Seismic Velocity Values Research Articles

Engineering applications of seismic refraction method: A field example at Wadi Wardan, Northeast Gulf of Suez, Sinai, Egypt

Fourteen shallow seismic refraction profiles were conducted in Wadi Wardan, northeast Gulf of Suez, Sinai to delineate some of the shallow soil engineering characteristics for construction purposes. Both compressional (P) and shear (S) waves were acquired and interpreted using Generalized Reciprocal Method (GRM) then the resulted velocity-depth model is verified using a Finite Difference (FD) method to improve the final velocity-depth model. A number of engineering parameters such as Concentration Index, Material Index, Density Gradient, and Stress Ratios are calculated. The seismic velocity values, engineering, consolidation, and strength parameters show that the bedrock at northern and southern parts of the study area is characterized by less competent rock quality, while the central part is characterized by more competent rock quality. Hence, the central part is suggested for construction activities.

Dynamic properties of the Quaternary sedimentary rocks and their influence on seismic site effects. Case study in Bucharest City, Romania

Bucharest is one of the cities most affected by earthquakes in Europe. Situated at 150–170 km distance from Vrancea epicentral zone, Bucharest had suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8–12 levels, while more than 150 old buildings with 6–9 levels were seriously damaged. The studies done after this earthquake had shown the importance of the surface geological structure upon ground motion parameters. New seismic measurements are performed in Bucharest area aiming at defining better elastic and dynamic properties of the shallow sedimentary rocks. Down-hole seismic measurements were performed in a number of 10 cased boreholes drilled in the Bucharest City area. Processing and interpretation of the data lead to the conclusion that shallow sedimentary rocks can be considered weak in the area, down to 150–200 m depth. Seismic wave velocity values and bulk density values presented in the paper associated with local geology are useful primary data in the seismic microzonation of Bucharest City. They are used as 1D models to derive transfer functions and response spectra for the stack of sedimentary rocks in several parts of Bucharest area, leading to a better knowledge of the local site amplification and associated frequency spectra. In a recent study the H/V spectral ratio using Nakamura’ s method was applied on the seismic noise measurements in 22 sites in Bucharest City in order to derive the fundamental period associated with these sites. The values confirm the previous results, showing a dominant resonance in the period range of 1.25–1.75 s. The fundamental periods obtained with Nakamura’ s method are in good agreement with those computed on the basis of geological and geotechnical data in boreholes, which show an increase of the fundamental period in the Bucharest area from south to north, in the same direction as the increase of the thickness of the Quaternary deposits above the Fratesti layer which is considered the bedrock in the area.

Bedrock detection and talus thickness assessment in the European Alps using geophysical methods

Three different geophysical techniques (ground-penetrating radar (GPR), 2D-resistivity, seismic refraction) were applied to measure sediment thickness of alpine talus slopes. The eight study areas covered a range of different rock types, aspects and elevations and are mainly situated in the north-eastern part of the European Alps. A total of more than 30 scree slopes were investigated. The emphasis was on the application of GPR. The other two methods were used additionally in five areas to verify the GPR results and to check the concurrence of the results. With all the techniques applied, certain difficulties of bedrock detection arose. GPR surveys using several frequencies seem to be the most powerful tool for detecting the bedrock surface and internal structures in these high-alpine environments. However, there frequently is no radar wave reflection at the debris–bedrock interface due to the rather similar dielectrical properties. This problem was overcome by using the characteristic reflection patterns of the subsurface units for delimitating debris from glacigenic sediments and bedrock. Typical radar facies are presented. The other two methods applied were impeded by the broad overlap between resistivity and seismic velocity values, respectively, of the subsurface layers. The widespread presence of compacted and/or glacigenic debris layers between surficial scree and bedrock rendered the interpretation difficult. The three methods coincide well in straightforward settings (e.g. debris superimposing bedrock). Additional sediment units like till, wet or compacted debris lead to considerable ambiguities and deviations between the results. Thus, the combined application of two or three techniques is strongly advisable to verify and improve the interpretation. The calculated Holocene rockwall retreat rates lay between 200 and 850 mm/ka which is well within the framework of previous measurements. The weathering rates at north faces seem to be roughly two times higher than at south faces in the areas of investigation.

