Two marine walkaway VSP lines are recorded by three-component receivers positioned in a dolomite layer. The layer has a high seismic velocity relative to the surrounding rocks and may be fractured. The recorded wavefield is analysed to determine whether this acquisition is suitable to image details of the internal structure of the layer. The principal arrivals in the wavefield are a dominant ho...

[1] Modulation of whistler mode chorus waves, which plays an important role in driving the pulsating aurora and other processes related to energetic electron dynamics, is an interesting but a long‐standing unresolved problem. Here we utilize in situ observations from the THEMIS spacecraft to investigate the role of density variations in the modulation of the chorus wave amplitude, which forms a...

We study the onset and development of an ultra low frequency (ULF) pulsation excited by a storm sudden commencement. On 30 August 2001, 14:10 UT, the Cluster spacecraft are located in the dayside magnetosphere and observe the excitation of a ULF pulsation by a threefold enhancement in the solar wind dynamic pressure. Two different harmonics are observed by Cluster, one at 6.8 mHz and another at...

A RECENT seismic refraction profile1 in 2,800 fm. (5.1 km.) at latitude 34° 00' N, longitude 66° 30' W, in the Atlantic Ocean proved that basement rocks having a velocity of 7.58 km/sec. for compressional waves were covered by 1.37 km. of sediment. We tentatively identified this velocity with either the P n velocities used in earthquake seismology for the ultra basic layer immediately beneath t...

Response of a fabric to applied forces normal to its plane is known as fabric compressional behavior. It is one of the important properties that determine fabric performance in many applications. The principle of a system used to measure fabric compressional characteristics, online, is proposed in this paper. A controllable nip formed by a pair of rollers is employed to apply compressional defo...

Low-frequency acoustic-energy sources for waveform logging have important applications in: 1) Verifying theoretical calculations; 2) generating tube waves in large-diameter boreholes; and 3) providing larger sample volumes in cases where borehole effects are important. A new low-frequency source was fabricated by modifying an existing acoustic-waveform logging system to discharge multiple capac...

The traveltime of compressional (P) and shear (S) waves have proven essential in many applications earthquake exploration seismology. An accurate efficient computation for P S is crucial the success these applications. However, solutions to Eikonal equation with a complex phase velocity field anisotropic media challenging. first-order, hyperbolic, nonlinear partial differential (PDE) that repre...

A perturbation model for high-frequency sound scattering from an irregular elastic sea bed is considered. The sea bed is assumed homogeneous on the average and two kinds of irregularities are assumed to cause scattering: roughness of the water-sea bed interface and volume inhomogeneities of the sediment mass density and the speeds of compressional and shear waves. The first-order small perturba...