High pressure and temperature in the earth's crust lead to fracture and microcracks in rocks. Direct access to earth crust rocks at great depths is very costly and, in most cases, impossible. The study of the condition of rocks at great depths is often done using indirect methods such as seismic WAVEs. The results of these studies are compared with the results of laboratory studies of WAVE velocities in different rocks and the conditions of the rocks are simulated. At high depths, hydrostatic stress is applied to the rocks of the earth's crust, and tectonic, earthquake and other stresses cause it to be anisotropic. The primary purpose of this study is to investigate the change in compressive WAVE VELOCITY due to the change in compressive stress in rocks. At first, a cylindrical core of different stones with a length to diameter ratio of 2 to 2. 5 is prepared according to the standard test method (ASTM D4543) and their dimensions and weight are determined. after measuring the unconfined compressive strength of cores according to the standard test method (ASTM D2938), the hydrostatic pressure of 50% to 95% of it is applied to the rock samples prepared from the earth. This pressure is applied to the cores by using the Hoek cell (for lateral pressure) and the axial load machine and using an ultrasonic device, determine the compressive WAVE VELOCITY (ultrasonic pulse) is determined according to the standard test method (ASTM D2845) in the axial direction of the sample. Then, the WAVE VELOCITY was measured by decreasing the lateral pressure (increasing deviatoric stress) in a stepwise manner and the WAVE VELOCITY was measured at each step. In the following, comparative diagrams of compressive WAVE VELOCITY (Vp) with density (ρ, d), uniaxial compressive strength (UCS) and the effect of hydrostatic stress (σ, hyd) and deviatoric stress (σ, dev) on P-WAVE VELOCITY in each sample are drawn. The results show linear relationships between compressive WAVE VELOCITY and the physical properties of rock samples. Also, the PWAVE VELOCITY at hydrostatic pressure is the highest and as the lateral pressure decreases (increasing the deviatoric stress), the VELOCITY also decreases.

Seismic WAVE propagation in surficial stratified soil and deep rock is studied in many engineering fields like Geotechnical earthquake engineering, Geophysics and seismology. Seismic WAVEs might be generated by a significant seismic event, volume collapse in earth’ s mantle, chemical or nuclear explosions and surface impact sources. Although the seismic WAVEs’ path in soil layers may be shorter than their path in bedrock, they are influenced significantly by the mechanical properties of surficial soil layers. Soil layers may be saturated or not fully-saturated by a single fluid, which is known as unsaturated soil. Seismic WAVEs generated at the source are known to be body WAVEs of two categories (a) COMPRESSIONAL WAVE (P-WAVE), (b) shear WAVE (S-WAVE). In spite of the abundance and deepness of theoretical analyses, experimental results on measuring the COMPRESSIONAL WAVEs in unsaturated soils and rocks are inadequate and mainly have focused on the relation between first COMPRESSIONAL WAVE VELOCITY and degree of saturation instead of suction. Furthermore, the experiments focus on the specimens of sandy soils and rocks with a series of repeated experiments in various degree of saturation conditions. This paper presents the results of three series of ultrasonic tests carried out on fine grained soils. The soils chosen for experimental study are three commercial kaolin named ZK1, ZK2, and ZK3, from Zenoz mine in northwest Iran. These materials have plasticity index (IP) of 9%, 15%, and 19%, and classified as lean clay (CL), silt (ML), and elastic silt (MH) respectively according to Unified Soil Classification System. 15 specimens were compacted at different initial water contents and void ratios and subsequently allowed to dry gradually until air-dry. cylindrical samples, 50 mm in diameter and 100 mm high, were prepared in a mold by compacting a soil – distilled water mixture at proctor optimum dry density and another four points of standard proctor compaction curves; two at 0. 5 kN/m3 less than optimum dry density in both dry and wet side of optimum water content point and two at 1 kN/m3 less than optimum dry density in dry and wet side of optimum water content point. All samples were compacted in seven layers using the under-compaction technique to ensure specimen homogeneity along the height. Measurements of COMPRESSIONAL WAVE VELOCITY (Vp) (using ultrasonic) and matrix suction (using the filter paper technique), together with water content, were made at various stages during the drying process (4 times for each specimens; at the time of making the sample and after 4, 8, and 16 hours). The results of the tests suggest that, as a soil dries, its COMPRESSIONAL WAVE VELOCITY increases with increasing in suction. The results imply that in prediction of COMPRESSIONAL WAVE VELOCITY the effectiveness of void ratio must be considered as well as the suction effects. Both COMPRESSIONAL WAVE VELOCITY (Vp) and the corresponding suction (s), have been shown to vary in consist and predictable manner as a function of the initial void ratio at compaction state (ecomp), the suction and the soil’ s plasticity index (PI). Thus, an empirical expression was developed which permits estimation of the value of COMPRESSIONAL WAVE VELOCITY, Vp of compacted fine grained soils subject to drying at the suction and material properties expected in prototype conditions.

