SEATTLE (NEWS 1130) – It has now been a week since the Great BC ShakeOut and there is up to a 14 per cent chance of a major earthquake hitting the Cascadia subduction zone in the next 50 years, which includes Vancouver, according to the U.S. Geological Survey.
But some new research out of the U.S. focusing on simulations, has come up with some surprising results.
“One of the things that we saw in our simulations — and we ran a number of simulations because we wanted to see the full range of possibilities — is that we do see the effects of rupture directivity,” explains geophysicist Dr. Erin Wirth, who conducted much of the research while at the University of Washington and is now with the U.S. Geological Survey.
It all depends on a number of factors like how deep the hypocentre is and the type of soil where it hits, but that rupture directivity has to do with the centre of a quake’s proximity to a centre.
“If the earthquake is rupturing towards you, seismic energy can pile up and result in stronger shaking,” says Wirth.
“(Conversely) if the earthquake is rupturing away from you, such as can happen if the hypocentre is say right near you, all of that energy is directed at other places. So the shaking can be less,” she adds.
That suggests that should a magnitude-9 earthquake hit, it may actually be better for it to happen closer to the centre of a city.
The simulations focused on Seattle but did extend north.
“Our model does extend up to southern British Columbia and includes Vancouver. Our focus has been on Seattle thus far but these simulations will be made available over the next few months and people can use them to study the impact of a magnitude 9 earthquake in Vancouver,” says Wirth.
They also looked at Portland and Victoria, all of which sit on major fault lines.
The next step is to study how tall buildings in those cities would react given their proximity to such a quake.