Time-depth and velocity trend analysis of the Wasagu field

It is known in the North Sea basin that depths to major reflectors as determined from surface seismic data are often larger than the well depths. From this study of data sets from Wasagu field in the Niger Delta, it has been found that this statement might not hold in an area where rapid lateral variations in the subsurface (varying structural relief) cause big difference in bed velocities or where anisotropy is severe. From a combination of seismic data and checkshot data sets, which lie three wells, a relationship between seismic velocity and checkshot average velocity in Wasagu field, was derived. This relationship is the conversion factor that enables us to predict average velocity values from seismic velocity values. Using this factor, seismic times of a well have been converted to well depths. From well information alone, second degree polynomial fit has been used to convert seismic times of this virgin area to depth and from statistical analysis, it was discovered that the standard deviation of depth results got by causing the polynomial fit was 105.1ft and that obtained by using the conversion factor was 42.61ft. Nigerian Journal of Physics Vol. 16(2) 2004: 66-75

A seismic model of the lunar mantle and constraints on temperature and mineralogy

We determine seismic profiles of the Moon’s interior using travel times obtained from a re-analysis of the Apollo data. Due to the limited number of quakes and stations, travel times errors were determined and used in the inversions. Our model has a mean crustal thickness of about 30 km in the region of the Apollo network, with a 10 km zone of brecciation below the crust. Mean values of seismic velocities in the upper mantle are rather well constrained and are in the range 7.6–7.8 and 4.35–4.45 km s −1 for P and S waves, respectively. Velocity variations in the middle mantle are less well defined. In the zone of deep Moonquakes, below 740 km depth, velocities increase slightly to 8.15 ± 0.23 and 4.5 ± 0.10 km s −1 for P and S waves, respectively. We analyse the seismic profile in term of mineralogy and temperature constraints. Our preferred models are a pyroxenite model for the upper mantle and a magnesian-rich model for the lower mantle, with increasing # Mg with depth. We find temperatures of about 1100 K (elastic lithosphere limit) and 1500 K (thermal lithosphere limit) for radii of about 1400 and 1000 km, respectively, and show that the lunar mantle is probably depleted in Th and U by at least 70% compared to an Earth reference value of 25.7 ppb U. For a crustal thickness of 40 km with a mean 1010 ppb Th concentration,we then find bulk Th and U abundances comparable to, and possibly lower than currently accepted terrestrial values.

Imaging global chemical and thermal heterogeneity in the subcontinental lithospheric mantle with garnets and xenoliths: Geophysical implications

Suites of mantle-derived xenoliths in volcanic rocks provide estimates of the geothermal gradient and composition of the subcontinental lithospheric mantle (SCLM) at the time of the volcanic eruption. The development of single-grain thermometry and barometry, applied to xenocryst minerals in volcanic rocks, has greatly expanded the number of localities for which such data can be obtained and made it feasible to map the geology of the SCLM on a broader scale, both vertically and laterally. From garnet xenocrysts, it is possible to derive profiles showing mean values of olivine composition, bulk-rock composition, density and seismic velocities, as well as geotherm parameters and constraints on the thickness of the SCLM. Geochemical profiles, coupled with Re–Os dating of peridotites and their enclosed sulfide minerals, show that Archean or Proterozoic SCLM is preserved at shallow levels beneath many areas of younger tectonothermal age; this implies rapid vertical variations in Vs and Vp with depth, which may affect seismic interpretations. Data from several hundred localities worldwide define a secular evolution in the composition of the SCLM, related to the tectonothermal age of the overlying crust. Archean SCLM is typically strongly depleted in basaltic components, highly magnesian and thick (160–250 km), and has low geotherms; Phanerozoic SCLM is typically fertile (rich in basaltic components), Fe-rich, thin (50–100 km) and has a range of high geotherms; Proterozoic SCLM (much of which may be reworked Archean mantle) tends to be intermediate in all respects. The correlated variations in SCLM fertility, lithospheric thickness and geotherm reinforce the effects of each on seismic velocity, and produce more rapid lateral variations in seismic response than would result from thermal effects alone. These correlations are the key to using seismic tomography images to map the lateral extent of different types of SCLM.

