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The excitation of specimens in multiple modes enhances the characterization of granular materials. The purpose of this paper is to present the equipment modification and test procedure and data reduction for flexural excitation in a standard torsional-resonant column device. Typical results for dry and wet sand specimens are also presented. A salient advantage of the modified device is that it permits testing shear stiffness (torsional excitation) and longitudinal stiffness (flexural excitation) at frequencies which are relevant to high-resolution seismics and near-surface studies (approx. 50-200 Hz). High attenuation in flexural mode is measured in saturated and partially saturated specimens; local flow is suspected as a prevailing loss mechanism. Velocity and damping ratios are complementary indicators of saturation conditions prevailing in the specimen.Key words: mechanical waves, resonant column, velocity, attenuation, sands, modal testing.

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Deep-seated mud volcanoes are observed in a variety of geological settings, which has led to considerable debate on their origin. This paper summarizes the geological features common to mud volcanoes around the world and possible mechanisms of their extrusion. Field and laboratory data from Trinidad and Taiwan are discussed to assess the possible sources and causes of the volcanoes. A close association between mud volcanoes and compressional tectonics leads to the conclusion that tectonic activity plays an important part in mud volcano development. Experimental data are presented to explain the role of tectonic activity and the association between shear stresses and mud volcanoes. It is demonstrated that shear stresses applied to low permeability sediments can produce a dramatic increase in pore pressure and can cause sediment flow. This is proposed as one possible contributing cause of mud volcanoes.