According to Biot's (1956a, b) model, the presence of water plays an important role in the propagation of seismic waves in at least three different ways: (1) in an infinite medium, water saturation induces an attenuation that can be accounted for by a complex formulation of wave velocities, as in viscoelastic media; (2) at the boundaries of the saturated medium, pore pressure and water flux determine specific continuity conditions; and (3) there is a second compressional wave, called the P2 wave. In this paper, we discuss the latter two effects. Biot's model is presented first, with homogenization theory used to provide the numerical values of the different coefficients used in the model. In an infinite medium, the model is of practical interest when the frequency ƒ is about the same order of magnitude as a characteristic frequency noted ƒc, which depends on the properties of the constituents. This limits the application of Biot's model to a few particular fields in geophysics. In a layered medium, Biot's model has a wider scope in that it provides a tool for modeling fluid-solid interaction at the boundaries of the saturated medium. This is illustrated in our paper for the case of a very permeable water-saturated surface layer over an elastic half-space. Two examples are given; in the first example (rigid sands) we discuss the physics of the strongly attenuated P2 wave predicted by Biot, the amplitude of which becomes significant when the ƒ/ƒc ratio is about equal to or greater than 0.1. In the second example (soft unconsolidated sediments) the P2 wave is negligible, but the calculation of the complete wave field is required when the ƒ/ƒc ratio is about 0.01. There is no adequate equivalent single phase model that gives a correct estimation of the amplitude of the ground motion. In this case, we argue that the P2 wave is not important in itself, but Biot's model allows the description of the fluid-solid interaction at the water table; continuity of effective stress and pore pressure can be explicitly formulated.

Seismic wave propagation in a very permeable water‐saturated surface layer

Eight records of seismic-induced pore-water pressure and corresponding acceleration records were gathered from aftershocks of the 25 to 27 May 1980, Mammoth Lakes, California, earthquake sequence. The records were obtained from lakeshore sediments at Convict Lake that had undergone liquefaction and subsequent lateral-spreading failure. The pore-pressure records showed several similarities to corresponding strong-motion acceleration records. The pore-pressure traces show clear P - and S -wave phases and are in phase with corresponding P -wave components of the acceleration records. S -wave components of pore-pressure records appear most similar in waveform to one or the other of the corresponding horizontal acceleration components. Although the P -wave portions of pore pressure are in phase with their acceleration counterparts, the amplitudes are not related by a strictly proportional factor. S -wave portions of the porepressure records show a phase lag compared to the S wave of the respective acceleration trace. In most cases, the frequency of the pore-pressure S -wave components are also about 5 Hz lower in frequency than the acceleration S waves.

Seismic-induced pore-water pressure records from the Mammoth Lakes, California, earthquake sequence of 25 to 27 May 1980

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Analysis of Rigid Retaining Walls During Earthquakes

Seismic Response of Pore Water Pressure in Surface Sand Layer

Although described as a Guide, the 1984 design manual for foundation design forms part of the enforcement system of the Earthquake Resistance code in Japan. The Guide applies knowledge gained from recent unexpected experiences, notably the damage to prestressed high‐strength concrete (PHC) piles in the Off‐Miyagi earthquake without any effects from change in ground conditions, such as liquefaction. This review is by the Head of the Geotechnical Engineering Division of the Japanese Building Research Institute, who chaired the Working Party on the Guide.

Masatake Naganou

Papers

Record of Lateral Pressure Taken During Earthquake