Abstract: The location of the buried faults, the fault broken layers and the depth of breakpoints in the Tangshan-Hejian-Cixian seismotectonic zone are not clear. We implemented 4 shallow seismic exploration profiles on the Daming Fault, Cangxi Fault, and Dachengdong Fault. Line DZ1 is located on the Daming Fault in the southeast of Daming County. Five breakpoints were dectectd, which are all normal faults, with depths of 95~125m and displacements about 6~12m, offsetting late Pleistocene but not the Holocene. Line DZ2 is located in the east of Xianxian County to dectect the Cangxi Fault. Three breakpoints were detected, all are normal faults, with depths of 170~190m and displacements about 7~10m. The upper breakpoints of the three faults cut the middle Pleistocene. The lines DZ3 and DZ4 are located in the west of Litan Town, Dacheng County. Four breakpoints were detected, with the upper breakpoint depth of 120~130m and displacements about 5~15m. They are all normal faults, and the upper breakpoints of the faults cut the Pleistocene strata.
The result of the exploration of Cixian-Daming Fault is not consistent with the buried depth 1 200m proposed by XU Hua-ming. It is proved that the activity of the fault is also consistent with the overall activity of the Cixian-Daming Fault, which is an active fault since late Pleistocene.
The Dachengdong Fault and Cangxi Fault offset the middle Pleistocene strata. Although the late Pleistocene active faults are generally defined as active faults in the practice of active tectonics research in China, strong earthquakes in eastern China have shorter recurrence period, and earthquakes of magnitude 6 or so may also occur in some middle Pleistocene active faults.
During the compilation of GB18306-2015 “Seismic ground motion parameter zonation map of China”, there were no late Pleistocene active faults in the M6~6.5 potential source areas in eastern China. Therefore, we believe that the Dachengdong and Cangxi faults still have the ability to generate earthquake of magnitude 6 or so, and the faults have some similarities with the seismogenic structures of Xingtai earthquake swarm. Under the action of the latest tectonic stress field, the “deep faults” tearing ruptured successively and expanded upwards, resulting in stress migration and loading between two neighbouring en-echolon concealed faults, so, the Dachengdong and Cangxi faults are the product of this three-dimensional rupture process. The Dachengdong Fault is a “newly-generated” fault resulting from the tearing rupturing and upward expanding of the pre-existing concealed “deept faults” in the middle and lower curst.

Key words: shallow exploration, Tangshan-Hejian-Cixian seismic fault belt, hidden fault

摘要： 由于唐山—河间—磁县地震构造带的位置、 断错层位与上断的埋深尚不明确, 在大名断裂、 沧西断裂、 大城东断裂附近布设了4条浅层地震勘探测线。 测线DZ1位于邯郸市大名县东南部的龙王庙镇, 以探测大名断裂。 在该测线上共探测出5个断点, 均为正断裂, 上断点埋深95~125m, 断距为6~12m, 错断晚更新统而未错断全新统。 DZ2测线位于沧州市献县县城东部, 以探测沧西断裂。 在该测线上共探测出3个断点, 均为正断裂, 上断点埋深170~190m, 断距为7~10m, 断裂上断点切割中更新统。 DZ3和DZ4测线位于大城县里坦镇西, 共探测出4个断点, 上断点埋深120~130m, 断距为5~15m, 均为正断裂, 断裂上断点切割中更新统。 根据探测结果分析认为: 大名断裂是晚更新世活动断裂, 沧西断裂和大城东断裂是中更新世活动断裂, 这3条断裂均有发生6级左右地震的能力。 大城东断裂是先存地壳 “深断裂”向上撕裂状扩展的 “新生断裂”。

关键词: 浅层地震勘探, 唐山-河间-磁县地震构造带, 隐伏断裂