P파 초동주시와 표면파 분산곡선 역산을 통한 흙댐의 이상대 탐지

김기영 ( K. Y. Kim ),전광민 ( K. M. Jeon ),홍명호 ( M. H. Hong ),박영규 ( Young Kyu Park ) 한국지구물리·물리탐사학회 2011 지구물리와 물리탐사 Vol.14 No.1

To locate anomalous features including seepage pathways through the Daeryong earth-fill dam, P and Rayleigh waves were recorded along a 250-m profile on the crest of the dam. Seismic energy was generated using a 5-kg sledgehammer and detected by 24 4.5-Hz vertical-axis geophones installed at 3-m intervals. P-wave and apparent S-wave velocities of the reservoir dam and underlying bedrock were then inverted from first-arrival traveltimes and dispersion curves of Rayleigh waves, respectively. Apparent dynamic Poisson`s ratios as high as 0.46 were obtained at the base of the dam near its north-east end, where an outlet conduit occurs, and in the clay core body near the south-west end of the profile where the dam was repeatedly grouted to abate seepage before our survey. These anomalies of higher Poisson`s ratios in the upper part of clay core were also associated with effusion of grout on the downstream slope of the dam during post-survey grouting to abate leakage. Combining P-wave traveltime tomography and inversion of Rayleigh wave velocities was very effective in detecting potential pathways for seepage and previous grouted zones in this earthen dam.

청천댐 주변의 천부 P파 및 S파 속도구조

박영환 ( Yeong Hwan Park ),김기영 ( Ki Young Kim ) 한국지구물리·물리탐사학회 2013 지구물리와 물리탐사 Vol.16 No.3

On and near the 23-m high earthen Cheongcheon dam in Boryeong City, Korea, short seismic refraction and surface-wave profiles were conducted using a 5-kg sledgehammer. From vertical and horizontal components of the seismic waves, near-surface P-wave velocities (vp) and S-wave velocities (vs) were derived by inverting first-arrival refraction times and dispersion curves of Rayleigh waves. Average vp and vs for the Jurassic sedimentary basement were determined to be 1650 and 950 m/s at a depth of 30 m directly beneath the dam and 1650 m/s and 940 m/s at a depth of 10 m at the toe of the dam, respectively. The dynamic Poisson`s ratio for these strata were therefore in the range of 0.24 to0.25, which is consistent with ratios for consolidated sedimentary strata. Near a 45-m borehole 152 m downstream from the dam crest, an SH tomogram indicates a refraction boundary with an average vs of 870 m/s at depths of 10~12 m.At this site, the overburden comprises the upper layer with relatively constant vp and vs around 500 and 200 m/s, respectively, and the lower layer in which both vp and vs increase with depth almost linearly. The dynamic Poisson`s ratios for the overburden were in the range of 0.30 to 0.43.

