Neotectonic Activity Of The Yilan-Yitong Fault

As a main branch of the northern segment of the Tan-Lu Fault Zone, the Yilan-Yitong fault passes through the densely populated area of northeast China where there is a large number of buildings.Study on neotectonic and seismic activities of the Yilan-Yitong Fault, we can not only know the important, strong tectionic zone’s future activity trends, seismic activity regularities and mechanism of geological disasters, but also provide a reference to earthquake prevention, disaster mitigation, evaluation of the crust stability and related construction planning for a region affected by the fault zone. Therefore, this study has important social and economic significance.Based on DEM, remote sensing, gravity and aeromagnetic anomaly plane map data, extension and spatial location of the Yilan-Yitong fault zone are determined in this work.. Seismic and electrical profiles as well as other geophysical data reveal cross-section textures and features of the fault zone. Our detailed field investigation demonstrates that active faults are widely present in the Yilan-Yitong Fault. They are composed of two main NE-striking active faults called the eastern and western active faults respectively and developed along boundary faults of the Paleogene graben. The active faults mainly show the crashed-type texture and reverse dextral slip. Stress inversion from many fault-slip data of the active faults show that Quaternary activity of the faults took place under the E-W compression that transformed into ENE-WSW compression at present. Our field observation and 14C dating, OSL dating, in combination with previous dating results and earthquake distribution, suggest that the most recent periods of activity on the western active fault show alternation of Holocene and late Pleistocene whereas those on the eastern active fault are dominated by early-middle Pleistocene. The active faults in the Yilan-Yitong Fault present differential activities that show more intense activity on the western fault than on the eastern one, younger activity on the western fault, alternation of intense and weak activity, change in the most recent periods of activity along their strike as well as inhomogeneous distribution of earthquakes. Segmentation and differential activities of the faults along their strike mainly result from cutting of NW-striking faults on them.