Preliminary analysis of the influence of the activity in the Yalu River fault zone on the Wulongbei geothermal hot springs in Dandong under the action of crustal stress

Abstract

The Yalu River fault zone is an essential branch of the Tanlu fault system with intense present-day tectonic activity. Over 60 hot springs are exposed along the fault zone with abundant geothermal resources. In order to find out the present-day crustal stress state and fault activity in the Wulongbei area of the southern section of the fault zone and to study the control and long-term influence of the fault activity on the geothermal water bodies of hot springs, in-situ stress measurements of 12 sections were carried out in the area by hydraulic fracturing method. The results showed that the maximum and minimum horizontal principal stresses (SH and Sh) range from 6.00 to 13.52 MPa and 3.18 to 7.26 MPa, respectively, in the depth range of 36.80–215.50 meters. In general, the three principal stresses showed an increasing trend with depth; in the middle section of the fracture zone (198.60–207.80 m), the three principal stress values meet the relation of SH>Sv>Sh, which is favorable to the strike-slip activity and has some potential for water-rich hydraulic conductivity, while the three principal stress values of the upper section (36.80–196.63 m) and lower section (215.50 m) accord with SH>Sh>Sv, which is favorable to the reverse fault activity, with poor longitudinal continuity of heat flow channels and poor hydraulic conductivity. Based on the present-day relationship between stress field characteristics and fault activity, it is deduced that the decline of the hot spring level in the Wulongbei area may be due to the fault activity under compressive stress, which gradually reduced the space of the hydraulic conductivity system by extrusion, causing the increase of discharge of runoff in other directions and the reduction of hot spring water supply. Based on the Coulomb frictional instability theory, the in-situ stress value in the depth range of 36.80–113.20 m in the fault zone reaches the lower limit of the critical stress value required for its activity. There is a possibility of dislocation in the future, and the fault activity may change the hot spring geothermal water supply channel. The research results have theoretical significance in studying the role of faults in controlling hot spring geothermal water and applying in-situ stress measurements near fault zones in geothermal research.

Keywords

• yalu river fault zone
• in-situ stress measurements by hydraulic fracturing method
• crustal stress state
• geothermal hot spring
• fault activity