image: (a) Seismic tectonic background and borehole distribution of in situ stress measurements around the Longmenshan thrust belt; the depth of borehole GQX-1 is 1,000 m, and that of borehole GQX-5 is 500 m. (b) Focal mechanism solution of the Longmenshan thrust belt; (c) rose diagram of stress directions. view more
Credit: ©Science China Press
This study is led by Professor Jingshui HUANG (University of Science and Technology of China), and Bing LI，Xiwei XU, Qiliang GUO and Furen XIE ( National Institute of Natural Hazards, Ministry of Emergency Management).
The team has carried out hydraulic fracturing stress measurements in two boreholes near the town of Dachuan in the Dayi seismic gap of the Longmenshan Fault Zone. They find that high stresses still exist in the Dachuan-Shuangshi Fault Zone, indicating that there is still a hazard of strong earthquakes in the Dayi seismic gap.
Whether strong earthquakes will occur in Dayi seismic gap of Longmenshan Fault Zone recently remains hotly debated. Researchers arranged 2 boreholes at a depth of 1000 m and 500 m in 2019 in the upper and lower plates of the Dachuan-Shuangshi Fault, which has a high seismic hazard in the Dayi Seismic Gap. Two hydraulic fracturing stress measurements were carried out in 2019 and 2020. The results indicate that the area around the Dachuan-Shuangshi fault zone is still at high stress state. The three-dimensional velocity structure and ground temperature measurements indicate that the crustal structure above 18km near the borehole is brittle, and the deep rock structure has the conditions of high stress. The strong eastward compression of the seismic gap by the Qinghai-Tibet Plateau will then be transmitted to the north, the east and south ends of the seismic gap, and high stress will still exist in these areas.
Although the depth of stress measurements in the 2 boreholes were less than 1000m, the results combined with the 3D velocity structure and ground temperature measurements suggest that the Dayi seismic gap is still with the capability for moderately strong earthquakes and should be taken seriously.
See the article:
In situ Stress State and Seismic Hazard in the Dayi Seismic Gap of the Longmenshan Thrust Belt, https://link.springer.com/article/10.1007/s11430-021-9915-4
Journal
Science China Earth Sciences