1. Introduction
Hongge Planning District is located in Hongge Town, Yanbian County, Panzhihua City, a nation-level characteristic town and a key town in the southeast of the city. It is situated in Panxi-Central Yunnan medium uplift area with an uplift range of about 1,000-2,000m since Quaternary. The large-scale Xigeda Fault developed in the area is mainly characterized by sinistral shear movement, which caused Yutai M6.75 earthquake in 1955 and Panzhihua M6.1 earthquake on August 30, 2008. Therefore, the fault has great influence on the further planning and development of Hongge Planning District, but the exploration and understanding of the fault are not enough, and it is urgent to find out the distribution position and activity characteristics of the fault in the area.
2. Treatment solution
7 shallow seismic exploration lines (Figure 1) were arranged in the district by using P-wave reflection method to find out the spatial distribution position and characteristics of Xigeda fault and to accurately determine the position by gang drill. For seismic exploration, Aries digital seismograph (Figure 2) and 60Hz three-combination series geophone were used, which were excited by explosives and detonators and the holes were drilled by portable mountainous drill rig (Figure 3).
Figure 1: Schematic diagram of the scope of Hongge Planning District and the proposed seismic survey lines
(a) Seismic instrument host (b) Data acquisition station (c) Data transmission cable
Figure 2: Arise telemetry digital seismograph made in Canada
Figure 3: Site work of portable mountainous drill rig
3. Work situation
A total of 7 seismic survey lines were arranged in shallow seismic exploration, with a total length of 6.2km and a total of 523 physical points. A total of 13 boreholes, with a total footage of 811m, were used to accurately verify the position of Xigeda Fault. The working area is located between E 101°55.6′-101°56.7′ and N 26°30.5′-26°34.2′, with an area of about 16km2.
4. Achieved accomplishment
The shallow seismic exploration and geological drilling project in Hongge Planning District identified the occurrence characteristics, buried depth of the upper and the lower breakpoints and their vertical projection positions of Xigeda Fault on the surface and other branch faults, and determined their active times.
Figure 4: Seismic time profile of migration of line C1
Figure 5: Engineering geological section of line C1
5. FAQ
Q1: Why didn’t we use other methods to explore the location and characteristics of the buried faults?
A: Seismic exploration by P-wave reflection multiple covering is the most effective and direct method for exploring buried faults, has good effect for dividing sedimentary stratigraphic sequences with certain thickness, exploring geological structures such as buried active faults, suppressing interference and improving SNR of seismic data by using multiple covering technology. The combination of shallow seismic exploration and gang drill verification can better expose the upper and the lower breakpoints of the buried faults.
Q2: What does your company mainly do in this respect?
A: In view of shallow seismic exploration of buried faults, Xi’an Research Institute mainly accurately locates the upper breakpoint of buried faults by geophysical prospecting and gang drill verification. In geophysical exploration, the seismic data are mainly acquired on the field, and the seismic data is mainly processed and interpreted indoor. In gang drill, field geological drilling and core logging are mainly carried out, while drilling and analysis of the upper and the lower breakpoints are mainly carried out indoors, and interpretation maps of cross-hole section are prepared
Q3: What advantages does Xi’an Research Institute have in this field compared with other companies?
A: Xi’an Institute has successfully completed many shallow seismic exploration projects of the seismological bureaus and other institutions in many provinces and cities across the country since it stepped into the seismic exploration of the active faults. 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. It also has accumulated certain work achievements and experiences in the breakpoint drilling and accurate verification of the faults.
Q4: What is the cost of shallow seismic exploration and gang drill?
A: The cost of this kind of work is mainly subject to regional differences, terrain differences, geological task difficulties, environmental protection, safety and other factors. The costs of different projects have certain differences and cannot be generalized.
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