Separation of Intrinsic and Scattering Attenuation Using Single Event Data in South Korea

Monday, 15 December 2014
Asep Nur Rachman1, Tae-Woong Chung1 and Kazuo Yoshimoto2, (1)Sejong University, Seoul, South Korea, (2)Yokohama City University, Yokohama, 236, Japan
Qiand Qsvalues are mainly obtained by the Multiple Lapse Time Window Analysis (MLTWA) with comparison of observed seismic wave envelopes with theoretical values. MLTWA observations require numerous data from multiple earthquakes inevitably causing large scatter by the facts - radiation pattern, focal depth, and regional alteration - which are neglected by theoretical simulation currently assuming a single source.

MLTWA using single earthquake data may, therefore, be helpful to reduce observational scatter by considering radiation pattern, focal depth, and regional alteration. To take into account radiation pattern of single event data, focal mechanism algorithm is implanted to code of DSMC method. In addition, this study selected data from the previous study using focal depth of about 10 km and compared the results between single events and multiple events.

MLTWA using single event provided stable results for all frequencies if number of recorded station is 10 or/and more. Although only focal depth and regional alteration was considered excluding radiation pattern, result of MLTWA using single event showed plausible results by regional combination - Q-1 values of two regionally reliable events are selected as the lower and upper bounds. By this combination, the three zones of Q-1 values were obtained for A as Gyeongsan Basin, B as western plain region, and C as rugged terrain such as mountainous region and sea with abrupt change of depth. The Q-1 values in descending order are C, A, and B, remarkable of which is at low frequencies of Qs1. The values of Zone A and B correlate well with those of regional QLg1 at 1 Hz. The highest Q1 of zone C correlates with the result of worldwide studies showing high Qvalues by the effect of lateral path propagating through high mountainous region.

In Fig. 1, Qvalues generally correlate with tectonic activity and volcanism, measured hypocentral distance, and focal depth of event data. In addition, high Qvalues are observed for the regions including zone C by the effect of lateral path propagating through high mountainous region. This path effect seems to be required a quantitative analysis by using tomographic approaches.

Fig. 1. Comparison of Qs−1 from this study (Zone A, B, and C) with those from the other studies including worldwide regions.