Response Characteristics Of Daihai Lake Sediments To Earthquake And Reconstruction Of Its Sedimentary Sequence

Lacustrine deposits are highly sensitive to changes in their sedimentary environment and can't not be easily disturbed.Their sedimentary sequence can continuously record rich sedimentary environmental information and tectonic events,and may record continuous and complete active tectonic records,providing a new perspective for the study of historical earthquakes.The study area in this paper is Daihai Lake in Inner Mongolia,which is a typical inland closed faulted lake basin.It is located at the junction of Yinshan fault block,Ordos fault block and Taihang fault block in the northwestern part of the North China Platform.There have been many earthquakes around it.We performed CT scan,XRF experiment,and laser particle size experiment on short core samples(80cm,70cm)drilled by gravity at two different locations in Daihai Lake.Observing the bedding features of the deposit without cutting the core by CT scanning.Using XRF experiments to obtain deposition curves of some deposited elements and magnetic susceptibility.The particle size curve is used to obtain the sedimentation sorting and the change of the sedimentation content of each level of particle size.By comparing with the sedimentary index curve selected by the previous study of Daihai,we select appropriate sedimentary dating data and establish the corresponding depth-chronological relationship.Comparing the known earthquake occurrence sequence in the study area with the chronological framework and the deposition curve of various experimental indicators,the inversion of the sedimentary environment changes within about 70 cm of the Daihai surface and the response characteristics of earthquakes in the study area have mainly obtained the following results:(1)Through the comparison of experimental indicators,it is found that the indicators of Si,Fe,K,Ti,Al,Mn and other indicators that indicate the influx of exogenous substances in the lake core indicators have a strong positive correlation and an inverse correlation with the Cl element curve,which can be better reflected The source and influx of foreign matter peaks and changes in the depositional environment.(2)Through the comparison of the characteristics of the sedimentation curves of various indicators,the occurrence of the two cores indicates that there have been two large-scale rapid deposition events and several small-scale emergencies within the core sampling depth.And due to the topographic factors and rapid deposition of the lake bottom The different degree of influence caused the average deposition rate at sampling point 1 to be too large.(3)Combining relevant data such as local logs,verifying the abnormal fluctuations in the sedimentation curve and finding that the first large-scale fluctuations and the second and other small-scale fluctuations have obvious differences in the grain size curve,which is speculated to be the large coastal area of Daihai Lake Large-scale construction of power plants resulted.The second and several small-scale fluctuations all have a good corresponding relationship with the earthquake sequence that occurred in the Daihai Basin.(4)In the analysis of lacustrine sedimentation,various indicators have different response characteristics to different sedimentary environments.According to the experimental data in this article,we summarize the different sedimentary characteristics and laws of sedimentary indexes in the Daihai area under the influence of earthquakes or human activities,and provide a criterion for the discovery of earthquakes that have not been recorded in historical data.At the same time,for the selected representative indicators,multiple indicators should be selected for combined analysis.For example,in the experiments in this article,the grain size characteristics of the sediments and the magnetic susceptibility and other characteristics are significantly different at a sudden change,indicating that they affect the deposition factors Is obviously different.