The SCEC Southern California Reference Three-Dimensional Seismic Velocity Model Version 2

We describe Version 2 of the three-dimensional (3D) seismic velocity model of southern California developed by the Southern California Earthquake Center and designed to serve as a reference model for multidisciplinary research activities in the area. The model consists of detailed, rule-based representations of the major southern California basins (Los Angeles basin, Ventura basin, San Gabriel Valley, San Fernando Valley, Chino basin, San Bernardino Valley, and the Salton Trough), embedded in a 3D crust over a variable depth Moho. Outside of the basins, the model crust is based on regional tomographic results. The model Moho is represented by a surface with the depths determined by the receiver function technique. Shallow basin sediment velocities are constrained by geotechnical data. The model is implemented in a computer code that generates any specified 3D mesh of seismic velocity and density values. This parameterization is convenient to store, transfer, and update as new information and verification results become available.

Crack density and saturation rate in the 1995 Kobe Earthquake Region

We have estimated the 3‐D distribution of crack density parameter (ϵ) and saturation rate (ξ) in the 1995 Kobe earthquake region by applying a crack theory to values of seismic velocity and Poisson's ratio obtained from seismic tomography. Our results show that ϵ and ξ exhibit considerable heterogeneity. Higher ϵ and ξ exist in the Kobe fault zone, in particular, at the mainshock hypocenter. High ξ areas are generally consistent with high ϵ areas, but high ξ areas have a much wider distribution, indicating that microcracks exist in more localized areas, while fluids are permeating through wider areas in the crust. A significant discrepancy between ϵ and ξ exists beneath Osaka Bay where ϵ is low while ξ is high. ξ is generally high beneath seas but low beneath land areas. Osaka Bay and the present sea/land distribution in southwest Japan have existed for 2 millions years. This period is long enough for the sea water to permeate down to the deep crust through the active faults that would have been ruptured during many earthquakes cycles.

Predicting Abnormal Reservoir Pressures using offset Dependent Reflectivity: Theoretical Considerations

The concept of using amplitude variations with offset (AVO) for the direct detection of hydrocarbons was introduced to the oil and gas industry in the early eighties. In the late eighties Rutherford and Williams proposed a model representing different classes in normally pressured gas sand formations. In this paper, a model for the AVO response for overpressured clastic formations is proposed based on the rationale that abnormally high pore fluid pressure leaves its own pronounced effects on clastic formations: such as abrupt increase in porosities, decrease in interval velocities, high fluid content, and lower bulk densities. The implication is that overpressured formations should show a different trend for AVO response compared to normally pressured formations. The AVO response in overpressured formation was modeled using both synthetic well data representing an overpressured sandstone and also typical values of seismic velocities reported from overpressured formations. The results suggest that a characteristic polarity reversal from negative to positive reflection coefficients can be observed as the offset increases.

P-SHconversions in a flat-layered medium with anisotropy of arbitrary orientation

SUMMARY P-SH conversion is commonly observed in teleseismic P waves, and is often attributed to dipping interfaces beneath the receiver. Our modelling suggests an alternative explanation in terms of flat-layered anisotropy. We use reflectivity techniques to compute three-component synthetic seismograms in a 1-D anisotropic layered medium. For each layer of the medium, we prescribe values of seismic velocities and hexagonally symmetric anisotropy about a common symmetry axis of arbitrary orientation. A compressional wave in an anisotropic velocity structure suffers conversion to both SV-and SH-polarized shear waves, unless the axis of symmetry is everywhere vertical or the wave travels parallel to all symmetry axes. The P-SV conversion forms the basis of the widely used ‘receiver function’ technique. The P-SH conversion occurs at interfaces where one or both layers are anisotropic. A tilted axis of symmetry and a dipping interface in isotropic media produce similar amplitudes of both direct (P) and converted (Ps) phases, leaving the backazimuth variation of the P-Ps delay as the main discriminant. Seismic anisotropy with a tilted symmetry axis leads to complex synthetic seismograms in velocity models composed of just a few flat homogeneous layers. It is possible therefore to model observations of P coda with prominent transverse components with relatively simple 1-D velocity structures. Successful retrieval of salient model characteristics appears possible using multiple realizations of a genetic-algorithm (GA) inversion of P coda from several backazimuths. Using GA inversion, we determine that six P coda recorded at station ARU in central Russia are consistent with models that possess strong (> 10 per cent) anisotropy in the top 5 km and between 30 and 43 km depth. The symmetry axes are tilted, and appear aligned with the seismic anisotropy orientation in the mantle under ARU suggested by SKS splitting.

