The Study Of Fault Acitvity And Seismic Hazard In Daihai Fault Zone

Daihai fault zone, as one of the most important fault zones in theBohai-Zhangjiakou-Hetao seismic fracture zone, is located at northeast part of theOrdos block. The previous data about regional active tectonics is limited, andnobody has carried out researches of the paleo-earthquake in the regionsystematically. Moreover, the surrounding areas are the earthquake-prone zones inhistory. In a word, The Daihai fault zone has the possibility of earthquakes, whichdeserves great attention..The contents of this research work includes: scale of the faults, geometry, latestactive time, slip rates, earthquake events, comparison on fault activity withsurrounding regions and the seismic hazard assessment. The results show that:①Daihai fault zone is controlled by two faults, which are Manhan mountainpiedmont fault and Daihai south fault, and strikes~65°. The active time of two faultsis from the late Pleistocene to the Holocene. The activity of faults display a weakertrend from west to east.②With the dating samples of profiles and trenches, this study has found5earthquake events, and their ages are7.51±0.63ka、21.61±1.88ka、53.54±4.81ka、70.27±6.3ka and149.76±16.48ka. Therefore we have unraveled the paleo-earthquakerecurrence interval (15.69ka) and elapsed time (7.51±0.63ka), and the vertical sliprate is0.17-0.28mm/a. We also have found another paleo-earthquake recurrenceinterval through the method of slip rate, which is8.4-13.8ka.④Comparing with the neighboring area, the research region has longerpaleo-earthquake recurrence interval and lower slip rate. It shows that Daihai faultzone is relatively stable. But the zone has the tectonic possibility of earthquakes.Given the earthquakes of Zhang Bei in1998and Helinge’er in1976which occurredin the extended line of Daihai fault zone, the chance of a Ms6earthquake in thefuture is still high.