Seismic Velocity Distribution Research Articles

Evidence of magma activation beneath the Harrat Lunayyir basaltic field (Saudi Arabia) from attenuation tomography

Abstract. We present a seismic attenuation model for the crust beneath the Cenozoic basaltic field of Harrat Lunayyir (western Saudi Arabia), where a strong seismic swarm occurred in 2009. The tomography inversion uses the envelope shape of the S wave seismograms from over 300 strong events (M < 3.5). The resulting attenuation structures appear to be consistent with the distribution of seismic velocities. The obtained 3-D attenuation model distinguishes the low-attenuation zones down to 5 km depth corresponding to the rigid basaltic cover. At greater depths, we detect a high-attenuation anomaly coinciding with the main seismicity cluster. We propose that this zone corresponds to the upper part of the conduit area ascending from deeper magma sources. According to the distributions of local events, fluids and melts from this conduit appear to reach a depth of ∼2 km, but were not able to reach the surface and cause the eruption in 2009.

Thermodynamic-Geophysical Modeling of the Interior Structure of the Siberian Cratonic Mantle along Cross-Cutting Profiles Kimberlite and Meteorite

Using a thermodynamic-geophysical approach, we map the 2-D interior structure of the Siberian cratonic mantle along the ultra-long cross-cutting seismic profiles Kimberlite and Meteorite carried out in Russia with peaceful nuclear explosions. There is a systematic decrease in temperature from west to east for the Kimberlite profile and a weak decrease from NW to SE for the Meteorite profile. Cratonic mantle shows a significant heterogeneity in the distribution of seismic velocities, temperature and density, topography of seismic boundaries and degree of layering at depths up to ~200 km reflecting somewhat different thermal state along both seismic profiles. Temperatures in the central part of the craton are somewhat lower than those at the periphery and 300-400°C lower than the average temperature in the surrounding mantle. A change of composition from depleted to fertile material reveals a negligible effect on seismic velocities that is practically unresolved by seismic methods, but remains the most important factor for the density increase of cratonic root. The distribution of density in the mantle cannot be attributed to any single composition, either depleted or enriched in basaltic components. This finding suggests a significant fertilization with depth and is compatible with the chemical stratification in the root of the craton. The thickness of the thermal boundary layer (TBL, conductive lid + transition layer) can be estimated as 300 ± 30 km thick along the Kimberlite and Meteorite profiles. At the base of the TBL, the temperature is close to 1450 ± 100°C isotherm; the calculated density corresponds to the PREM model density

MODELING WORKFLOW FOR DISTRIBUTION OF SEISMIC WAVES VELOCITIES IN THE CENTRAL PART OF DNIEPER-DONETS BASIN

In order to provide more detailed understanding for distribution of seismic velocities in central, most prospective for petroleum exploration, part of Dnieper-Donets Basin (DDB) a velocity model incorporating well VSP and onshore seismic data was built.

Computer model of seismic waves vertical velocity distribution for central part of the Dniprovsko-Donetsk depression

The article states the principles of layered media velocity modeling and the results of computer modeling of the value distribution of the vertical velocity of seismic waves in the central part of the Dnieper-Donets Basin. The computer model is used to integrate the seismic survey data, and to enhance the efficiency of seismic exploration for oil and gas. It is achieved through the application of new technologies for data processing with respect to velocity anisotropy, as well as through the use of traditional approaches. 

Peculiarities of distribution of seismic velocities in the Earth’s crust of the Kirovograd ore district of the Ingul megablock of the Ukrainian Shield. 2

As a result of studying the peculiarities of the seismic waves velocities in the Kirovograd ore district Earth’s crust and its structures some regularities of the velocity characteristics of the structures under studying were revealed. It is shown that these structures were confidently marked out in the field of the seismic wave velocities. It opens some new possibilities for tectonic zoning of the Kirovograd ore district and the Ukrainian shield territory.

Features of the distribution of seismic velocities in the earth's crust of the Kirovograd ore region of the Ingul megablock of the Ukrainian Shield. 1.

In consequence of studying of the peculiarities of the seismic waves velocities in the Kirovograd ore district and its structures Earth‘s crust some regularities of the velocity characteristic of the structures under studying were revealed. In following in construction of the complex 3D geology-geophysical model of the Kirovograd ore district Earth‘s crust these results may be used.

