| China has a long history of civilization and suffers of active seismicity,the recording of earthquake disaster is very early and the historical earthquake archivs are extremely abundant.Due to the short time period of seismic instrument recorded data,it is far from enough to study the seismic activity using such data.Historical earthquake research greatly expands the time span of seismic data and become the important base for seismological research and earthquake disaster mitigation.Owing to historical archives have complicated sources,moreover different politics,society,economics and historiography,the existing historical recording of earthquake damage is not complete.There might be a lot of hsitorical earthquakes omitted,especially in the remote region and earlier eras.The uncertainty of historical earthquake parameters is ubiquitous,and the ratio of the accuracy of epicenter location within 10km in the historical earthquake catalogue is only 2%,which will bring great difficulties and more uncertainty to practical applications.The traditional method to determine the historical earthquake parameters based on damage description is partly regulated by the level of detail of historical archives,so there might be without results in some cases.In this paper we combine several independent methods to amend the parameters of historical earthquakes together,and this will greatly improve the accuracy and reliability of historical earthquake parameters.We choose our research area at the capital city of Yunnan province,Kunming and subordinate counties and districts,the ranges of longitude and latitude are 102°E-104°E and 24.5°N-26.5°N respectively.There are 7 historical strong earthquakes,include Songming 8.0 earthquake in 1833.In our study,we select an optimal scheme to estimate historical earthquake parameters depend on individual situations of each historical earthquake.We reevaluate the intensity value of each intensity data point by carefully rechecking the damage records of historical archives and field trip.And then we apply intensity simulation or intensity numerical calculation based on the number of intensity data points and the distribution.For the historical earthquakes with fewer records,such as 1500 Yiliang 63/4 earthquake,1750 Chengjiang 61/4 earthquake and 1755 Yimen 61/2 earthquake,we apply the intensity simulation method.For the historical earthquakes with enough and well-documented records,we amend the earthquake parameters by using both the intensity simulation and the intensity numerical calculation.In order to make the abroad intensity numerical calculation more suitable for study area,drawing on the circle intensity distribution model of Bakun&Wentworh,we build the intensity attenuation equation for Yunnan province using survey assessed intensity data points from 25 instrumentally recorded earthquakes with magnitude between 5.0 and 6.6.We can estimate the epicentral location and intensity magnitude after calculating the intensity data points with the attenuation equation,and the result is good by comparing with the instrument seismic event.This method is applied to the parameters amendment of 1713 Xundian 61/2 earthquake,1725 Yiliang-Songming 63/4 earthquake.1733 Dongchuan 73/4 earthquake and 1833 Songming 8.0 earthquake.Finally we use the seismic density method to analyze the small and moderate earthquakes with magnitude greater than or equal to 2 from 1966-2019 in the research area.With the relationship between the seismic density and historical strong earthquakes,we can demonstrate the amendments of 7 historical earthquake parameters consistant with the seismic density,which by combing with the result of intensity simulation and calculation from intensity data points.The result shows the parameters of 6 earthquakes have been amended,especially the epicentral location of 1833 Songming earthquakes change significantly.The amended historical earthquake parameters have smaller errors and become more reasonable. |
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