| Popis: |
Surface wave dispersion is one of the essential means to study the structure of Earth’s crust and upper mantle. However, complicated structures of the Earth’s surface cause multipathing effects that make accurate phase measurement difficult. In this study, teleseismic Rayleigh-wave tomography was performed to estimate the crustal velocity structure of the southern part of the Korean Peninsula using phase differences between station pairs in a dense array instead of absolute phase arrival times and amplitudes. In order to estimate the phase change across the seismic array, the phase delay time between the nearby stations is inverted using the Eikonal equation. The structural velocity that is more consistent with the actual substructure is derived from adding the amplitude term to the inversion process by the Helmholtz equation. The earthquake data of 219 teleseismic events recorded at 146 broadband stations in the Korean Peninsula and Tsushima Island from 2018 to 2020 were used to build up Rayleigh wave phase velocity maps between the periods of 10 to 100 seconds. The teleseismic events were chosen with a magnitude of 6.0 or larger, a hypocenter depth shallower than 50 km, and an epicentral distance between 5˚ and 115˚. The final phase velocity maps for each period were obtained by stacking the results of the tomographic inversions of each event. Bayesian 1-D joint inversion using the phase velocity data of this study, those from ambient noise tomography and global velocity models is performed to obtain 3-D shear wave velocity models of the study region. The derived shear wave velocity maps show the clear boundary of velocity anomalies at short periods (≤ 20 s), which is parallel with the major geological structures, such as the Gyeongsang Basin and the Okcheon fold belt. At longer periods, we observe a significant velocity contrast between the southwestern and the northeastern region of the Korean Peninsula. |