Assessment of geomechanical characterization of a rock mass using a seismic geophysical technique

In this article the use of the seismic properties of a rock mass to assess the geomechanical behaviour of the rock mass is examined and illustrated. The correlation between the values of seismic velocity and some basic parameters of rock mechanics, such as RQD and fracture frequency, have been established. Moreover, the relationships between the engineering rock-mass classification systems and seismic quality index (QI) have also been derived. The relationships have been derived from an investigation for a proposed dam in Wadi Mujib, Jordan. The ground conditions comprise colluvial and fluvial superficial deposits overlying limestones, mudstones, marls and shales. It is suggested that the relationships obtained in this study could be applied in areas that have similar lithological and structural characteristics.

Phase transformations in the earth's mantle and subducting slabs: Implications for their compositions, seismic velocity and density structures and dynamics

Abstract Phase transformations in model mantle compositions and those in subducting slabs have been reviewed to a depth of 800 km on the basis of recent high‐pressure experimental data. Seismic velocity and density profiles in these compositions have also been calculated using these and other mineral physics data. The nature of the seismic velocity and density profiles calculated for a pyrolite composition was found to generally agree with those determined by seismic observations (e.g. PREM). The locations of the seismic discontinuities at 400 and 670 km correspond almost exactly to the depths where the transformations of the olivine component to denser phases take place. Moreover, the steep gradients in the seismic velocity/density profiles observed between these depths are qualitatively consistent with those expected from the successive transformations in the complementary pyroxene‐garnet component in the pyrolite composition. Further, the calculated seismic velocity and density values agree well with those observed in the upper mantle and mantle transition region within the uncertainties attached to these calculations and observations. Pyrolite or peridotite compositions are thus most likely to represent the composition of the mantle above 670 km depth, although some degrees of chemical heterogeneity may exist in the transition region. The observed sharp discontinuous increases of seismic velocities and density at this depth may be attributed either to the phase transformation to a perovskite‐bearing assemblage in pyrolite or to chemical composition changes. Density profiles in subducted slabs have been calculated along adequate geotherms assuming that the slabs are composed of the former oceanic crust underlain by a thicker harzburgitic layer. It is shown that the former oceanic crust is substantially less dense than the surrounding pyrolite mantle at depths below 670 km, while it is denser than pyrolite in the upper mantle and the transition region. The subducted former oceanic crust may be trapped in this region, forming a geochemically enriched layer at the upper mantle‐lower mantle boundary. Thick and cool slabs may penetrate into the lower mantle, but the chemically derived buoyancy may result in strong deformation and formation of megalith structures around the 670 km seismic discontinuity. These structures are consistent with those detected by recent seismic tomography studies for subduction zones.

On Poisson's ratio and composition of the Earth's lower mantle

Poisson's ratio of the lower mantle, calculated from recently published values of seismic wave velocities and extrapolated to atmospheric pressure and room temperature is found to be in the range 0.23 ⩽ ν ⩽ 0.25. These values are compared with the values of Poisson's ratio calculated for binary mixtures of MgSiO 3 perovskite and magnesiowüstite with various iron contents. Current values of the experimental error on measured elastic moduli give little hope to be able to discriminate between pyrolite and chondritic lower mantles: both are acceptable if the shear modulus of perovskite is in the upper range of Liebermann et al. estimates. A similar calculation using the seismic parameter φ confirms the results obtained by considering Poisson's ratio and further constrains the value of the shear modulus of perovskite to lie between 1600 and 1700 kilobars for current mantle models to remain plausible. Chemical stratification of the mantle is, therefore, possible but not required by seismological data.

