Evaluation of seismic site response of submarine clay canyons using centrifuge modelling

The morphological features of submarine canyons significantly modify the amplitude, duration and frequency content of free-field seismic ground motions. This paper examines the influence of these morphological features through a series of seismic centrifuge tests on kaolin clay models with canyon sloping angles of 15, 30 and 45 degrees. These tests were performed using the IFSTTAR (the French Institute of Science and Technology for Transport, Development and Networks) geotechnical centrifuge at an acceleration of 40g by applying a set of dynamic excitations, varying in amplitude and frequency content. The response of the clay canyon models was monitored by means of accelerometers and pore-pressure transducers. In-flight characterisation was performed on each clay model with bender element and T-bar tests prior to the application of seismic excitations. The study shows that the topographic shape of the canyon can substantially affect peak values and the frequency content of the free-field motions along the slope surface. Low-intensity seismic excitations and frequency contents along with the dominant frequency of the soil deposit were found to cause substantial amplification. In addition, the reduction of the shear modulus and the corresponding increase in damping tend to increase the fundamental site period.