Prognosis of pool phase state and hydrocarbon fluid composition for the Pre-Caspian OGP

The results of detailed studies and interpretations are presented for composition variations, structural properties and the phase state of hydrocarbon fluids from subsalt pools of the Pre-Caspian depression. These data serve as a basis for substantiating the existence of several types of condensate, and identifying the locations of the main centres of fluid generation. The basic geological-geochemical conditions controlling the composition of condensate and free gases have been determined as well as their present phase state. A set of basic criteria is proposed as well as prognostic maps for the condensate and free gas composition, and the pool phase states.     

Effect of tilt on strong motion data processing

In the near-field of an earthquake the effects of the rotational components of ground motion may not be negligible compared to the effects of translational motions. Analyses of the equations of motion of horizontal and vertical pendulums show that horizontal sensors are sensitive not only to translational motion but also to tilts. Ignoring this tilt sensitivity may produce unreliable results, especially in calculations of permanent displacements and long-period calculations. In contrast to horizontal sensors, vertical sensors do not have these limitations, since they are less sensitive to tilts. In general, only six-component systems measuring rotations and accelerations, or three-component systems similar to systems used in inertial navigation assuring purely translational motion of accelerometers can be used to calculate residual displacements.     

Low-velocity zone and topography as a source of site amplification effect on Tarzana hill,California

Tarzana station is located in the foothills of the Santa Monica Mountains in California near the crest of a low (<20 m) natural hill with gentle slopes. The hill is about 500 m in length by 130 m in width and is formed of extremely weathered shale at the surface to fresh at depth. Average S-wave is about 250 m/s in the top 17–18 m, and S- and P-wave velocities significantly increase below this depth. According to the NEHRP classification based on V_S30∼300 m/s it is a site class D. Strong-motion instrumentation at Tarzana consisted of an accelerograph at the top of the hill, a downhole instrument at 60 m depth, and an accelerograph at the base of the hill. More than 20 earthquakes were recorded by at least three instruments at Tarzana from 1998 till 2003. Comparisons of recordings and Fourier spectra indicate strong directional resonance in a direction perpendicular to the strike of the hill. The dominant peaks in ground motion amplification on the top of the hill relative to the base are at frequencies ∼3.6 and 8–9 Hz for the horizontal components. Our hypothesis is that the hill acts like a wave trap. This results in an amplification at predominant frequencies f=V/4 h (h is layer's thickness) at f∼3.6 Hz for S-waves (using average V_S17=246 m/s and h=17 m) and f∼7.9 Hz for P-waves (using average V_P17=535 m/s and h=17 m). As was shown by Bouchon and Barker [Seismic response of a hill: the example of Tarzana, California. Bull Seism Soc Am 1996;86(1A):66–72], topography of this hill amplifies and polarizes ground motion in the frequency range of 3–5 Hz. Hill acts as a magnifying polarizing glass: It polarizes ground motion in the direction perpendicular to the strike of the hill and also amplifies ground motions that had been also amplified by a low-velocity layer.     

Response of pendulums to complex input ground motion

Dynamic response of most seismological instruments and many engineering structures to ground shaking can be represented via response of a pendulum (single-degree-of-freedom oscillator). In most studies, pendulum response is simplified by considering the input from uni-axial translational motion alone. Complete ground motion however, includes not only translational components but also rotations (tilt and torsion). In this paper, complete equations of motion for three following types of pendulum are described: (i) conventional (mass-on-rod), (ii) mass-on-spring type, and (iii) inverted (astatic), then their response sensitivities to each component of complex ground motion are examined. The results of this study show that a horizontal pendulum similar to an accelerometer used in strong motion measurements is practically sensitive to translational motion and tilt only, while inverted pendulum commonly utilized to idealize multi-degree-of-freedom systems is sensitive not only to translational components, but also to angular accelerations and tilt. For better understanding of the inverted pendulum's dynamic behavior under complex ground excitation, relative contribution of each component of motion on response variants is carefully isolated. The systematically applied loading protocols indicate that vertical component of motion may create time-dependent variations on pendulum's oscillation period; yet most dramatic impact on response is produced by the tilting (rocking) component.