Waveform Retrieval and Phase Identification for Seismic Data from the CASS Experiment

The little destruction to the deployment site and high repeatability of the Controlled Accurate Seismic Source (CASS) shows its potential for investigating seismic wave velocities in the Earth's crust. However, the difficulty in retrieving impulsive seismic waveforms from the CASS data and identifying the seismic phases substantially prevents its wide applications. For example, identification of the seismic phases and accurate measurement of travel times are essential for resolving the spatial distribution of seismic velocities in the crust. Until now, it still remains a challenging task to estimate the accurate travel times of different seismic phases from the CASS data which features extended wave trains, unlike processing of the waveforms from impulsive events such as earthquakes or explosive sources. In this study, we introduce a time-frequency analysis method to process the CASS data, and try to retrieve the seismic waveforms and identify the major seismic phases traveling through the crust. We adopt the Wigner-Ville Distribution (WVD) approach which has been used in signal detection and parameter estimation for linear frequency modulation (LFM) signals, and proves to feature the best time-frequency convergence capability. The Wigner-Hough transform (WHT) is applied to retrieve the impulsive waveforms from multi-component LFM signals, which comprise seismic phases with different arrival times. We processed the seismic data of the 40-ton CASS in the field experiment around the Xinfengjiang reservoir with the WVD and WHT methods. The results demonstrate that these methods are effective in waveform retrieval and phase identification, especially for high frequency seismic phases such as PmP and SmS with strong amplitudes in large epicenter distance of 80–120 km. Further studies are still needed to improve the accuracy on travel time estimation, so as to further promote applicability of the CASS for and imaging the seismic velocity structure.

Time-lapse joint inversion of crosswell DC resistivity and seismic data: A numerical investigation

Time-lapse joint inversion of geophysical data is required to image the evolution of oil reservoirs during production and enhanced oil recovery, [Formula: see text] sequestration, geothermal fields during production, and to monitor the evolution of contaminant plumes. Joint inversion schemes reduce space-related artifacts in filtering out noise that is spatially uncorrelated, and time-lapse inversion algorithms reduce time-related artifacts in filtering out noise that is uncorrelated over time. There are several approaches that are possible to perform the joint inverse problem. In this work, we investigate the structural crossgradient (SCG) joint inversion approach and the crosspetrophysical (CP) approach, which are appropriate for time-lapse problems. In the first case, the inversion scheme looks for models with structural similarities. In the second case, we use a direct relationship between the geophysical parameters. Time-lapse inversion is performed with an actively time-constrained (ATC) approach. In this approach, the subsurface is defined as a space-time model. All the snapshots are inverted together assuming a regularization of the sequence of snapshots over time. First, we showed the advantage of combining the SCG or CP inversion approaches and the ATC inversion by using a synthetic problem corresponding to crosshole seismic and DC-resistivity data and piecewise constant resistivity and seismic velocity distributions. We also showed that the combined SCG/ATC approach reduces the presence of artifacts with respect to individual inversion of the resistivity and seismic data sets, as well as with respect to the joint inversion of both data sets at each time step. We also performed a synthetic study using a secondary oil recovery problem. The combined CP/ATC approach was successful in retrieving the position of the oil/water encroachment front.

Downward continued multichannel seismic refraction analysis of Atlantis Massif oceanic core complex, 30°N, Mid-Atlantic Ridge

[1] Detailed seismic refraction results show striking lateral and vertical variability of velocity structure within the Atlantis Massif oceanic core complex (OCC), contrasting notably with its conjugate ridge flank. Multichannel seismic (MCS) data are downward continued using the Synthetic On Bottom Experiment (SOBE) method, providing unprecedented detail in tomographic models of the P-wave velocity structure to subseafloor depths of up to 1.5 km. Velocities can vary up to 3 km/s over several hundred meters and unusually high velocities (∼5 km/s) are found immediately beneath the seafloor in key regions. Correlation within situand dredged rock samples, video and records from submersible dives, and a 1.415 km drill core, allow us to infer dominant lithologies. A high velocity body(ies) found to shoal near to the seafloor in multiple locations is interpreted as gabbro and is displaced along isochrons within the OCC, indicating a propagating magmatic source as the origin for this pluton(s). The western two-thirds of the Southern Ridge is capped in serpentinite that may extend nearly to the base of our ray coverage. The distribution of inferred serpentinite indicates that the gabbroic pluton(s) was emplaced into a dominantly peridotitic host rock. Presumably the mantle host rock was later altered via seawater penetration along the detachment zone, which controlled development of the OCC. The asymmetric distribution of seismic velocities and morphology of Atlantis Massif are consistent with a detachment fault with a component of dip to the southeast. The lowest velocities observed atop the eastern Central Dome and conjugate crust are most likely volcanics. Here, an updated model of the magmatic and extensional faulting processes at Atlantis Massif is deduced from the seismic results, contributing more generally to understanding the processes controlling the formation of heterogeneous lithosphere at slow-rate spreading centers.

