جستجوی مقالات مرتبط با کلیدواژه « جهت یافتگی » در نشریات گروه « زمین شناسی »

Discontinuities are the most important property of rock mass that control the permeability. Effects of orientation, frequency and number of sets of discontinuities on the permeability investigated before and after improvement by grouting using cement grout in this study. Rock samples having one, two and three cross-sets of single discontinuities and three cross-sets of discontinuities with one set having four parallel discontinuities, in different groups of various orientations (angle between planes of discontinuities and horizontal direction) of 0, 30, 45, 60 and 90 degrees in total of 20 different groups that have been preparing. The permeability of 20 group samples with different orientation, frequency and number of set of discontinuities has been measured. Discontinuities of multiple groups of samples using cement grout improved and also their permeability measured. The results show that the effect of discontinuities’s orientation on permeability changes by changing the number sets and the frequency of discontinuities. In samples having three cross-sets of perpendicular discontinuities with one set having four parallel discontinuities which have been represented jointed rock mass. Permeability is mainly affected by the orientation of the set that has four parallel discontinuities. Orientation, frequency and number of sets of discontinuities cause change in permeability about 759048 times. The permeability reduces in the range of 9-99% with the improvement of samples using cement grout injection. This indicates that the orientation, frequency and number of sets of discontinuities are very effective in reducing permeability by the injection.

Recent progress in seismology has demonstrated that empirical Green’s functions (EGFs) of inter-station distances can be extracted using cross correlation of ambient seismic noise recorded in the similar time at two stations (Weaver and Lobkis، 2002; Shapiro and Compillo، 2004; Wapenaar، 2004). Consequently، this method provides a great set of data even in low seismicity regions to apply in the tomographic studies. Thus، the resulted tomographic images using the ambient seismic noise method (hereafter ANT) can show interior earth structures with a higher resolution compared to classical tomography methods (Shapiro et al، 2005; Lin et al.، 2007; Shirzad et al، 2013). Diffused signals are the main assumption in the ANT method (Snider، 2004). Ambient seismic noise sources generate a coherent and transient noise wavefield with random amplitude and phase in a medium (Van-Tighelen، 2003; Gorin et al.، 2006). Reconstruction of the propagating path information using the amplitude of the recorded noise wavefield is impossible، but coherent information provided by propagating path can be extracted using cross correlation of long time ambient seismic noise recorded (Weaver and Lobkis، 2004; Gorin et al.، 2006). This coherent information is called elastic response of medium or empirical Green’s functions (Shapiro and Compillo، 2004; Roux et al.، 2005; Sabra et al.، 2005). Generally، the ambient seismic noise recorded for each station is composed of surface waves (Rayleigh and Love) with random amplitude and phase (Aki and Richards، 1980). Cross correlation function of these data will be symmetric if the ambient seismic noise wavefields generated by random sources are distributed uniformly (Snider، 2004). Earth structures can be studied using travel-time of extracted EGFs such as Rayleigh wave fundamental mode (Shapiro et al.، 2005). Some studies (e. g. Stehly et al.، 2006; Pedersen et al.، 2007) indicate that the inhomogeneous distribution of the signal energy in various azimuths، which results in directionality of ambient seismic noise، produces deviation in tomography results and causes incorrect interpretations. Consequently، optimization of extracted tomographic maps based on the ANT method needs comprehensive knowledge of spatial and seasonal distribution of the noise wavefield in study areas (Stehly et al.، 2006; Pedersen et al، 2007). Gutenberg (1936) suggested that the sources of primary and secondary oceanic microseisms observed throughout the Europe are located in the northeastern Atlantic Ocean. Primary and secondary microseisms dominate the noise wavefield in certain frequency ranges. The interaction between the swell and the sea bottom generates the primary microseisms which are dominated by periods of 12–25 s. Also، interfering water wavefield components travelling in opposite directions generate the secondary microseisms which are dominated by periods of 5-10 s (Gutenberg، 1936). In this study، we analyzed three-component recordings of continuous data from 30 stations in the Central Alborz region depicted in Figure 1. The Alborz Mountain range in the southern margin of the Caspian Sea is a part of the Alpine–Himalayan orogenic belt. The Alborz Mountain range resulted from a stress state derived from the horizontal compressive forces of the Central Iran Plateau has been induced by the collision of the Arabian plateau and the Asian continent (Berberian and King، 1981; Zanchi et al.، 2006). The dataset used in this study consisted of 10 digital accelerometers with CMG-5TD sensors operated by the Tehran Disaster Mitigation and Management Organization (TDMMO)، 18 digital narrow-band seismometers with SS1 seismometer sensors (corner frequency ≥1 Hz) operated by the Iranian Seismological Center (IRSC) at the University of Tehran، and two digital broadband instruments with a CMG-3T sensor operated by the International Institute of Earthquake Engineering and Seismology (IIEES). For the TDMMO acceleration network، the IRSC and the IIEES seismic networks continuous data from 2010 were analyzed. In the case of azimuthal distribution of the ambient noise، normalized amplitude of the cross-correlations versus azimuth (rose-diagram) constrained the direction to the sources of the ambient seismic noise، based on all available station-pairs. The average fractions (the number of Love/Rayleigh path with a SNR>10 in a given 20° azimuthal bin was normalized to the total number of Love/Rayleigh paths in that given bin) of the Love and Rayleigh yearly empirical Green’s functions with a SNR>10 were in the orders of 0. 78 and 0. 73، respectively، at the period band of 1–10 s. Our final results indicated that the average fractions per cent of Love and Rayleigh paths with SNR>10 were above 68% and 64% on a yearly scale، and never decreased to 45% and 50% on a monthly scale at the period band of 1-10 s، respectively.