1. Introduction
There are three large regional faults in Huai’an City, Jiangsu Province, including Huaiyin-Xiangshuikou fault, Wuxi-Suqian fault and Hongze-Goudun fault. At present, there are few researches on the development characteristics, occurrence location and activity of these faults, so it is impossible to scientifically identify their latest active times and evaluate their seismic risk and harmfulness.
2. Treatment solution
The shallow seismic exploration by P-wave reflection method was adopted. 9 shallow seismic exploration lines were arranged at the locations where the three main faults may pass through (Figure 1). Aries digital seismograph (Figure 2) and 60Hz triple combination series geophones were used for exploration and two SM-26 vibrator vehicle were used for excitation (Figure 3).
Figure 3: Schematic diagram of the location of the shallow seismic survey lines in Huai'an City
(a) Seismic instrument host (b) Data acquisition station (c) Data transmission cable
Figure 2: Arise telemetry digital seismograph made in Canada
Figure 3: Vibrator vehicle
3. Work situation
In this shallow seismic exploration, a total of 9 seismic survey lines were surveyed, with the total length of 60.4km and the total of 3,379 physical points. The coordinates of the work area are (33°42′, 118°58′, 33°40′, 119°15′, 33°27′, 119°12′, 33°22′, 119°04′, 33°16′, 119°00′, 33°16′, 118°48′), covering the downtown and western suburbs of Huai’an City, with an area of about 1,211km2.
4. Achieved accomplishment
This controlled shallow seismic exploration of the active fault and seismic risk assessment in Huai'an City has found out the fault activity characteristics, shallow and deep tectonic characteristics, buried depth and strike position of the upper breakpoint of Huaiyin-Xiangshui fault, Wuxi-Suqian fault and Hongze-Goudun fault, as well as the relationship between the deep buried old faults and the main faults of each seismic line in the area.
Figure 4: Interpretation of the seismic time profile along line L1-1
5. FAQ
Q1: Why don’t use other methods to explore the location and characteristics of buried faults?
A: Seismic exploration by P-wave reflection multiple covering is the most effective and direct method for exploring buried faults, which has a good effect on dividing sedimentary stratigraphic sequences with a certain thickness, exploring geological structures such as buried active faults, suppressing interference and improving SNR of seismic data by using multiple covering technology.
Q2: What does your company mainly do in this respect?
A: For shallow seismic exploration of active faults, CCTEG Xi’an Research Institute has successfully completed the design, field acquisition and indoor seismic data processing and interpretation.
Q3: What advantages does CCTEG Xi’an Research Institute have in this field compared with other companies?
A: CCTEG Xi’an Research Institute has successfully completed many shallow seismic exploration projects held by the seismological bureaus and other institutions in many provinces and cities across the country since it stepped into the seismic active fault exploration. In addition to a considerable number of advanced software and hardware for seismic exploration acquisition, processing and interpretation, it also has a complete set of quality and safety management systems for such projects.
Q4: What is the cost of shallow seismic exploration?
A: The cost of this kind of work is mainly subject to regional differences, terrain differences, geological task difficulties, safety and other factors. The costs of different project have certain differences and cannot be generalized.
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