Effects of CO<sub>2</sub> Injection on the Seismic Velocity of Sandstone Saturated with Saline Water

Geological sequestration (GS) of carbon dioxide (CO2) is considered as one of the most promising technologies to reduce the amount of anthropogenic CO2 emission in the atmosphere. To ensure success of CO2 GS, monitoring is essential on ascertaining movement, volumes and locations of injected CO2 in the sequestration reservoir. One technique is to use time-lapsed seismic survey mapping to provide spatial distribution of seismic wave velocity as an indicator of CO2 migration and volumes in a storage reservoir with time. To examine the use of time-lapsed seismic survey mapping as a monitoring tool for CO2 sequestration, this paper presents mathematical and experimental studies of the effects of supercritical CO2 injection on the seismic velocity of sandstone initially saturated with saline water. The mathematical model is based on poroelasticity theory, particularly the application of the Biot-Gassmann substitution theory in the modeling of the acoustic velocity of porous rocks containing two-phase immiscible pore fluids. The experimental study uses a high pressure and high temperature triaxial cell to clarify the seismic response of a sample of Berea sandstone to supercritical CO2 injection under deep saline aquifer conditions. Measured ultrasonic wave velocity changes during CO2 injection in the sandstone sample show the effects of pore fluid distribution in the seismic velocity of porous rocks. CO2 injection was shown to decrease the P-wave velocity with increasing CO2 saturation whereas the S-wave velocity was almost constant. The results confirm that the Biot-Gassmann theory can be used to model the changes in the acoustic P-wave velocity of sandstone containing different mixtures of supercritical CO2 and saline water provided the distribution of the two fluids in the sandstone pore space is accounted for in the calculation of the pore fluid bulk modulus. The empirical relation of Brie et al. for the bulk modulus of mixtures of two-phase immiscible fluids, in combination with the Biot-Gassmann theory, was found to satisfactorily represent the pore-fluid dependent acoustic P-wave velocity of sandstone.

Tracking repeated subduction of the Hikurangi Plateau beneath New Zealand

The Hikurangi Plateau has been subducted beneath New Zealand twice — firstly at ca. 100 Ma during N–S convergence with Gondwana, and currently during E–W convergence between the Pacific and Australian plates. Here we use a nationwide 3-D seismic velocity model derived from seismic tomography studies, and seismicity relocated with this model, to determine the location of the subducted western and southern edges of the plateau. In the Hikurangi subduction zone in the North Island and northern South Island we identify the western edge in the 37–140 km depth range, based on the distribution of seismic velocities in the top of the subducted Pacific plate, changes in the thickness of the dipping seismic zone, and steepening of the subducted plate downdip of the buoyant plateau. In the central South Island, where the Hikurangi Plateau is subducting for a second time, the plateau dips less steeply. Its southern edge is well-defined by the collision of the delaminated lower crust of the plateau with the northern Fiordland subduction zone, where it bends the younger subducted Australian plate to vertical. The Hikurangi Plateau was originally rifted from the Ontong Java Plateau, and the subducted portions of the Hikurangi Plateau identified here fill a gap in reconstructions of this large igneous province.

Seismic imaging of the 2001 Bhuj Mw7.7 earthquake source zone: b-value, fractal dimension and seismic velocity tomography studies

