Tsunami simulations

by Tyler Shendruk

Published: 10/20/10

The problem
IN THE YEAR 1700, a megathrust earthquake (that’s science talk for scary-big-earthquake) occurred along the Cascadia fault in the Pacific Ocean. The fault runs along the coast from Vancouver Island down to northern California. The earthquake triggered a tsunami off the Pacific Coast, which resulted in a flood that reached inland as far as the mouth of the Fraser River, travelling all the way across the Pacific Ocean and striking the coast of Japan.

The researcher
Engineering professor Ioan Nistor is fascinated by such tsunamis. After the 2004 Southeast Asia earthquake, he and his collaborators were the first research team in the tsunami-affected areas of Thailand and Indonesia. While in the field, they inspect damage to buildings and structures. Back in his University of Ottawa lab, Nistor measures the force of surge impacts on models. He then compares what he saw in the field to laboratory and numerical models in order to gain a better understanding of the effects of tsunami bores—the fast moving walls of water that occur once tsunamis break near shore.

The project
Nistor ruminates over the various scenarios that could result from a modern-day earthquake along the Cascadia fault. By simulating earthquakes at various points along the fault and the propagation of the waves towards shore, he is able to predict the resulting tsunami’s height and speed as it crashes inland. Nistor uses these values to estimate the strength of disastrous forces to which coastal buildings would be subject.

The key
Even though the major Canadian cities on the West Coast are located on inland waterways, simulations show that they would not be spared from devastation in the event of another Cascadia tsunami. Even though its approach is slowed in shallow waters, Nistor still expects 25-metre high surges.
Current building codes in Canada do not explicitly provide special design guidelines for structures located on tsunami-vulnerable shores. They do not account for the initial surge forces, the sweeping drag force, the increase in hydrostatic pressure, or the buoyancy force as the building floats away from its foundation. By properly quantifying these extreme loads on structures during inundation, new design guidelines for structures in tsunami-prone zones can be recommended and, in the event of a disaster, save countless lives.