발파자료와 지진자료를 이용한 한반도의 상부지각 전단파 토모그라피

다국어 초록 (Multilingual Abstract)

This thesis presents the 3D variations of shear wave velocity of upper crust in the southern Korean Peninsula, estimated using the earthquake data as well as the KCRT KCRT - Korea Crust Research Team
refraction experiment data.
Short-period Rayleigh waves from the two crustal-scale seismic refraction profiles, KCRT2002 and KCRT2004, were analyzed to determine the shear wave velocity and attenuation structure of the uppermost crust in different tectonic regions of the Korean Peninsula and to examine if this can be related to the surface geology and tectonics of the study area. The refraction profiles were obtained using large explosive sources along a 294-km WNW？CESE line in 2002 and a 335-km NNW？CSSE line in 2004. The two refraction profiles, recorded on 2-Hz portable seismometers, contained Rayleigh waves in the period range of 0.2 to 1.2 s, and the distance range up to 30？C60 km from the sources. The profiles, which traverse four tectonic regions (Gyeonggi massif, Okcheon Fold belt, Yeongnam massif and Gyeongsang basin), were divided into twelve subsections based on the tectonic boundary and lithology. We obtained shear wave velocity models in the upper 1.5 km of the crust. The average shear wave velocity of the twelve subsections increases from ~2.4 km/s at the surface to ~3.2 km/s at 1.5 km depth. Overall, the shear wave velocities for the Okcheon fold belt and Gyeongsang basin are lower than those for the Gyeonggi and Yeongnam massifs by ~0.3 km/s. Shear wave velocity differences also exist among the subsections within the same tectonic region when there are distinct differences in lithology. We obtained the values of in the upper 0.6 km. for the Okcheon fold belt (~0.025) is approximately twice larger than for the massif areas (~0.012). The low shear wave velocity and high attenuation for the Okcheon fold belt seem to be related to the rock types of the area, which are mostly conglomerates and phyllites.
Upper crustal 3D shear wave velocity structure is estimated in the southern Korean Peninsula. Composing two different data sets in different period ranges, we obtained group velocities over an extended bandwidth. The inversion of the group velocities with the extended bandwidth secured better resolution and produced much better agreement between the group velocity data and the prediction from the inversion model. Our 3D images of the shear wave velocities correlate very well with the local geology and tectonics, showing low velocities in the Cretaceous sedimentary basins in the Gyeongsang basin and the Honam shear zone and high velocities in the Gyeonggi and Yeongnam massifs. The velocities of the Okcheon fold belt are lower than those of the two massifs and higher than those of the Gyeongsang basin. The velocity profiles of three tectonic zones, the two massifs and the fold belt, are different from the velocity profile of the Gyeongsang basin. While the three tectonic zones show a rapid increase from 2.6 km/s at the surface to 3.2 km/s at 1 km depth, followed by a gradual increase to 3.2 km/s at 3~4 km depth, and then a very slow increase to 3.5 km/s at 6~7 km depth, the Gyeongsang basin shows the steepest velocity gradient between 2~3 km depth. The depth of the Gyeongsang basin inferred from the steepest velocity gradient in the vertical velocity sections is estimated at ~3 km, while for the small basins along the Honam shear zone, it is estimated to be less than 2 km. High shear wave velocities are found in the NE area of the Gyeonggi massif and at the SW tip of the Yeongnam massif where the pre-Cambrian metamorphic complex is widespread.

목차 (Table of Contents)

• CHAPTER 1 INTRODUCTION 5
• 1.1. BACKGROUND AND IMPORTANCE 5
• 1.2. PREVIOUS STUDIES 6
• 1.3. RATIONALE AND PURPOSES 11
• 1.4. THESIS STRUCTURE 12
• CHAPTER 2 GEOLOGY AND TECTONICS OF THE STUDY AREA 13
• 2.1. GEOLOGY AND TECTONICS OF THE KOREAN PENINSULA 14
• 2.2. GEOLOGY IN THE VICINITY OF SHOT POINTS OF KCRT REFRACTION EXPERIMENTS 18
• CHAPTER 3 SHALLOW-DEPTH SHEAR WAVE VELOCITY STRUCTURES OF THE SOUTHERN KOREAN PENINSULA OBTAINED FROM TWO CRUSTAL REFRACTION PROFILES 22
• 3.1. DATA 23
• 3.2. ANALYSIS OF DATA 26
• 3.2.1. Group and Phase Velocities 26
• 3.2.2. Anelastic Attenuation Determination 35
• 3.2.3. Inversion for Shear Wave Velocity and Attenuation 36
• 3.3. RESULTS AND DISCUSSION 38
• 3.4. CONCLUSIONS 47
• CHAPTER 4 TOMOGRAPHY OF THE UPPER CRUSTAL Vs OF THE KOREAN PENINSULA CONSTRAINED BY SEISMIC REFRACTION AND EARTHQUAKE DATA 49
• 4.1. DATA 50
• 4.2. ANALYSIS OF DATA 54
• 4.2.1. Rayleigh Wave Group Velocities from Earthquake Data 54
• 4.2.2. Rayleigh Wave Group Velocities from Crustal Scale Refraction Data 54
• 4.3. RESULTS AND DISCUSSION 58
• 4.3.1. Lateral Variation of Rayleigh Wave Velocities from Earthquake Data 58
• 4.3.2. Limitation of The Narrow Band Surface Wave Inversion 71
• 4.3.3. Shear Wave Velocity Inversion Constrained by The Crustal-Scale Refraction Experiments 76
• 4.3.4. Tomographic Images of The Shear Wave Velocity 82
• 4.4. CONCLUSIONS 91
• CHAPTER 5 CONCLUSIONS AND DISCUSSION 93