Activity of eastern part of the Maniao-Puqian fault in northern Hainan Island and its evaluation of crustal stability

The Maniao-Puqian fault trending east-west, as the major one controlling the Qiongshan earthquake registered 7.5 magnitude on Richter scale in 1605, is a major active fault in the northern Hainan area. Hence, its activity's measuring is critical for crustal stability evaluation and for geological hazard forecast in the northern part of Hainan Island. Various methods were used to determine the distribution of the eastern part of this fault, including remote sensing images interpretation, fault landform mapping, high-density electrical detecting and cross-section drilling validation. The results show that it is spatially composed of 8 north-dipping or south-dipping NEE-trending normal faults (F2-1~F2-8), constituting the three-graben and two-barrier structure, and inheriting the multi-stage activities from the faults before the Pliocene. Five Holocene active faults (F_2-1, F_2-4, F_2-6, F_2-7 and F_2-8), two pre-Quaternary faults (F_2-2 and F_2-5) and one early Miocene fault (F_2-3) were identified by chronological tests. Moreover, the vertical movement rate of F_2-1, F_2-7 and F_2-8 was 0.43-1.79 mm/a, while that of F_2-4 and F_2-6 between 0.12-0.33 mm/a since Holocene. The above research shows that the structures in this area are all in an active state, which has a great influence on the future engineering construction, and the monitoring efforts must be strengthened.