Depth‐Dependent Crustal Scattering Attenuation Revealed Using Single or Few Events in South Korea

Abstract

Few studies have been conducted on the variance of scattering (![Graphic][1] ) and intrinsic attenuation (![Graphic][2] ) with depth in the crust. Furthermore, these values, routinely estimated using multiple lapse time window analysis (MLTWA), were seriously affected by different earthquake depths. Based on earthquakes recorded by dense seismic networks in South Korea, we used the MLTWA method on single or small clusters of events with similar depths. The depths of 54 earthquakes, relocated using seven velocity models, provide a typical seismogenic layer with the brittle–plastic transition (BPT) depth at 11 km, which correlated well with the seismicity of Korea. The depth was also used for the theoretical model based on the direct‐simulation Monte Carlo method. As the result of MLTWA, events with shallow focal depths exhibit higher ![Graphic][3] correlated with dense scatter, whereas those with deeper focal depths exhibit lower ![Graphic][4] . This depth dependency of the ![Graphic][5] value is indicated by the significant difference between the upper and lower parts of the BPT depth in the seismogenic layer. We also found that ![Graphic][6] values do not show depth dependency, whereas ![Graphic][7] values do. Thus, this study demonstrates for the first time that the crustal depth dependency of total (![Graphic][8] ) attenuation originates from ![Graphic][9] rather than from ![Graphic][10] . The approach using single or few events may be helpful for a regional study of ![Graphic][11] and ![Graphic][12] in seismically inactive regions for which insufficient data exist and may provide insight into the seismogenic layer related to potential seismic hazards. Online Material: Tables of residuals and range of multiple lapse time window analysis (MLTWA) parameters and Q −1 values for studied events. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif [6]: /embed/inline-graphic-6.gif [7]: /embed/inline-graphic-7.gif [8]: /embed/inline-graphic-8.gif [9]: /embed/inline-graphic-9.gif [10]: /embed/inline-graphic-10.gif [11]: /embed/inline-graphic-11.gif [12]: /embed/inline-graphic-12.gif