Research on Shakemap of Peak Ground Acceleration With Bias Correction for Ludian Ms6.5 Earthquake on 3 Aug 2014

Abstract eng:
On 3 August 2014 a great earthquake of Ms6.5 struck Yunan province. The epicenter (27.1°N, 103.3°E) of the earthquake was located in Ludian county Zhaotong City, with a focal depth of 12km according to China Earthquake Administration. This catastrophic event caused extensive casualties and heavy engineering damage in a wide area. The earthquake caused 615 deaths, 114 missing and 3,000 people injured and a large number of houses collapsed and damaged. Considering the geological context, focal mechanism solutions, aftershock distribution, strong-motion peak accelerations and attenuation characteristics of the ground motion in western China, shakemap of PGA (Peak Ground Acceleration) for the Ludian was investigated. In order to reduce the uncertainty of the small value peak acceleration, this paper selected 22 strong-motion peak acceleration with PGA greater than 10gal, using Bias correction method to Correct ShakeMaps of the peak acceleration before. Considering the effect of local site effects, the PGAs of observation stations on surface were converted to the reference surface bedrock. Then abnormal data, outside three times the standard deviation of peak acceleration attenuation relationship, was excluded. Deviation factor (c0 = -2.89; c1 = 1.58) between observed value and estimated value of PGA attenuation relationship can be derived from the log-linear fitting peak acceleration. The estimates of PGA in area without stations were adjusted with the above deviation factor (c0, c1). Finally, considering the effects of local site, the estimates of PGA on bedrock were corrected to the value of the surface, interpolating with real observations to acquire the contour maps of peak ground acceleration. Relationship between PGA and intensity was consistent with the Chinese seismic intensity scale (GB17742-2008) The results shown that decay rate of the peak ground acceleration versus distance for this earthquake was faster than the peak acceleration attenuation relationship of Western China (derived from the 258 earthquake). Results of logarithmic bias correction were more consistent with attenuation of this earthquake. An area with PGA greater than 40gal after correcting is nearly 8,000 square kilometers, which is reduced by about 40%.

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