Because of the lack of major tectonic events during the Cenozoic period, the geological structure pattern in the area has remained almost unchanged, as evidenced by the topography seen today (mountainous area in the west and plain area in the east). Numerous major faults exist beneath the Beijing Plain area, acting as the major control factor of the well‐known Beijing Rift Basin (Cai et al. , 2009). The west of the basin is enclosed by the Huangzhuang–Gaoliying fault followed by the Jingxi Uplift, and its east is adjacent to the Nanyuan–Tongxian fault followed by the Daxing Uplift. The resulting structural framework is characterized by two uplifts sandwiching a depression in the center (Jiao and Qiu, 2006; Cai et al. , 2009). The Beijing depression is further divided by smaller northwest–southeast faults, forming smaller structural highs and sags. From the southwest to northeast, there exist the Liangxiang High, Fengtai Sag, Laiguangying High, and Houshayu Sag (see Fig. 1; Luo …