Researches on activities of main faults in Lianyungang City

Geological and geomorphological survey, high accuracy shallow seismic P-wave reflection and refraction exploration and S-wave exploration, borehole joint geological section drilling across fault, and age dating technologies were applied for the surveying on active fault in Lianyungang City, Jiangsu, East China. Nine main faults were prospected. The Quaternary activities of three typical faults including the Haizhou-hanshan Fault (F₁) were studied with the first hand documents in high quality obtained in this project. Results show that the NNE-trending F₁ and the NE-trending Shaoxianghe Fault (F₃) are probably the early Quaternary faults, while the NW-trending Nancheng-xinpu Fault (F₈) and other main faults are all pre-Quaternary faults. Lianyungang City situates on the Quaternary weakly active tectonic zone in the eastern part of China, and it shares similar seismo-tectonic background with the Shandong Peninsula to the north. Both the Quaternary fault activity and the seismicity are weak. In history, only one destructive earthquake was recorded in the city area, i.e. the 1495 Haizhou M4¾ earthquake. Epicenters of earthquakes with magnitude ≥6 concentrated in peripheral regions, namely, along the NNE-trending Tanlu Fault Zone, the NW-trending Bohai-Weihai Fault Zone, and in the northern depression and the southern depression of the south Yellow Sea. The potential earthquake outbreaks with M5±0.5 in future in Lianyungang City are possible judging from the structural analogy principle. However, the influences of strong earthquakes on the study area from adjacent Tanlu Fault Zone and the northern or southern depression of the south Yellow Sea could overtake the local geological forces thus cannot be neglected. For example, the 1668 Tancheng M8½ earthquake at the Tanlu Fault Zone reached Intensity Ⅷ in the Lianyungang area. Thus, risks of both local earthquakes with M5±0.5 and strong earthquakes from surrounding areas should be considered with great concern with effective prevention and disaster reduction measurement of Lianyungang City.