1. Introduction
Haikou Jiangdong New District is the key pioneer district for the construction of China (Hainan) Pilot Free Trade Zone (Figure 1). The 7.5-magnitude Qiongbei earthquake occurred in this area since the Late Quaternary, causing the subsidence and extinction of nearly 72 villages in the epicentral area. Large-scale active fault exploration had never been carried out in the area. In order to ensure the scientific planning of Jiangdong New District, the safe and efficient utilization and management of underground space, and the construction of "transparent Jiangdong" and "intelligent Jiangdong", it is necessary to find out the buried faultsa, and provide the basis for carrying out seismicearthquake risk assessment in the area.
Figure 1: Location of Haikou Jiangdong New DistrictArea
2. Exploration equipment
The shallow P-wave seismic reflection method and gang drill technology were used for exploration. Aries digital seismograph (Figure 2) was used for seismic exploration, which uses 60Hz three-combination series geophones for geophone array, and two KZ-28 vibroseis as the source (Figure 3). Small spacing and multi-point were used for gang drill.
(a) Seismic instrument host (b) Data acquisition station (c) Data transmission cable
Figure 2: Arise telemetry digital seismograph made in Canada
Figure 3: KZ-28 Vibroseis excitation system
3. Work situation
A total of 31 seismic lines with a total length of 139 km and a total of 12,292 physical points have been completed for shallow seismic exploration in this project (Figure 4). There were 79 gang drills and 9 drilling joint profiles (Figure 5). The work area is located in the east coast of Haikou, the east bank area of Nandu River. It is limited by Dongzhai Harbor (the administrative boundary of Haikou) in the east, Nandu River in the west, east coastline in the north, and Ring Expressway Phase II and Provincial Highway 212 in the south, with a total area of about 298 km2.
Figure 4: Schematic diagram of survey line layout
4. Achieved Accomplishment
In this project, the buried fault structure and stratum development in Jiangdong New Area are found out by shallow seismic exploration technology and gang drill construction technology. The results have been verified by field trench exploration, and the effect is good (Figure 6), which provides a strong guarantee for active fault exploration and seismic risk assessment in Jiangdong New Area.
Figure 6: Development of Active Faults Exposed by Exploratory Trench
5. FAQ
Q1: What work does Xi’an Institute mainly carry out in active fault exploration?
A: In terms of active fault exploration, Xi’an Institute mainly carries out 2D/3D P/S-wave reflection method, refraction wave method, microseismic monitoring, etc. The exploration depth spans from several meters to tens of kilometers, and the working area covers lands and waters.
Q2: What is the exploration effect obtained in this area?
A: According to the construction difficulties in this area, targeted measures are taken during the construction, and good exploration results were obtained. The location, occurrence and buried depth of upper breakpoint of the main buried active faults in this area were found out. The exploration results are verified by gang drill and trench excavation, which shows that the seismic exploration has strong pertinence and good exploration effect, and provides a reliable guarantee for active fault exploration and seismic risk assessment in Jiangdong New Area.
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