Estimation of Source Characteristics of Large Plate Boundary Earthquake Based on Spectrum Inversion Analysis

-Investigation of near the Source Region of the 1985 Mexico Earthquake and the 2015 Chile Earthquake-

Abstract

The 19 September 1985 Michoacan, Mexico earthquake (M_W 8.0) and the 16 September 2015 Illapel, Chile earthquake (M_W 8.3) were mega thrust earthquakes occurred under continental areas, and a number of seismic records were observed above the source regions.

We estimated source spectra, Q value and site amplification factors by spectral inversion analysis. Based on the source spectra, we estimated the short-period amplitude level and the stress drop.

The stress drop slightly showed focal depth dependency although the variation was large. The estimated short-period level of the 1985 Mexico earthquake is half of the level obtained from the conventional study, whereas that of the 2015 Chile earthquake corresponds to the average level.