A study of structure and activity of the north part of Nankou-Sunhe fault in Beijing

In this paper, three geophysical exploration methods, i.e., controlled source audio-frequency magnetotelluric sounding (CSAMT), shallow seismic and high density resistivity method, were used to establish combined profile for comparison together with drilling engineering and paleomagnetic sample tests, to study the structure and activity of the north part of Nankou-Sunhe fault. The north part of Nankou-Sunhe fault consists of one main fault and one secondary fault. The fault zone is as wide as 400m, exhibiting a step fault extending upwards to the Quaternary strata. Since Quaternary, the activity of fault zone has been remarkable, which reflects the extensional stress environment in the shallow loose layer. According to the accumulated vertical drop of the two plate of the fault in various stages of the Quaternary period, the activity rate of the main fault and its secondary faults were calculated. The main fault in the Early Pleistocene, Middle Pleistocene, Late Pleistocene and Holocene were 0.161mm/a, 0.072mm/a, 0.468mm/a and 0.52mm/a respectively. The secondary fault in the Early Pleistocene, Middle Pleistocene, Late Pleistocene and Holocene were 0.049mm/a, 0.052mm/a, 0.223mm/a and 0.04mm/a respectively.