关键词: 变形带, 浅层地震, 断层气, 钻孔联合剖面

Abstract:

Active fault deformation zones are commonly referred to as fault failure zones. The width of the deformation zone is generally several meters to tens of meters, representing the strongest range of fault activity deformation and the degree of exposure of future surface fracture zones, that is, the severely damaged strip area, which is a key avoidance object for construction projects.
Modern ground buildings(structures)generally have underground engineering that requires excavation of foundations ranging from a few meters to several tens of meters. Hidden faults that cannot be exposed by foundation excavation and whose buried depth is less than 60m may also form fractures on the surface, but the location of the fractures is difficult to determine. At the same time, the long-term creep of the hidden faults and the historical multiple periods of seismicity have formed significant plastic deformation or weak displacement areas near the surface. Therefore, studying the range of hidden fault deformation zones of Quaternary sedimentary layers can provide scientific basis for scientific avoidance of active faults.
The local changes of the Fenhe River channel(surface deformation survey)reflect the stages and stages of tectonic activity in the Taiyuan Basin, mainly including the early stage of the third episode of the Xishan Mountains, the Huangkun movement, and the Gonghe movement, and there are adjustments in two modes of movement: strike slip and tension; Through the precise processing and interpretation of 15 shallow seismic survey lines, and combined with some geological deep hole profiles, the stratigraphic age of the seismic stratigraphic profile was marked, revealing the multi-stage expansion activity of the Tianzhuang fault inverted terrace, and further demonstrating the correctness of the basin's third-phase expansion activity revealed by the changes in the Fenhe River channel.
The Qinghai-Tibetan movement(3.4~1.66Ma BP)in the third episode of Xishan formed the front edge of Tianzhuang fault in Pliocene and the strike slip compression tectonic activity before the Qinghai-Tibetan movement formed the rear edge section. The Huangkun movement(1.2~0.7Ma BP)formed the front edge section of Tianzhuang fault in Middle Early Pleistocene Late Early Pleistocene and the tectonic activity between Qinghai-Tibetan and Huangkun movement formed the rear edge section of Middle Early Pleistocene, The Gonghe movement(after 0.15Ma)formed the front section of the Tianzhuang fault F_2-Qh(creep slip)and the rear section of the Tianzhuang Fault $\mathbb{F}_{1-\mathbb{Q}_{\mathbb{P}}^3} $ in the middle Pleistocene uplift tectonic activity. The section formed by the Qinghai-Tibetan movement was the oldest, the section formed by the Huangkun movement was the second, and the section formed by the Gonghe movement was the latest. The dislocation activity of the section formed by the Gonghe movement occurred in the middle Pleistocene and Late Pleistocene, and the Holocene was dominated by slow seismicity, Shown as weak creep movement, the front edge section of the Tianzhuang Fault F_2-Qh(creep)and the rear edge section of $\mathbb{F}_{1-\mathbb{Q}_{\mathbb{P}}^3} $ are active sections that require attention in urban planning.
In the structural history of the Tianzhuang fault, as a branch of Jiaocheng fault in the NEE direction, together with Jiaocheng fault, controlled the sedimentary process of the basin before the middle Pleistocene in the Qingxu sag. Through this work, the response of the Tianzhuang fault to the Qinghai-Tibetan movement, the Huangkun movement, and the Communist movement has been systematically revealed. Finally, it is considered that the evaluation of the deformation zone formed by the Tianzhuang fault since the latest Gonghe movement(Late Pleistocene)is of practical significance for engineering earthquake resistance and avoiding faults. Through the measurement of fault gas profiles and evaluation of fault gas anomaly zones of the Cross Tianzhuang Fault in Xizancun and Malianying Road, combined with the detailed stratigraphic faulting revealed by the joint drilling profiles of the Cross Tianzhuang Fault in Xizancun and Malianying Road, the extension of the main active section F_2-Qh on both sides of the front edge of the Tianzhuang Fault since the Republican Movement has been determined to be 30m, which is the deformation zone range. The extension of the main active section on both sides of the rear edge of the Tianzhuang Fault is 55m, which is the deformation zone range, Considering the specific needs of engineering seismic fortification, it is advisable to conduct seismic fortification and engineering design based on the deformation zone range on both sides of these two main sections.

Key words: Deformation zone, Shallow earthquake, Fault gas, Borehole joint section