We use precisely located aftershocks of the 2001 Mw7.7 Bhuj earthquake (2001–2009) to explore the structure of the Kachchh seismic zone by mapping the 3-D distributions of b-value, fractal dimension (D) and seismic velocities. From frequency–magnitude analysis, we find that the catalog is complete above Mw = 3.0. Thus, we analyze 2159 aftershocks with Mw ≥ 3.0 to estimate the 3-D distribution of b-value and fractal dimensions using maximum-likelihood and spatial correlation dimension approaches, respectively. Our results show an area of high b-, D- and Vp/Vs ratio values at 15–35 km depth in the main rupture zone (MRZ), while relatively low b- and D values characterize the surrounding rigid regions and Gedi fault (GF) zone. We propose that higher material heterogeneities in the vicinity of the MRZ and/or circulation of deep aqueous fluid/volatile CO 2 is the main cause of the increased b-, D- and Vp/Vs ratio values at 15–35 km depth. Seismic velocity images also show some low velocity zones continuing in to the deep lower crust, supporting the existence of circulation of deep aqueous fluid / volatile CO 2 in the region (probably released from the eclogitasation of olivine rich lower crustal rocks). The presence of number of high and low velocity patches further reveals the heterogeneous and fractured nature of the MRZ. Interestingly, we observe that Aki (1981)'s relation (D = 2b) is not valid for the spatial b-D correlation of the events in the GF (D 2 = 1.2b) zone. However, the events in the MRZ (D 2 = 1.7b) show a fair agreement with the D = 2b relationship while the earthquakes associated with the remaining parts of the aftershock zone (D 2 = 1.95b) show a strong correlation with the Aki (1981)'s relationship. Thus, we infer that the remaining parts of the aftershock zone are probably behaving like locked un-ruptured zones, where larger stresses accumulate. We also propose that deep fluid involvement may play a key role in generating seismic activity in the MRZ, therefore, a similar episode of deep fluid inflow could play a crucial role in causing the next strong earthquakes in the surrounding blocks of NWF.

Compressive deformations and stress propagation in intracontinental lithosphere: Finite element modeling along the Dinarides–East European Craton profile

Neotectonic stage stress and strain evolution was analyzed along a vertical lithospheric profile crossing the Dinarides, Pannonian Basin, Carpathians and East European Craton. A structural and lithological model was constructed based on distribution of seismic wave velocity along the Cel05 deep seismic sounding line. Rheological properties of each lithospheric layer were calculated as an average value for component rocks. In the applied model a highly laterally heterogeneous section of the lithosphere underwent 2.5% of shortening during 7.5Myr, which corresponds to neotectonic inversion of the Pannonian–Carpathian–Dinaric region. The coupled viscoelastoplastic model predicts stress regime changes, within mechanically partitioned lithosphere, that together with complex rheological properties controls the deformation pattern. Long-wavelength lithospheric buckling was initiated during the first stage of inversion. It was followed by development of short wavelength minor folding in the detached upper crust. The topographic surface within the basin and over the transition to adjacent tectonic units was modified by buckling and swelling mechanisms producing folds of 800m amplitude. Buckling, more efficient in the initial stage of inversion, was over time substituted by crustal swelling that contribute to raising anticlines at the topographic surface due to isostatic compensation. Compound mechanism of folding causes migration of anticlines at the topographic surface and synclines at Moho, which finally produces gentle pinch-and-swell pattern in the crust. Efficient mechanism of continental lithosphere buckling was described under minor shortening and a low stress level.

Estimation of the correlation structure of crustal velocity heterogeneity from seismic reflection data

SUMMARY Numerous sources of evidence point to the fact that heterogeneity within the Earth’s deep crystalline crust is complex and hence may be best described through stochastic rather than deterministic approaches. As seismic reflection imaging arguably offers the best means of sampling deep crustal rocks in situ, much interest has been expressed in using such data to characterize the stochastic nature of crustal heterogeneity. Previous work on this problem has shown that the spatial statistics of seismic reflection data are indeed related to those of the underlying heterogeneous seismic velocity distribution. As of yet, however, the nature of this relationship has remained elusive due to the fact that most of the work was either strictly empirical or based on incorrect methodological approaches. Here, we introduce a conceptual model, based on the assumption of weak scattering, that allows us to quantitatively link the second-order statistics of a 2-D seismic velocity distribution with those of the corresponding processed and depth-migrated seismic reflection image. We then perform a sensitivity study in order to investigate what information regarding the stochastic model parameters describing crustal velocity heterogeneity might potentially be recovered from the statistics of a seismic reflection image using this model. Finally, we present a Monte Carlo inversion strategy to estimate these parameters and we show examples of its application at two different source frequencies and using two different sets of prior information. Our results indicate that the inverse problem is inherently non-unique and that many different combinations of the vertical and lateral correlation lengths describing the velocity heterogeneity can yield seismic images with the same 2-D autocorrelation structure. The ratio of all of these possible combinations of vertical and lateral correlation lengths, however, remains roughly constant which indicates that, without additional prior information, the aspect ratio is the only parameter describing the stochastic seismic velocity structure that can be reliably recovered.

