Τα διαθέσιμα δεδομένα που αφορούν την κατακόρυφη διάταξη επιταχυνσιογράφων της Πάτρας (VA-1) περιλαμβάνουν περισσότερες από 1000 σεισμικές καταγραφές καθώς και στοιχεία για την, σχετικά σύνθετη, στρωματογραφία και την κατανομή VS–βάθος στη θέση της εγκατάστασης. Στην παρούσα Διατριβή υπολογίζονται οι (εμπειρικές) συναρτήσεις μεταφοράς της κίνησης στις στάθμες των υπογείων οργάνων και εκτιμώνται τα χαρακτηριστικά εδαφικής απόκρισης (δεσπόζουσες περίοδοι και ενίσχυση). Διαπιστώνεται ότι οι φασματικοί λόγοι H/V των επιφανειακών καταγραφών παρέχουν τη δυνατότητα της αποτελεσματικής αναγνώρισης των καταγραμμένων χαρακτηριστικών της κίνησης. / The available data from the Patras accelerograph vertical array (VA-1) include more than a thousand of seismic recordings as well as information on the relatively complex soil stratigraphy and distribution of VS vs depth at the location of installation. In this Thesis the (empirical) transfer functions of motion at the levels of underground instruments are estimated and the characteristics of soil response (dominant periods and amplification) are assessed. It is found that the calculated spectral ratios H/V of seismic recordings at the ground surface can provide an efficient tool for identification of the recorded motion characteristics.

Acquisition and interpretation of 3-D seismic data led DeAngelo and Hardage (2001) to describe the channel system in the south central Cut Bank area in Glacier County, Montana. The presence of a low velocity layer called Bentonite was also discovered in the area with the help of well-logs. Bentonite is a volcanic ash, which lies on both sides of the channel system and is absent within the channel. DeAngelo and Hardage (2001) shot a vertical seismic profiling (VSP) survey at well # 54-8 to analyze the formation structure in depth, since seismic signals around the reservoir area were unclear in the 3-D survey. This research attempts to estimate the attenuation properties of the Bentonite layer in the Cut Bank oil field. VSP data is processed for velocity information and estimation of seismic Q using the spectral ratios method (SRM). The SRM theoretically assumes that the propagating signal is a plane seismic wave traveling vertically from one point to another in a homogeneous model. The amplitudes at the start and end points are known and relate to each other with the attenuation coefficient in a frequency range. The relation between the seismic amplitudes at z distance from each other can be expressed as a linear function of frequency after a few modifications. SRM uses the linearity of the logarithmic ratio of the seismic amplitudes over a frequency range. In theory, ratios plotted against a frequency range must produce a flat line. However, in practice, the logarithmic ratios are expected to draw an approximate line (curve), where some of the data points deviate from the origin of the line. Thus fitting a line to the ratios curve and calculating the slope of this curve are necessary. Slope of the curve relates to the seismic attenuation coefficient and further to the seismic Q. The SRM results suggest that Bentonite may have a Q value as low as 5. This highly attenuative and thin (20 to 40 feet throughout the south central Cut Bank Unit) layer alters seismic signals propagating through it. A thorough analysis of the amplitude spectra suggests that seismic signals dramatically lose their energy when they pass through Bentonite. Low energy content of the signals below the Bentonite layer highlights that the recovery of the seismic energy is less likely despite the presence of multiples, which are known to affect the seismic signals constructively. Therefore, separation of reflected events is a greater challenge for the thin reservoir sand units lying underneath the Bentonite layer. Thus the Bentonite layer in the Cut Bank oil field has to be taken seriously and data processing should be done accordingly for better accuracy.