The geomorphological nature of the seafloor, with different slope angles, canyons and associated drainage features plays an important role in the seismic response of the continental margins around the globe. These characteristics influence the amplitude and frequency content of the seismic waves and therefore become important factors influencing seismic hazard evaluations. Even in low seismicity regions, seismic resistant design is necessary to ensure safe development of offshore activities. This study examines the influence of morphological features through a series of seismic centrifuge tests on kaolin clay models with canyon sloping angles of 15, 30 and 45° , therefore of increasing depth. The canyon models analyzed here are similar to the submarine geomorphology of the deep-water area of south-eastern Brazil. These tests were performed using the IFSTTAR geotechnical centrifuge at an acceleration of 40g by applying a set of dynamic excitations, varying in amplitude and frequency content. The responses of the clay canyon models were monitored using accelerometers and pore pressure transducers. In-flight characterization of the clay models were performed using a T-bar penetration and Bender Element (BE) devices prior to the application of the seismic excitations. The study shows that the low intensity seismic excitations and frequency contents along with the dominant frequency of the soil deposit were found to cause substantial amplification. In addition, topographic amplification factors were found to be more significant than soil amplification factors due to the nonlinear soil behavior. The study aims to improve the understanding of topographic amplification in order to mitigate the seismic risks to submarine structures.
Samuel F. M. Tarazona, Maria C. F. Almeida, Márcio S. S. Almeida, Sandra Escoffier and Lucas C. Takayassu
Keywords: centrifuge study, canyons, seismic response
Publisher: DFI