Geophysical model of the lithosphere across the Variscan Belt of SW-Iberia: Multidisciplinary assessment

A multidisciplinary geophysical study along a large seismic transect in the SW-Iberian Peninsula has been carried out. This study integrates the crustal structure, geometry and composition obtained from normal incidence and wide-angle seismic reflection data with other observables (geoid, gravity and topography). The internal architecture of the lithosphere across the Variscan Orogen of SW-Iberia is constrained by the 300 km long high resolution deep normal seismic reflection IBERSEIS Transect. The most prominent feature imaged by the seismic survey is the Iberseis Reflective Body (IRB), a 140 km long high amplitude reflective body located in the middle crust of the northern half of the transect. The seismic velocity (Vp) distribution within the crust and the upper mantle is constrained by two wide-angle seismic transects acquired in the same area. The velocity models show a complex crust, with a specially complex middle crust, which features higher velocities than the average continental crust. Also the wide-angle data revealed that the IRB is characterized by high velocities. This feature was then interpreted as sill-like structure built up by a series of mafic intrusions. Therefore, a key issue is to study if this relatively mafic crust is consistent with other geophysical observables. Based on the velocity models, two lithospheric density models have been derived along the IBERSEIS wide-angle transects. The geoid, gravity and topography response of these models have been calculated using a finite elements code that solves, simultaneously, the geopotential, lithostatic, and heat flow equations. The resulting values are then compared with the measured observables and the crustal and lithospheric mantle geometry and density is modified until the best fit is obtained. The initial density models calculated from the seismic data adjust quite well to the real potential field data. However, minor modifications have been required in order to properly fit the observables. The final density models are consistent with the existence of relatively high density bodies in the mid-crust providing further support to the seismic interpretation. In addition, they place new constraints on the location of the lithosphere–asthenosphere boundary and on the tectonic evolution of SW-Iberia.

Exploring the Groß Schönebeck (Germany) geothermal site using a statistical joint interpretation of magnetotelluric and seismic tomography models

Exploration for geothermal resources is often challenging because there are no geophysical techniques that provide direct images of the parameters of interest, such as porosity, permeability and fluid content. Magnetotelluric (MT) and seismic tomography methods yield information about subsurface distribution of resistivity and seismic velocity on similar scales and resolution. The lack of a fundamental law linking the two parameters, however, has limited joint interpretation to a qualitative analysis. By using a statistical approach in which the resistivity and velocity models are investigated in the joint parameter space, we are able to identify regions of high correlation and map these classes (or structures) back onto the spatial domain. This technique, applied to a seismic tomography-MT profile in the area of the Groß Schönebeck geothermal site, allows us to identify a number of classes in accordance with the local geology. In particular, a high-velocity, low-resistivity class is interpreted as related to areas with thinner layers of evaporites; regions where these sedimentary layers are highly fractured may be of higher permeability.

Distribution of Seismic Velocities and Attenuation in the Crust beneath the North Anatolian Fault (Turkey) from Local Earthquake Tomography

We investigate the crustal structure beneath the western part of the North Anatolian fault zone (NAFZ), an area where at least five damaging earthquakes occurred during the twentieth century. This study is based on local earthquake tomography using the data from aftershocks of the Izmit event (17 August 1999, M 7.4) recorded by stations of permanent and temporary networks. We derive the distribution of V P , V S , and the V P / V S ratio based on the iterative inversion for both V P - V S and V P - V P / V S using the LOTOS code. Innovatively, in this study we perform an inversion for frequency-dependent S -wave attenuation (1/ Q S ). The reliability of the results is assessed through synthetic tests. The distributions of the resulting seismic parameters ( V P , V S , V P / V S , and Q S ) highlight important geodynamical features in the study area. The low-velocity and high-attenuation patterns mostly correlate with the fracturing zones of the NAFZ. Low velocities are also observed beneath the main sedimentary basins (e.g., Adapazari, Duzce, and Kuzuluk). High-velocity and low-attenuation patterns correlate with blocks presumed to be rigid (Kocaeli, Armutlu, and Almacik blocks). The rupture traces of the largest earthquakes in this area pass generally in the transition areas between high and low velocities, while moderate and weak seismicity is mostly concentrated in low-velocity areas. Based on these results we propose and discuss the role that the Almacik block could have played in producing the largest earthquakes in the study area in the twentieth century.

