보고서 정보
주관연구기관 |
서울대학교 Seoul National University |
연구책임자 |
박창업
|
보고서유형 | 1단계보고서 |
발행국가 | 대한민국 |
언어 |
한국어
|
발행년월 | 2009-02 |
과제시작연도 |
2007 |
주관부처 |
기상청 |
사업 관리 기관 |
기상청 Korea Meteorological Administration |
등록번호 |
TRKO200900073889 |
과제고유번호 |
1365000418 |
사업명 |
기상지진기술개발사업 |
DB 구축일자 |
2013-04-18
|
키워드 |
지각속도구조.지진파형.전파시간.연합역산.복합위상.Crustal velocity structure.Waveform.Travel time.Joint inversion.Multiple phase.
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초록
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남한의 지진관측망에서 기록된 지진자료를 역해석하고, 지각규모 탄성파실험 결과로 얻어지는 자료를 분석하여 지각구조를 파악하였다. 이들 상호 보완적인 두 가지 방법을 병행하여 효과적으로 지각 속도구조를 도출하였다. 지진파자료 역해석에서는 고정관측소에 기록된 광대역 지진파형과 그 지진파 도달시간에 대해 연합역산법을 개발하고, 남한의 1차원적 지각속도구조와 지역적 속도구조를 얻었다. 광대역 지진자료의 수신함수를 이용하여 H-kappa 기법으로 남한의 지각두께분포와 Vp/Vs 값의 분포를 도출하였다. 2004년도에 수행한 연천-고성 간에 실
남한의 지진관측망에서 기록된 지진자료를 역해석하고, 지각규모 탄성파실험 결과로 얻어지는 자료를 분석하여 지각구조를 파악하였다. 이들 상호 보완적인 두 가지 방법을 병행하여 효과적으로 지각 속도구조를 도출하였다. 지진파자료 역해석에서는 고정관측소에 기록된 광대역 지진파형과 그 지진파 도달시간에 대해 연합역산법을 개발하고, 남한의 1차원적 지각속도구조와 지역적 속도구조를 얻었다. 광대역 지진자료의 수신함수를 이용하여 H-kappa 기법으로 남한의 지각두께분포와 Vp/Vs 값의 분포를 도출하였다. 2004년도에 수행한 연천-고성 간에 실시한 지각규모 광각반사 굴절파 실험에서 획득된 자료 중 P, S, PmP, SmS, PiP 등의 복합적 위상을 분석해석을 하였다. 또한 응용연구로서 오대산지진의 진원구조를 분석하였다.
Abstract
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Improvements are presented in modeling of crustal structures using receiver functions from teleseismic P waveforms. In order to overcome the nonuniqueness of receiver functions, phase velocities of Rayleigh waves were utilized as additional information. The two datasets complement each other, becaus
Improvements are presented in modeling of crustal structures using receiver functions from teleseismic P waveforms. In order to overcome the nonuniqueness of receiver functions, phase velocities of Rayleigh waves were utilized as additional information. The two datasets complement each other, because receiver functions are sensitive to shear wave velocity contrasts in layered structures, while surface wave dispersions are sensitive to averages of shear wave velocities. In order to avoid trapping in local minima, we performed forward modeling process which adopted the genetic algorithm (GA), a global optimization technique, instead of the linearized matrix inversion. GA is useful in regions where there is little a priori information about the crustal structures because it does not need a proper initial model. GA helped us to choose a more reasonable crustal structure model among many crustal structure models well fitting to observed receiver functions by searching the global minimum. Using several estimated models with different randomizing seed values, we could calculate standard deviations of velocities, which presented the stabilities of estimated crustal structure models quantitatively. We used this technique to estimate the crustal structures in southern Korea. The depths of the Moho discontinuity were estimated to be 30 km at the stations near the western shore, while those at the stations in the land were 33-35 km. The stabilities of the resolved crustal structures were well assured, for the standard deviations of estimated velocities were small.