표면파 토모그래피를 이용한 사우디아라비아의 S파 속도구조 및 이방성 연구

김린희,장성준,Martin Mai,Hani Zahran 한국지구물리.물리탐사학회 2019 지구물리와 물리탐사 Vol.22 No.1

이 연구에서는 사우디 아라비아 지역의 S파 속도구조와 이방성을 알아보기 위해 표면파 분산 곡선을 사용하여3차원 토모그래피를 수행하였다. 아라비아 반도는 지질학적 및 지형적으로 순상지(shield)와 플랫폼(platform)의 지형으로나뉜다. 본 연구에서는 사우디 지질조사소(Saudi Geological Survey)에서 받은 2008 ~ 2014년 기간의 규모 5.5 이상, 진앙거리 40° 이내인 지진 자료들을 사용하였다. 획득한 자료들은 전처리를 거쳐 다중 필터 기법(multiple filter technique) 을 적용하여 분산 곡선을 구하였다. 주기 5 ~ 140초에 해당하는 러브파와 레일리파의 군속도 분산 곡선을 역산하여 10 ~ 60 km에서의 SH파와 SV파 속도모델 그리고 이방성을 계산하였다. 그 결과 SV파의 속도모델에서는 순상지 하부 10 ~ 30 km 깊이에서 고속도 이상대를 보이며, 플랫폼 하부에서는 10 km 깊이에서 저속도 이상대를 보인다. 이는 순상지가 원생누대 기원의 오래되고 차가운 육괴로 되어있으며, 플랫폼이 고생대, 중생대, 신생대의 퇴적물로 덮여 있기 때문에이와 같은 결과가 나왔다고 판단된다. SV파와 SH파의 속도 차이를 이용하여 구한 이방성의 결과는 전반적으로 양의 이방성이 나타나며, 이는 자그로스 조산대에서의 섭입으로 인한 아라비아 판의 당김에 의해 인장력이 수평 방향으로 발생하여 SH파의 속도가 빠르게 나타난다고 판단된다. We perform a 3D tomographic inversion using surface wave dispersion curves to obtain S-velocity model and radial anisotropy beneath Saudi Arabia. The Arabian Peninsula is geologically and topographically divided into a shield and a platform. We used event data with magnitudes larger than 5.5 and epicentral distances shorter than 40° during 2008 ~ 2014 from the Saudi Geological Survey. We obtained dispersion curves by using the multiple filtering technique after preprocessing the event data. We constructed SH- and SV-velocity models and consequently radial anisotropy model at 10 ~ 60 km depths by inverting Love and Rayleigh group velocity dispersion curves with period ranges of 5 ~ 140 s, respectively. We observe high-velocity anomalies beneath the Arabian shield at 10 ~ 30 km depths and low-velocity anomalies beneath the Arabian platform at 10 km depth in the SV-velocity model. This discrepancy may be caused by the difference between the Arabian shield and the Arabian platform, that is, the Arabian shield was formed in Proterozoic thereby old and cold, while the Arabian platform is covered by predominant Paleozoic, Mesozoic, and Cenozoic sedimentary layers. Also we obtained radial anisotropy by estimating the differences between SH- and SV-velocity models. Positive anisotropy is observed, which may be generated by lateral tension due to the slab pull of subducting slabs along the Zagros belt.

Radial anisotropy along the Tethyan margin

Chang, Sung-Joon,van der Lee, Suzan,Matzel, Eric,Bedle, Heather Blackwell Publishing Ltd 2010 Geophysical journal international Vol.182 No.2

<P>SUMMARY</P><P>We estimate radial anisotropy along the Tethyan margin by jointly fitting regional <I>S</I> and Love waveform trains and fundamental-mode Love-wave group velocities. About 3600 wave trains with <I>S</I> and Love waves and 5700 Love-wave group velocity dispersion curves are jointly inverted for <I>SH</I>-velocity perturbations from a pre-existing, 3-D <I>SV</I>-velocity model. These perturbations are predominantly positive (<I>SH</I> faster than <I>SV</I>) and consistent with PREM, but our model also shows significant lateral variation in radial anisotropy that appears to be correlated with tectonic environment. <I>SH</I> waves travel faster than <I>SV</I> wave beneath backarc basins, oceans and orogenic belts such as the Tyrrhenian and Pannonian basins, the Ionian Sea, the Alps, the Apennines, the Dinarides and the Caucasus. The Algero-Provençal basin, however, is underlain by faster <I>SV</I> velocity. Faster <I>SV</I> velocity of radial anisotropy is also detected within cratons such as the East European platform and the Arabian shield. Beneath hotspots we detect a change in radial anisotropic polarity with depth, which may be caused by transition between the lattice-preferred orientation from horizontal deformation in the asthenosphere and the shape-preferred orientation from vertically oriented melt channels in the lithosphere. We also find significant portion of radial anisotropy within subducting slabs depends on the slab's dip angle.</P>

Three-dimensional surface wave tomography for the upper crustal velocity structure of southern Korea using seismic noise correlations

