The Application Of Lichenometry To Paleoseismological Study In Western Sichuan

There are more than Ganzi-Yushu,Xianshuihe fault zone here distribution in Western Sichuan region,and since the Holocene fault frequent sexual activity,which often occur earthquake and paleo-earthquake.The largest slip rate in north western XSH can reach 10-15 mm/a by exploratory trench ancient earthquake,GPS observation measured the horizontal since the Holocene.But for the traditional research methods,in determining the ancient seismic events since the late Holocene,with bigger denudation rate is difficult to save sediment area,is likely to cause loss of the event.And for the age of ancient seismic events,traditional C14 dating is high precision,but is a given age range,is not the exact age.Lichen dating as a new means of dating,Austrian scholars Beschel put forward it in the last century 50 s,and began to used in the study of paleo-earthquake research,which made some progress in the late 70s.This paper via satellite imagery interpretation based on the analysis of previous data,,carried on the detailed field geological investigation,to determine the Zheduo Shan in Xianshuihe fault zone and Queer Shan in Ganzi-Yushu fault zone can undertake relevant lichen work.we choose Rhizocarpon geographicum lichen species for research in this two regions,we find that earthquake above magnitude 7 have a complete record since 1700 AD.So we measure the Rhizocarpon geographicum size in two areas;Under different ?x build their probability density curve respectively and compared with the historical earthquakes since 1700 AD which around 7 magnitude earthquake could correspond to the peak value and have a good corresponding relation.We find Zheduo Shan and Queer Shan probability density curve satisfy when ?x = 0.4 mm.Through the above research,mainly by the following understanding:1)There are no corresponding peak in Zheduo Shan and Queer Shan probability density curve when the magnitude is less than 6.5,When the magnitude is 6.5,one earthquake away from Queer Shan 270 km in 1738 can corresponding wave,but another in Qinghai Zhiduo in 1915 away more than 370 km from Queer Shan did not find on the peak value in probability density curve,it shows that not all the earthquake of magnitude 6.5 can produce rockfall with growth lichen,only in the distance less than 270 km;But the Diexi earthquake away 430km from Queer Shan has a correspond peak in probability density curve in Queer Shan which history magnitude Record is 6.5,but some think it is 7.It is only 7 can have peak there,So I think it is 7.The 1965 Daofu earthquake also have correspond peak in Zheduo Shan and Queer Shan probability density curve,but the record is only 5.0,1 think it maybe more than 5.0 even 6.5.When magnitude greater than 6.5,we found there are both no peak on the probability density curve for the chayu earthquake in 1950 AD which away 470 km from Queer Shan and 530 km from Zheduo Shan,the wudu earthquake in gansu with a magnitude 8.0 which away 450 km from Zheduo Shan and 550 km from Queer Shan also has no correspond peak in both probability density curves.It is Shows that the earthquake more than 6.5 can reduce rockfall only the distance is less than 430km.2)It is concluded that the growth curve of the two measurement region with regression analysis,the Rhizocarpon geographicum's growth rate is(0.07561 +0.00088)mm/a in Zheduo Shan,and(0.07284 + 0.00191)mm/a in Queer Shan.Of corresponding to the peak value of the earthquake since 1700 with rate can be concluded that the age,we found that with the gap between the real historical earthquakes within plus or minus 10 a,which show that the reliability of its nearly 300 years of dating.3)Compared to the probability density curve and exploratory trench ancient earthquake age of nearly 2000 years,we think there are corresponding peaks in Zheduo Shan curve to exploratory trench paleo-earthquake.There are only Xianshuihe faule and Ganzi—Yushu fault have ancient seismic section Within 400 km of Queer Shan.there is a range of peak value between 1700-1535 AD and 1030-831 AD,but it was not found the corresponding exploratory trench ancient seismic events on the main active faults in the area.In contrast,the history earthquake in Xianshuihe fault and Ganzi-Yushu fault has the certain regularity,but in 1700-1535 AD,1535-831 AD,it did not recorded earthquake performance,therefore,We suspect that there are lack of earthquake in this two Period in xianshui fault and Ganzi-Yushu fault.4)The probability density curve in Zheduo Shan and Queer Shan both maintained good continuity,it suggests the years of multiple earthquake from 1500 in two regional;In addition,we can see see probability density curve peaks' intensity is low from 500 AD to 1000 AD,and even some not wave exists.And the closer to 2000 AD,peak intensity is higher,not null values,it shows that earthquake recurrence period have a big trend from 500 AD.5)Compare the differences in growth rate in Zheduo Shan and Queer Shan,and integrated predecessors' study of Rhizocarpon geographicum,We think the temperature and precipitation can affect the growth rate of Rhizocarpon geographicum.In western Sichuan area,growth ratefor Rhizocarpon geographicum is consistent within the error range,it is 0.07284-0.07561 mm/a.