17:15 〜 19:15
[SIT19-P07] Constraints on crustal seismic properties of the southern Korean Peninsula using Virtual Deep Seismic Sounding and their tectonic implications
キーワード：Crustal structure, Body waves, Virtual Deep Seismic Sounding
The southern Korean Peninsula (SKP) preserves a complex history of geologic events in Northeast Asia, featuring the Permian–Triassic collision between the North China Craton (NCC) and the South China Craton (SCC), along with the formation of the Japanese island arc system during the Neogene. Traces of these events are evident through tectonic units trending NE–SW to NNE–SSW in the SKP. Knowledge of the average P-wave velocity (VP), thickness (H), and P-to-S velocity ratio (VP/VS) of the continental crust can provide key information on its composition, isostasy, and thermal interactions with the upper mantle. In this study, we constrain these properties of the SKP crust by performing a joint analysis of Virtual Deep Seismic Sounding (VDSS) and P-wave receiver function (PRF). For VDSS, we inverted for H and VP by fitting traveltimes and phases of direct S and SsPmp from teleseisms recorded by 193 stations (108 broadband seismometers and 155 accelerometers) in the SKP. The inherent large amplitude of SsPmp, along with the removal of source-side scattering effects via deconvolution of S-type waves separated by particle motion analysis, facilitates robust waveform fitting.
Estimates of VP and H range within 6.0–6.7 km/s and 23–34 km, respectively, whereas values of VP/VS, derived from the differential arrivals of direct and multiple P-to-S conversions in the PRF combined with VP and H from VDSS, mostly lie within 1.66–1.82. An independent assessment of H and VP/VS from H–VP/VS stacking (Zhu and Kanamori, 2000), fed by VP from VDSS, shows a similar trend overall, reinforcing the validity of our results. A comparison of crustal compositions inferred from the obtained VP and VP/VS with those from the rock samples indicates an abundance of typical metamorphic rocks and granites, with compositions transitioning from felsic to intermediate toward the southeast. VP exceeding 6.4 km/s in the southern region of Yeongnam Massif and Gyeongsang Basin might indicate magmatic underplating during the Cretaceous, caused by the subduction of the Izanagi Plate. Low VP in the uppermost mantle, inferred from the phase shift between direct S and SsPmp, in addition to high gravity anomaly in that region, implies a probable existence of magmatic underplate in the lower crust and associated granulitization in the surroundings. A similar value in the southwestern portion of the Okcheon Belt appears to stem from rifting between Precambrian massifs during the Paleozoic era. A shallow Moho (23–25 km) on the eastern coast shows evidence for the opening of the East Sea (Sea of Japan). VP in the Yeongnam Massif and Gyeongsang Basin exhibits similarities to NCC, while those are significantly lower in the Gyeonggi Massif at similar latitudes. This discrepancy, together with lower VP/VS in the Gyeonggi Massif, suggests the possibility of its different tectonic origin compared to other units.
Estimates of VP and H range within 6.0–6.7 km/s and 23–34 km, respectively, whereas values of VP/VS, derived from the differential arrivals of direct and multiple P-to-S conversions in the PRF combined with VP and H from VDSS, mostly lie within 1.66–1.82. An independent assessment of H and VP/VS from H–VP/VS stacking (Zhu and Kanamori, 2000), fed by VP from VDSS, shows a similar trend overall, reinforcing the validity of our results. A comparison of crustal compositions inferred from the obtained VP and VP/VS with those from the rock samples indicates an abundance of typical metamorphic rocks and granites, with compositions transitioning from felsic to intermediate toward the southeast. VP exceeding 6.4 km/s in the southern region of Yeongnam Massif and Gyeongsang Basin might indicate magmatic underplating during the Cretaceous, caused by the subduction of the Izanagi Plate. Low VP in the uppermost mantle, inferred from the phase shift between direct S and SsPmp, in addition to high gravity anomaly in that region, implies a probable existence of magmatic underplate in the lower crust and associated granulitization in the surroundings. A similar value in the southwestern portion of the Okcheon Belt appears to stem from rifting between Precambrian massifs during the Paleozoic era. A shallow Moho (23–25 km) on the eastern coast shows evidence for the opening of the East Sea (Sea of Japan). VP in the Yeongnam Massif and Gyeongsang Basin exhibits similarities to NCC, while those are significantly lower in the Gyeonggi Massif at similar latitudes. This discrepancy, together with lower VP/VS in the Gyeonggi Massif, suggests the possibility of its different tectonic origin compared to other units.