Jaehee Choi,강태섭,Chang-Eob Baag 한국지질과학협의회 2009 Geosciences Journal Vol.13 No.4

The cross-correlation technique was applied to ambient seismic noises to investigate the upper crustal velocity structure of the southern Korean Peninsula based on surface wave group velocities. We used seismograms recorded continuously during August 2005 at 91 accelerograph stations in the southern Korean Peninsula. From the correlation results of 4095 data pairs, the arrival times of Green’s functions along paths between stations of pairs were measured in discrete bins of frequency bands with central frequencies of 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, and 0.45 Hz. The spatial distribution of arrival times for each frequency band bin was inverted to obtain a two-dimensional tomographic map of Rayleigh wave group velocity. For each tomographic cell of the maps, we derived dispersion curves by extracting group velocities at center frequencies of the 7 frequency band bins. Shear-wave velocity obtained by depth inversion of the dispersion curve at each cell produced a one-dimensional velocity profile at depths. After aligning the profiles corresponding to tomographic cells, we obtained a three-dimensional uppermost crustal velocity model at depths down to approximately 8 km in the southern Korean Peninsula. These results show low-velocity distributions in the Gyeongsang Basin, western Gyeonggi Massif, and the area of Jeju Island and its northeastern coast. The Okcheon Fold Belt and Yeongnam Massif have relatively high velocity distributions. The low-velocity distribution in the Gyeongsang Basin shrinks in north-south direction at depths around 4 km and widens again with a tendency to migrate to the east as the depth is increased. However, the linear trend of low velocities in NNE-SSW direction at deeper depths (6.25–8.25 km) in the western area distinctively coincides with the western boundary of the Gyeongsang Basin. The background noise analysis in this study provided the constraining information for determination of depth variation in the shear-wave velocity distribution.

논문 : SH파 초동주시 역산과 표면파 분산곡선 역산으로부터 구한 횡파속도 단면 비교

이창민 ( Chang Min Lee ),김기영 ( Ki Young Kim ) 대한지구물리학회 2005 지구물리 Vol.8 No.2

Upper mantle shear wave velocity structure beneath northern Victoria Land, Antarctica: Volcanism and uplift in the northern Transantarctic Mountains

Graw, J.H.,Adams, A.N.,Hansen, S.E.,Wiens, D.A.,Hackworth, L.,Park, Y. North-Holland Pub. Co ; Elsevier Science Ltd 2016 Earth and planetary science letters Vol.449 No.-

The Transantarctic Mountains (TAMs) are the largest non-compressional mountain range on Earth, and while a variety of uplift mechanisms have been proposed, the origin of the TAMs is still a matter of great debate. Most previous seismic investigations of the TAMs have focused on a central portion of the mountain range, near Ross Island, providing little along-strike constraint on the upper mantle structure, which is needed to better assess competing uplift models. Using data recorded by the recently deployed Transantarctic Mountains Northern Network, as well as data from the Transantarctic Mountains Seismic Experiment and from five stations operated by the Korea Polar Research Institute, we investigate the upper mantle structure beneath a previously unexplored portion of the mountain range. Rayleigh wave phase velocities are calculated using a two-plane wave approximation and are inverted for shear wave velocity structure. Our model shows a low velocity zone (LVZ; ~4.24 km@?s<SUP>-1</SUP>) at ~160 km depth offshore and adjacent to Mt. Melbourne. This LVZ extends inland and vertically upwards, with more lateral coverage above ~100 km depth beneath the northern TAMs and Victoria Land. A prominent LVZ (~4.16-4.24 km@?s<SUP>-1</SUP>) also exists at ~150 km depth beneath Ross Island, which agrees with previous results in the TAMs near the McMurdo Dry Valleys, and relatively slow velocities (~4.24-4.32 km@?s<SUP>-1</SUP>) along the Terror Rift connect the low velocity anomalies. We propose that the LVZs reflect rift-related decompression melting and provide thermally buoyant support for the TAMs uplift, consistent with proposed flexural models. We also suggest that heating, and hence uplift, along the mountain front is not uniform and that the shallower LVZ beneath northern Victoria Land provides greater thermal support, leading to higher bedrock topography in the northern TAMs. Young (0-15 Ma) volcanic rocks associated with the Hallett and the Erebus Volcanic Provinces are situated directly above the imaged LVZs, suggesting that these anomalies are also the source of Cenozoic volcanic rocks throughout the study area.