Quaternary Activities Of Northern Segment Of The Shunyi Fault

Shunyi fault is an important Quaternary active fault among NE-trending faults in the north of Beijing plain. Its activity has enormous destruction potential to the development of Beijing. Thus, the relative research on this active fault has great significance.Previous researches have found out that Shunyi fault is a Quaternary synsedimentary fault, and both its hanging wall and footwall accepted sediments during the activity that the sedimentary thicknesses differ a lot between the two walls. Based on previous researches and specific location through comprehensive geophysical prospecting, we obtained data of Quaternary drill in both walls of this fault, conducted comprehensive strata compare on Quaternary strata and discussed the activity routine of Shunyi fault.Integrated analysis of chronological strata, lithology and lithofacies revealed the thickness of strata of different era in hanging wall, Holocene strata of 10 m, middle Pleistocene of 153.3m and the early Pleistocene of 463.9m. The sedimentary facieses transferred from fluvial alluvial facies to limnetic facies and finally to fluvial alluvial facies again, and can be classified into 15 small sedimentary cycles. However, the strata thickness in the footwall were reduced to 9.6m in Holocene strata, 57.5m in late Pleistocene strata, 83.4m in middle Pleistocene and 296.5m in early Pleistocene strata. The sedimentary strata facies also changed from fluvial alluvial facies to limnetic facies and finally to fluvial alluvial facies, and can be classified into 24 small sedimentary cycles.Integrated compare between the hanging wall and footwall also revealed the average activity velocity of Shunyi fault was 0.004mm/a in Holocene, 0.0072mm/a in late Pleistocene, 0.0094mm/a in middle Pleistocen, 0.0054mm/a in early Pleistocene.The activity of Shunyi fault accelerated gradually in early Pleistocene, arrived at the zenith in middle Pleistocene and reduced gradually from late Pleistocene.