Source Parameters Estimation Methods Of Historical Earthquakes And Their Apllications

Macroseismic data of historical earthquakes refers to earthquake damage record in historical materials, which is the most basic and important data source in historical earthquakes study. Compared with only available instrumental parameters of earthquakes from modern seismic networks in several decades, it is extremely important to determine quantitatively source parameters of earthquakes occurred in long history to seismicity investigation and seismic hazard assessment. That is particularly true for counties such as China with more than2000years historical documents of damaged earthquakes.In this study, we briefly review the investigated methods in historical earthquakes study with their advantages and shortcomings, then we herein described a scheme to estimate historical earthquake source parameters based on basic principles and algorithms of Bayesian decision theory, model selection and multimodel inference.First we developed a method to preliminary estimate the strike of seismogenic fault using intensity data points and Bayesian decision theory. This method calculates the intensity discriminant expressions with the distribution of seismic intensity data based on Bayesian maximum posterior probability. The possible strike of seismogenic fault is analyzed according to the geometric shape of quadratic discriminant curves. The result of this method is repeatable without any other input of source parameters like epicenter or magnitude. This method passed the numerical tests for given strike values with random deviations, and the test of eight earthquakes with well inversion results of strike. Test results showed the method is unbiased statistically.Then a model selection method to quantitative estimate source parameters of historical earthquakes using macroseismic data and synthetic seismograms was described. This method enumerates all possible models with different source parameters (such as epicenter locations, focal depths and rakes), and obtains theoretic intensity distribution of each model from synthetic waveform modeling, then evaluates source models fitting degree for intensity data inferred from historical earthquake records to determinate its parameters. We used multiple model solutions and model weights to give quantitative uncertainty of source parameters caused by relatively scarce of historical information. This method was tested with bootstrap numerical cases for given sources with random deviations, and the well determined source parameters of the2004Parkfield M6.0earthquake. The test results showed that this method is robust statistically.Finally the scheme was applied to the1882Shenxian earthquake occurred in Hebei province, China. Source parameters estimation results shown that there were similar fitting degrees with different assumed strikes of seismogenic fault in NW, WE or NEE direction. Considered model selection results and geological results, the Shenxian earthquake is caused possibly by Jiuchengbei fault or Hezhuang fault, or Shenxi fault.