The miocene Great Basin of Western North America as an extending back-arc region

A narrow continental volcanic arc has lain near the western margin of the North American continent since mid-Miocene time. Its south end began retreating northward 18 m.y. ago. The active remnant of this andesitic arc today is the Cascade Range of Oregon, Washington, and British Columbia. A large part of the Great Basin and region to its north was situated throughout this period first wholly, then partially, in a back-arc position relative to the arc. This region had, and still has, most of the characteristics of back-arc regions elsewhere in the world—a thinned, faulted and extended crust and lithosphere, limited development of a geophysical bilateral symmetry (a mid-to-late-Miocene symmetry axis is marked by narrow swarms of basaltic dikes with associated positive linear magnetic anomalies that are parallel to the contemporary trench), high heat flow, low Bouguer gravity and seismic wave velocity values, notable seismic attenuation in the mantle, and a fault plane solution record dominated by normal-fault mechanisms. This back-arc region differs somewhat from most others (those composed of oceanic crust) because of its continental setting and recent geologic history. Despite its name, the Great Basin stands high, nearly 2 km above sea level. This high elevation owes, in part, to the fact that extension and heating of the continental lithosphere are still underway, though not as a back-arc phenomenon. The present lithospheric stretching results from oblique extension near the transform boundary of the North American plate, the San Andreas fault system. The latest stretching has probably maintained the physical state of the lithosphere first developed during back-arc spreading.

Velocity anisotropy in a mantle peridotite from the Ivrea Zone: Application to upper mantle anisotropy

Compressional (P) velocity anisotropy to 1.5 kbar at room temperature in a Iherzolite from the Lanzo massif in the Italian Alps was measured. These studies are relevant to the origin of the velocity anisotropy in the oceanic upper mantle. The results show the following. (1) The velocity anisotropy of the sample is about 7% and is independent of pressure to several kilobars. The anisotropy of the sample is referred to its in situ (field) orientation. (2) The seismic velocities were measured in three mutually orthogonal directions related to the field structures (foliation and lineation), and thus a means of estimating the velocity anisotropy in these peridotite massifs directly from the field structural data is provided. The field structures, in turn, are closely related to the fabrics and to the flow directions. (3) The anisotropy of the sample calculated from the fabric data is in good agreement with the measured anisotropy. The anisotropy of the Lanzo massif is calculated from several hundred field measurements of foliation and lineation referred to the measured anisotropy of the sample along those structural directions. (4) The results show that the laboratory measurements on the Iherzolite sample are similar to the values of density and seismic velocity of the Ivrea body shown in the geophysical model; however, the present results predict a seismic velocity anisptropy for the Lanzo massif, the maximum velocity trending NNE-SSW and the minimum velocity trending WNW-ESE. (5) These results support the interpretation of seismic anisotropy in the oceanic upper mantle essentially as given by Francis.

Recent Advances in Geophysics: ABSTRACT

Exploration geophysics has been advancing by the increasing production of geologic information. That is, more physical parameters of the stratigraphic column are being measured to finer resolution. In seismic prospecting, continuous determination of seismic wave velocity is beginning to be used routinely while attenuation measurements are being made experimentally. Binary-gain digital recording with 24- and 48-fold multiplicity is proving necessary for these measurements. At sea, magnetic, gravimetric, and other surveys are being conducted concurrently with seismic surveys. In some areas, if detailed reflection data are combined with seismic velocity and attenuation values and supplemented with detailed gravity and magnetic measurements, the local stratigraphy and lithology can be uniquely defined. Field techniques of transport and navigation have improved markedly so that useful results can be obtained almost anywhere in the world and the results can be displayed on maps that are consistent on a worldwide basis. End_of_Article - Last_Page 868------------

Features of Sedimentary Cover of Arctic Ocean: ABSTRACT

1. The part of the earth's crust surrounded by three large pre-Paleozoic platforms (the eastern European, middle Siberian, and Greenland-Canadian) is the Arctic basin, and the presence of these 3 platforms was the initial basis for the origin and development of the Arctic Ocean. The existence of these platforms and their surrounding fold belts created conditions favorable for sedimentary accumulation in the inner regions of the ocean. 2. The various sedimentary frameworks in different parts of the ocean show the different types of tectonic movements that affected the area, and indicate specifically the history of reconstruction of the former continental features into oceanic ones. 3. Oceanic margins--the regions of the present shelf--represent, according to tectonic data, vast parageosynclinal basins nearly of isometric shape, composed of thick sedimentary layers of different ages and structures. In a west-east direction one may observe the successive rejuvenation of the sedimentary cover and the progressive decrease in the degree of consolidation of the cover sediments. 4. The sedimentary framework of the eastern sector of the inner Arctic Ocean basin differs from that of the western sector. A double stage structure of the sedimentary sequence is typical for the eastern sector of the Arctic Ocean basin. Unconsolidated sediments with seismic velocity values of 1.6-2.5 km/sec are everywhere underlain by consolidated rocks with velocity values of about 3.5-4.5 km/sec. In the western Arctic basin, the unconsolidated sediments overlie either relict folded basement with seismic velocity values of 5.0-6.0 km/sec, or basaltic basement with seismic velocity values of 6.3-6.7 km/sec. 5. In large arched uplifts, the thickness of unconsolidated End_Page 2476------------------------------ sediments is much less than that in the adjacent troughs, but in most places, the thickness of the rocks comprising the second stage is identical for both troughs and orogenically uplifted areas. The last fact suggests that the large vertical movements of the inner Arctic Ocean occurred mainly in late Mesozoic-Cenozoic time. It was during this time that the present morphometric form of the Arctic Ocean basin was created. End_of_Article - Last_Page 2477------------

