3-D Velocity Structures of the Uppermost mantle beneath the Southern Korean Peninsula from Pn and Sn Tomography
Abstract
The crust and upper mantle beneath the Korean peninsula have evolved through a variety of tectonic processes including continental collisions, extensions, and arc-backarc tectonics, which are accompanied with widespread magmatic intrusions and volcanic eruptions. Therefore, investigations on the structures of the uppermost upper mantle with spatial variations in the Moho are essential to understand the detailed tectonic history. In this study, we obtained high-resolution tomographic images of P- and S-wave velocity using the Moho refracted waves (i.e., Pn and Sn). Because P and S- wave velocity have different sensitivity on the factors that influence the seismic velocities (e.g., composition, temperature, anisotropy, partial melting), joint interpretation of P and S velocity models can provide more constraints on properties of the upper mantle. Arrival times of 5,407 Pn and 4,017 Sn, were manually picked from seismic data of 348 stations for the 65 events consisting of 60 events around the southern Korean Peninsula and five events in Japan. The hypocenters of the 60 events that occurred across the Korean peninsula were relocated by using Non-linear inversion algorithm (Nonlinloc) with the 1-D regional crustal velocity model. The curvature of the Moho was considered with a 3-D Fast marching ray-tracing method to reflect the characteristics of the refracted waves that propagate the 3-D structures below the interface. Checkerboard resolution test shows that the tomographic models have high resolution on the whole southern Korean peninsula and its margin. The result for Pn tomography showed the pattern of dividing into fast velocity on the Gyeonggi Massif and slow velocity on the Youngnam Massif and Gyeongsang Basin, based on the Okcheon Belt. In case of the Gyeonggi Massif, the slow S-wave velocity (~4.35km/sec) and a high Vp/Vs ratio (~1.81) was detected. The Yeonil Basin where the Paleogene volcanic rocks are distributed was represented as a region having the lowest Vs (~4.3 km/sec) with a relatively high Vp/Vs ratio (~1.78). The result for Vp/Vs ratio presented a striking NE-SW low Vp/Vs ratio (~1.7). Considering that the S wave is sensitive to temperature and shows relatively low, the high Vp/Vs ratio on the Gyeonggi Massif suggests the possibility of a high geothermal gradient because of the thin lithosphere. The low Vp/Vs ratio consistent with the geological boundary is inferred as the Mesozoic plutonic rocks. Our models show the evidence of heterogeneous crustal growth and modification processes through complex tectonic history during the Mesozoic and Cenozoic at the East Asia continental margin.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.T45E..01K