In this research the porosity of Shurijeh formation in northeast of Iran is measured from neutron and density logs in the well GL2. Then we measured COMPRESSIONAL WAVE VELOCITY from acoustic log, and the clay content from geology log. With the data of clay content, porosity and COMPRESSIONAL WAVE VELOCITY we found a linear relationship between these parameters as follows: Vp =5.55- 9.62Æ-1.37C    R2 = 0.86 where Vp, Æ and C are respectively the VELOCITY of saturated sandstone (in km/s), porosity and clay content (both in fractional volume). Based on the above relationship, if Vp calculated from sonic log and with the knowledge of the clay content, them the porosity of the formation could be estimated.

WAVE VELOCITY and attenuation are among the most important attributes of stress WAVEs that propagate through geomaterials. Utilizing these attributes, it is possible to acquire useful information about porous geomaterials such as soil and rock and also the fluids that saturate the pores of geomaterials. The key point in order to gain these informations is to establish an accurate link between field measurements of WAVE attributes and physical properties of geomaterials’ skeleton and pore fluid. The pore fluids and their inhomogeneous distribution fluid are among factors that affect WAVE VELOCITY and attenuation to a considerable extent. Patchy saturation of pores which occurs on the scale larger than grians size but smaller than WAVElength is one of the reasons that causes inhomogeneity in pore fluid distirbution. The influence of such inhomogeneity is studied in present paper. Two different attenuation mechanisms including relative movement of fluid with respect to solid phase and also attenuation caused by grain to grain contact are implemented to fully assess WAVE attenuation. It is observed that the former attenuation is more dominant at higher frequencies compared to the latter attenuation.

COMPRESSIONAL and shear WAVE velocities (Vp and Vs respectively) are basic and essential parameters for any geomechanical modelling in deep ground conditions. However, both are complex parameters that are strongly influenced by other rock properties such as porosity, in situ stress, pore filling, clay content, etc. Therefore, detailed information about the contribution of each of these attributes can improve the results obtained in geomechanical models. Especially when the WAVE VELOCITY in the surface conditions is estimated based on in situ data such as geophysical logs from wells or core samples or drilling chips, the importance of this matter becomes much significant. In this research, experimental data for more than 180 shaly rock samples were analysed. Clearly, porosity was the most critical parameter affecting shear WAVE VELOCITY. Accordingly, increasing porosity leads to a dramatic decrease in WAVE VELOCITY. Nevertheless, it was noticed that for a certain porosity value, a relatively wide range of WAVE velocities may be observed. Further investigation revealed that, clay content was also a significant contributing parameter. Based on explicit statistical analysis, a predictive equation was introduced with which shear WAVE VELOCITY can be estimated with high certainty. Accordingly, for samples with the same porosity, variation in clay content would result in different WAVE velocities

Stress WAVEs contain useful information about the properties of porous materials; they can be recovered through different non-destructive testing methods such as crosswell, vertical seismic profile, borehole logging as well as sonic tests. In all these methods, it is crucial to assess the effects of frequency on WAVE attributes including VELOCITY and intrinsic attenuation. The dependency of permeability on frequency which is known as dynamic permeability and its effects on WAVE attributes of COMPRESSIONAL WAVEs are investigated in the present paper. Utilizing the dispersion relation derived for COMPRESSIONAL WAVEs, it is shown how the VELOCITY and intrinsic attenuation of WAVEs propagated in water saturated sand may be influenced by dynamic permeability. In low frequency range (viscous dominated flow regime), the dynamic permeability behaves like Darcy steady-state permeability and its effects on WAVE attributes are negligible. However, deviations from Darcy permeability start to occur at higher frequencies. Therefore, it is important to know how dynamic permeability controls the behavior of WAVE VELOCITY and intrinsic attenuation in relatively high frequencies. For example, it is demonstrated that neglecting dynamic permeability results in overestimation of velocities of fast and slow WAVEs in high frequency ranges (inertia dominated flow regime).

Distinguishable amplitude phenomena on surface seismic data often resulted from contrasts in the elastic parameters of subsurface layers. Various techniques have been involved to analyze and highlight such phenomena for their potential use as "Direct Hydrocarbon Indicator (DHI)". More recently, other techniques have been developed based on the variation of reflection coefficient with angle of incidence, conventionally called Amplitude-Versus-Offset (AVO).During the last twenty years the significance of AVO analysis for studying seismic reflection in oil exploration has been considered more importantly. In this work, first, a seismic line from a gas field and also a well are selected to indicate the results of the application of AVO analysis for detection of hydrocarbon reservoir in this field.In this project, using well logs and information obtained by core analysis, a synthetic seismogram has been built applying Zoeppritz equation. And Using Hampson-Russell software, AVO attributes have been extracted from synthetic seismogram. Then anomalies of these attributes have been investigated and compared with the anomalies from AVO attributes which were extracted from real seismic data to characterize the reservoir.It has been seen that the extracted attributes of the synthetic seismogram confirm the anomalies from real seismic data. Finally according to the obtained result, observed anomalies can be interpreted as a Gas Cap for this reservoir. This study is useful to identify reservoir and nonreservoirs and the results of this study are considered as input for detailed reservoir studies. In particular, knowing the reservoir physical and saturating fluid properties is of great importance in making plans for developing the reservoir.

