Numerical modelling of seismic wave propagation through a soft-sediment filled basin near Kinburn, ON.

The unique geological conditions present around the Ottawa region provide the framework for strong amplifications of earthquake ground motions in areas with deep soil, and a basin structure of the bedrock surrounding the soil. Previous techniques used to identify the amplifications at a soil site compared to a rock site have been unable to account for the large amplifications recorded under these conditions. A soft-sediment filled basin was identified near Kinburn, Ontario and was instrumented with several seismometers to record the motions throughout the basin. The basin was explored through several geophysical methods to determine the impedance boundary between the soft sediments and bedrock. A model was created from these measurements in order to complete numerical simulations of the basin. Several 2D profiles were derived from this model along the short and long axes of the basin. Numerical modelling was performed on the model of the basin using a spectral element method and varying physical properties for the material within the basin and for the rock surrounding the basin. These simulations delineate the amplifications within the basin which were caused by the transfer of energy from rock to soil, and those which were caused due to the shape and structure of the basin. The numerical modelling was performed on both a 2D and 3D homogenous model of the region to recreate the ground motions recorded at a seismic recording station located close to the basin, but placed on a rock outcrop. The soft-sediment basin was added to the model and both the rock station and soil station at the centre of the basin were simulated for the 2013 Ladysmith earthquake. These motions show similar properties for the first arrivals to the recorded motions at the same location as a result of this earthquake. The simulations were also used to identify different wave types and arrival times within the basin along with the expected motions at other locations within the basin.