| The paleo-dammed lakes located at the upstream of Minjiang River have beenstudied. A large number of field recording information has been collected andintegrated during field research and ancient earthquake information has beenidentified. This study is focus on the Diexi paleo-dammed lake due to its preservedenvironment. The results have significant contributions to the estimation of ancientearthquake frequencies and duration, as well as the prediction of earthquake in thisregion nowadays. The ancient earthquake has been studied through site survey,drilling sample, in-house test, and physical experiment simulation. The followingresults are obtained:(1)Field survey and drilling sample analysis show that Diexi paleo-dammedlake lacustrine sediments retained a lot of information on geological environment andclimate information. Ten (10) earthquake vestiges are found in the stack of more than240meters of lake lacustrine sediments. These earthquake vestiges exhibitedconvolution structure, flame structure and so on.(2) Ten (10) groups of particle characteristic size are obtained throughparticulate size description analysis from the earthquake vestiges and their lowercontact layers in the paleo-dammed lake lacustrine sediments. The particlecharacteristic size is in the range of0.0000to0.1019mm. Although the particle sizesare similar both in earthquake vestiges and the lower contact layer, earthquakevestiges contain more large size particles and slit.(3) The establishment of the earthquake vestiges in the paleo-dammed lakelacustrine sediments has been simulated through shaking table model tests. Thedisturbance phenomena observed in the tests is consistent with what has been seenfrom the site surveys and drilling samples. The consolidated sediments from previousshaking test are not disturbed again during the next shaking table model test.Therefore, one disturbance is corresponding to one earthquake. According to the agetest information, the (10) earthquake vestiges in the paleo-dammed lake lacustrinesediments are corresponding to ten (10) earthquakes between15KB.P and30KB.P. And the earthquake duration can be determined for Dexi region during this1.5KB.Pconsequently.(4)Six preserved terraces have been found in the paleo-dammed lake lacustrinesediments. These terraces are dual structures of sand to gravel layer and slit to claylayer with imbricated texture and they are initiated from the lake lacustrine sediments.These structures indicate that the terraces are piled by the dam bust, one bust formsone terrace. However, the dam bust of paleo-dammed Lake Maybe caused by seismicactivities.(5) The climate characteristics in each terrace have been found by investigatingthe environment proxies in the lake lacustrine sediments prior to each dam burst. Atthe same time, the basic cultural characteristics have been obtained by detailedinvestigation of Jinsha Ruins cultural layer. The comparison of these two climatecharacteristics shows the same sequence of climate changes. That is, with the decreaseof the height of the piles of terraces (i.e., the progress of Jinsha Ruins cultural layerthrough time), the climate change sequence (dry-wet-dry, cold-warm-cold) and thevegetation change process (lush-sparse-lush) are the same.(6) The environmental characteristics in the flooded phase of terrace areobtained from the test results of various environment proxies. This information iscompared to the environmental characteristics obtained from the analysis of the lakelacustrine sediments prior to each dam burst. It is concluded from the comparison thatwhen the geological environment changes toward the colder and wet climate,vegetation becomes lusher.(7) A variety of environmental proxies test results show that the ten(10)earthquake vestiges in the paleo-dammed lake lacustrine sediments is in a goodagreement with the ten (10) environmental change profiles. Therefore, the earthquakeInformation and the climate change information in the chosen region are related toeach other. |
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