Multiple Lapse Time Window Analysis Study Using Single Earthquake in the South Korea

Abstract:

Single earthquake data was used to separate Q_i^-1 and Q_s^-1 for South Korea (S. Korea) with the Multiple Lapse Time Window Analysis (MLTWA). The MLTWA method have been used numerous earthquake data at once to simulate the energy of observed seismic envelopes with theoretical values obtained by a single source assumption. The theoretical values of MLTWA method is normally obtained by numerical method such as Direct Simulation Monte Carlo (DSMC) method due to availability for various source depth. One of the major concerns with the MLTWA method is that, it normally shows a large observational scatter caused by the multiple use of earthquakes which have different radiation pattern and focal depth, and the regional alteration of local structure. Recently our study of MLTWA using single event showed realistic results when the number of recorded station was more than 8, without consideration of radiation pattern in DSMC method (Asep et al., 2015). In particular, Asep et al. (2015) found the significant effect of source depth which had been neglected by the previous MLTWA studies (Asep et al. (2015). This study, therefore, focused on the depth effect of MLTWA by relocation of 53 earthquakes occurred in S. Korea from March 2003 to December 2014. To obtain reliable depths of these events, seven crustal models (Fig. 1) were constructed based on two refraction profiles across the Korean Peninsula. The Vp/Vs ratio and the preliminary origin time (POT) was obtained by the Wadati plot. Since focal depth and origin time is a coupled data, a series of inversions using HYPO71 were performed for only three parameters (latitude, longitude, and origin time) of earthquakes while keeping its depth fixed each time. The residuals were calculated for varied focal depth from 0 to 30 km with an increment of 0.5 km, and depth range of minimum rms residual (minimum rms residual plus 0.05) was selected. For the minimum depth range of seven models, the closest range with the POT was selected as the most reliable depth range. Based on this reliable depth, MLTWA using single event showed good correlation between scattering attenuation value and depth (presently processing).