Portable Refraction Seismography Survey of Gold Placer Areas Near Nome, Alaska: ABSTRACT

A seismic refraction study of the beach and tundra gold placer areas near Nome, Alaska, was made using a small, light-weight, portable seismograph during the summer of 1967. Geophone configuration and type of energy source were determined during a preliminary experimental survey. Because the beach study was successful, a short experimental seismic line was completed inland to determine the usefulness of a portable refraction seismograph in permafrost areas near Nome. Basic problems in permafrost areas are the high seismic velocities in the overburden, caused by increase in elastic modules in frozen ground, and the acoustical absorption and variable thickness of the overlying tundra. The increase in sediment velocity reduces the possibility that there is a marked velocity contrast at the bedrock-overburden interface, and the organic material of the tundra absorbs returning seismic energy. These problems were reduced by detonating the explosive energy source on the permafrost surface and by placing the geophones in the thaw zone of silt beneath the spongelike ma ter of the tundra. The beach survey results indicated that internal stratigraphy of the overburden could be interpreted and seismic velocities assigned to the different units. A very low-velocity, dry to damp layer of Holocene sands covering most of the beach has seismic velocity values of 0.15-0.73 km/sec. In other low-velocity layers included in the overburden, and especially conspicuous near river mouths, velocity values range from 0.62 to 1.00 km/sec. A poorly consolidated nearshore or estuarine silt, clay, and sand layer of Sangamon age (late Pleistocene) with velocity values of 1.20-1.80 km/sec is below the very low-velocity layer. Beneath the estuarine material is a till of Illinoisan age (middle Pleistocene) that has a velocity of 2.80-4.00 km/sec. Bedrock was well defined in all seismograms and exhibited velocity values from 4.20 to 5.60 km/sec. A basement contour map of the beach was constructed from depth data obtained along the beach with the refraction seismograph, from offshore seismic-reflection data, and from onshore drillhole information. Several buried channels were identified which may be sites of possible gold placer deposits. Beneath the tundra a bedrock surface dips under Dry Creek from both sides, and a bedrock contour map was drawn from refraction-seismograph data and drillhole information. Results of the Nome tundra survey illustrate the feasibility of the portable seismograph as a placer prospecting tool for use in tundra-permafrost areas. End_of_Article - Last_Page 471------------

PROBABILITY STUDIES IN THREE VARIANTS: SEISMIC VELOCITY, DEPTH, AND LITHOLOGY

In an effort to determine if lithology—shales, sands, or a mixture of both—can be inferred from interval seismic velocity values, probability theories of statistical inference were applied to data from 16 wells shot for velocity information and from electric logs of the wells in the San Joaquin Valley, California, area. Average velocities, velocity functions, and probability ratios were derived for the three classes of lithology, for all data, for the two general areas, and for three individual oil fields: Wasco, Rio Bravo, and Coalinga.

General and Engineering Geology of Sekigahara Tunnel, Shin-okaido Line

In planning of Sekigahara tunnel, 2809m long and situated in a disturbed area of Palaeozoic rocks at the midst Of Nagoya and Kyoto, a series of careful investigation (including borings and seismic prospectings) was made adequately and construction schedule was based closely on geological considerations. Seeing back from the actual results of driving, many faults and breccia zones were forecasted properly, and except several small troubles due to swelling of clay in altered slate, almost all the works have successfully been completed to;the end of this year.Various data, such as obtained values of seismic velocity, kind of rocks, both infered and encountered, and thickness of lining concrete planned and adopted, are summarized in Fig.2.