Shear WAVE VELOCITY provides petroleum engineers with the valuable information to manage efficient processes in the development of hydrocarbon reservoirs. Shear WAVE VELOCITY (Vs) plays a prominent role in characterizing some important reservoir properties such as lithology, pore fluid type, productive zone, etc. Since using well logging is too expensive, Vs is not available in all wells. In this case, a wide variety of empirical relationships have been published for different lithologies in which Castagna and Greenberg are of the first rank. Greenberg and Castagna (1993) have given empirical relationships in multiminerslic, brine-saturated rocks based on representative polynomial regression coefficients for pure lithologies represented by Castagna. In addition, Gassman relationships should be applied to fulfill assumption of brine saturation. The present study carried out in an Asmari reservoir of an oil field in Sothwest Iran which has a Vs log. In the present paper, firstly, Gassman relationships are applied to replace the common fluid. So COMPRESSIONAL WAVE VELOCITY (Vp) is calculated in the condition of brine saturation. Note that, Greenberg-Castagna relationships are empirical and should be modified for the studied reservoir. This modification done in two different phases due to lithology and water saturation. Finally, regression coefficients of Castagna used for prediction of Vs in limestone and shale. Also, regression coefficients of first and second modifications are respectively used for dolomite and sandstone to predict the Vs. According to results, correlation coefficients between real and predicted values are 0.84 and 0.94 respectively before and after modification, which prove the superiority of modified model of Greenberg-Castagna.

The purpose of this study is to estimate COMPRESSIONAL and shear WAVE quality factors of seismic WAVEs by using local earthquakes occurred in the NW of Iranian Plateau. In seismological engineering studies, quality factor estimation of body and shear WAVEs plays an important role in seismic risk assessment of different areas, determining the exact magnitude of the earthquake, strong ground motion simulation and study of destructive energy of earthquake from near to intermediate region. In this study, earthquakes recorded in the Iranian Seismological Center (IRSC) and Iranian National Broadband Seismic Network (INSN) for the longitudinal band from 43° E to 53° E and the latitude band from 36° N to 40° N were used. Among the 17 stations, 14 stations belong to the IRSC and the rest belong to the INSN. Due to the presence of some big cities in the northwestern part of Iranian Plateau, quality factors of body and shear WAVEs were estimated by using the data of 17 seismological stations including 13000 recorded earthquakes of the IRSC and INSN. This region of intense deformation is situated between two thrust belts of the Caucasus to the north and the Zagros Mountains to the south. The NW of Iranian Plateau is a part of Turkish– Iranian plateau and includes historical and destructive earthquakes and two volcanoes with lots of thermal springs around. The North Tabriz Fault (NTF) is one of the active faults in NW Iran that has a clear surface expression. Seismic quiescence and large historical earthquakes in the region in more than the two last centuries have increased the seismic risk of this region. To estimate seismic hazard in an area, a two-step process is needed. First, we must understand the nature of the earthquake sources that generate potentially hazardous ground motion. This includes knowledge of the distribution of seismic source zones, predominant fault mechanisms and return times of large events. Second, we must understand the effects of the transmitting medium (the Earth) on the seismic WAVEs. A synthesis of the source and path effects will allow us to calculate the ground motion at a given site. Seismic attenuation is also caused by intrinsic mechanisms that convert the WAVE energy to heat through friction, viscosity, and thermal relaxation processes. Scattering redistributes WAVE energy within the medium but does not remove energy from the overall WAVEfield. In contrast, intrinsic attenuation mechanisms convert the WAVE energy to heat through friction, viscosity, and thermal relaxation processes. Energy loss caused by inelastic behavior is called inherent or internal attenuation and is determined by the inverse of the Q parameter. Large values of quality factor mean that attenuation is low and when Q is equal to zero, attenuation is very high. Aki (1980) used the normalized Coda for the first time in order to estimate absorption amplitude of the S WAVEs. Since then, this method has frequently been used in seismological studies for estimation of the absorption parameters of seismic WAVEs (see, for example, Yoshimoto, 1993; Hatzidimitriou, 1995). For three categories of data with epicentral distances less than 100 km, from 100 to 200 km and 0 to 200 km, attenuation variation investigation of body WAVEs was carried out in 9 frequency bands with central frequencies of 3, 5, 7, 10, 14, 20, 28, 38 and 47 Hz and the quality factor was estimated in different frequencies for each station, separately. For the northwesern part of Iran, the frequency dependence of the body and shear WAVE quality factors in all stations were estimated so that their average values are quantified as Qp=55f 0. 84 and Qs=38f 0. 93, respectively. Due to the low values of the Q parameter and thus high attenuation values of body and shear WAVEs in North West of Iranian Plateau, the amplitude of the propagated WAVEs are decreased severely in the interested area when these WAVEs pass through it. The attenuation effect of seismic WAVEs would reduce the damages caused by the earthquakes at appropriate distances from the faults at the time of probable earthquake occurence.