Seismic Tomography Investigation in 140m Gallery in the Horonobe URL Project

AbstractThe Japan Atomic Energy Agency (JAEA) established the Horonobe Underground Research Laboratory (URL) Project at Horonobe, in Hokkaido, Japan to enhance reliability of nuclear waste disposal technologies to be developed in deep sedimentary environments. JAEA has undertaken a number of in-situ experiments to determine changes in the properties of the host rock and the extent of the excavation disturbed zone (EDZ) created by the excavation of underground galleries for the disposal of radioactive waste. This paper reports a seismic tomography survey (using a hammer seismic source) of the “140m Gallery” at a depth of 140m below the surface of the Horonobe URL. The observation area was 3m square on the horizontal plane along the sidewall of the 140m Gallery. The measurement was repeated with the progress of excavation of a tunnel. In this experiment, the distribution of seismic velocity in the rock around the new tunnel and its decrease as the tunnel was dug, were observed using a simple small-scale seismic tomography system. The data collected show that this system can be used to capture the EDZ around tunnels.

Efficient and Accurate Calculation of Ray Theory Seismic Travel Time through Variable Resolution 3D Earth Models

Realistic 3D models of the seismic velocity distribution within the Earth have the potential to significantly improve our ability to accurately and precisely locate seismic events around the world ( e.g. , Flanagan et al. 2007). Development of these models by tomographic inversion of observed seismic travel times and the use of such models in seismic event location calculations, require the ability to accurately and efficiently compute predicted source to receiver travel times through 3D velocity structures. Meeting these requirements on a global scale presents two fundamental challenges: 1) how to represent the 3D distribution of seismic velocity in the Earth in models that can be interpolated efficiently, and 2) how to efficiently and accurately compute predicted travel times through these models. We present a 3D variable-resolution modeling methodology and a travel time prediction algorithm based on ray theory that address these issues and are compatible with computational resources ranging from laptop computers to powerful distributed computing systems. A simple representation of the 3D distribution of Earth properties is a regular latitude-longitude grid over the surface of the Earth with grid nodes distributed in an irregular manner in the radial direction (Figure 1A). Finding the grid cell in which an arbitrary point is located in such a model is both straight-forward and efficient. For models that do not extend to polar regions ( e.g. , Pasyanos et al. 2004), this approach provides satisfactory performance, but for global models such as the Crust 2.0 model (Bassin et al. 2000; http://igppweb.ucsd.edu/~gabi/crust2.html) the approach suffers from the fact that meridians intersect at the poles, leading to much smaller grid cells at high latitudes than at the equator, when cell size is evaluated in km2. Over the past couple of decades gridless Earth model representations and several representations involving irregular meshes have been …

여수시 묘도 부근 퇴적암과 안산암에서 물리검층에 대한 자료해석

여수시 묘도 일대에 분포하는 안산암과 퇴적암 지역에서 물리검층 종류인 부유식 P S파 속도검층과 밀도검층을 실시하였다. 연구목적은 이 지역에 분포하는 두 암상에 대해 깊이에 따른 탄성파속도 및 밀도분포를 찾아내어 시추조사를 통해 얻은 지반정보인 암상과 RQD 값을 비교하여 암석 종류에 따른 상호간에 상관관계를 파악하는 것이다. 연구지역에서 두 암석에 대한 탄성파 속도 분포는 깊이에 따라 P파가 약 2,000m/sec 내외이며, S파가 1,500m/sec 내외의 차이를 보였으며, 밀도는 깊이에 따라 약 <TEX>$0.35g/cm^3$</TEX>의 차이로 비교적 넓은 폭으로 나타났다. 이러한 결과는 암석 종류에 대한 차이보다 풍화 정도에 따른 것으로 해석된다. 그러나 RQD, 탄성파속도 및 밀도의 상관성 분석은 비교적 높은 관계를 보이므로 물리 검층자료의 결과를 이용하여 RQD에 관련된 불연속면의 빈도를 유추할 수 있다고 본다. We carried out the Suspension PS log and gamma-gamma log in andesite and sedimentary rocks distributed near the area of Myodo-dong, Yeosu. The main purpose of this study was to find out the distribution of seismic velocities and densities and to analyze the correlation of the two rocks by comparing their geophysical well logs with rock cores. The distributions of P and S-wave velocities for two rocks represented in the study area showed a difference of about 2,000 m/sec and 1,500 m/sec with depth, respectively, while the distributions of densities had a discrepancy of about <TEX>$0.35g/cm^3$</TEX> with depth. However, the results of geophysical well logs analysis were similar to the two rocks. Consequently, it is clear that these results are interpreted as a difference due to weathering rather than rock type. In particular, the RQD values showed a good correlation to geophysical well log data.