We estimated Moho depths and $V_P$/$V_S$ ratios of the crust under 21 broadband stations in southern Korea using a grid search in the crustal thickness - $V_P$/$V_S$ ratio (H - $\kappa$) domain. The Moho depth varies from 25.9 km to 32.5 km, and the $V_P$/$V_S$ ratio ranges from 1.71 to 1.82in inland. Moho depths in the southernmost area of the Korean Peninsula were estimated shallower compared with those of the previous results obtained assuming a Poisson solid in the joint analysis of receiver functions and surface wave dispersion. This southernmost area is roughly in accord with the Yeongnam massif, where relatively high $V_P$/$V_S$ ratios of 1.78-1.82 are estimated. On the contrary, comparatively low $V_P$/$V_S$ ratio measurements (1.71-1.76) are generally distributed in the Gyeonggi massif which is located in the central area of the Korean Peninsula. The major factor for the high $V_P$/$V_S$ ratios in the Yeongnam massif is thought to be the plagioclase-rich mafic composition of the lower crust rather than partial melting or crustal fluids, because high crustal S wave velocities are reported in the Yeongnam massif. The mafic composition might have been supplied by the magmatic underplating. From the clearly divided feature of $V_P$/$V_S$ ratios in southern Korea and the $V_P$/$V_S$ ratio similarities between southern Korea and China, it seems that the Yeongnam massif might be related to the Sino-Korea craton, while the Gyeonggi massif to the Yangtze craton.
Results of analyses for the source parameters and ground responses of the 20 January 2007 Odaesan earthquake, Korea, are presented. We use the ground velocity and acceleration data recorded at the regional seismic stations located in southern Korea. For the determination of hypocenter and origin time, we use the program HYPO71 which has been generally used for the hypocenter determination of local earthquake and perform a depth phase analysis using arrival time difference of $P_n$ and $sP_n$ waves. The focal mechanism is obtained using a grid search algorithm with the polarities of the observed $P_g$, $P_n$ and SH waves. The moment magnitude ($M_w$) and dynamic stress drop are estimated using an iterative integral method with broadband seismic data. The estimated source parameters of the Odaesan earthquake are as follows: origin time 11:56:53.48 in UTC, latitude $37.686^{\circ}N$, longitude $128.589^{\circ}E$, focal depth 12.1 km, $M_w$ 4.5, dynamic stress drop 77.4 bars, the fault plane $19.69^{\circ}$, $69.74^{\circ}$ and $-165.02^{\circ}$, the auxiliary plane $284.40^{\circ}$, $75.97^{\circ}$ and $-20.91^{\circ}$ in strike, dip and rake, respectively. Considering geological characteristics around the epicenter, the fault plane solution with the strike angle of $19.69^{\circ}$ is consistent with that of the existing Woljeongsa fault. The largest peak ground acceleration (PGA), 0.157 g, was recorded at the DGY station located 7.5 km east of the epicenter. The maximum instrumental intensity is estimated as VII in the Modified Mercalli Intensity (MMI) scale.
For the simulation of ground motions, various seismic parameters are to be estimated in the region where the motions are applicable. One of the most important parameters is the spectral decay parameter $\kappa$. The spectral decay parameter $\kappa$ in conventional sense is for a regional area rather than for a local site. For the site-specific simulation of ground motions, however, a site-dependent spectral decay parameter should be estimated at an observation site. It is difficult to deduce the characteristics of each observation site using the conventional procedure. In order to obtain the site-dependent spectral decay parameter $\kappa$, we should estimate site-independent $\kappa_q$ and site-specific $\kappa_s$ successively. A procedure is to use the coda normalization method for the computation of $\kappa_q$ value as the first step followed by the next step, the computation of $\kappa_s$ for each site using the given $\kappa_q$ evaluated at the first step. For the application of the method, we used a total of 754 accelerograms from small earthquakes occurring in southern Korea from January 1999 to April 2003. After inversion process for $\kappa_q$, we obtained the $\kappa_q$ value of 0.0001382 sec/km in southern Korea. The $\kappa_s$ values are distributed from -0.15 to 0.35 second at 29 observation sites. The values of $\kappa_s$ are relatively large at the eastern and southern part of southern Korea. In addition, we also estimated the value of $\kappa_0$, distance independent term of $\kappa$ at regional area, as 0.007 second using all acceleration spectra in southern Korea.
목차 Contents
- 제 1 장 연구개발 과제의 개요 ...11
- 제 2 장 국내외 기술개발 현황 ...12
- 제 3 장 연구개발수행 내용 및 결과 ...13
- 제 4 장 목표달성도 및 관련분야에의 기여도 ...53
- 제 5 장 연구개발결과의 활용계획 ...55
- 제 6 장 연구개발과정에서 수집한 해외과학기술정보 ...56
- 제 7 장 참고문헌 ...57
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