What caused the massive earthquake in Nepal?
Nepal is positioned in the middle of a slow-motion collision between the India and Eurasia tectonic plates. The force of that convergence started to form the Himalayan mountain range 50 million years ago -- and it continues to this day.
Above is a map showing all the earthquakes in the region since 1994 that have a magnitude of at least 4.0. The data was taken from
You can compare that to North America鈥檚 West Coast, where you can see the past year of seismic activity. There are fewer earthquakes -- although that doesn鈥檛 mean there鈥檚 less danger.
鈥淭hat relative infrequency of seismicity belies the fact that we do get very large earthquakes -- of course, the magnitude 9 that people refer to -- every 550 years on average,鈥� said Michael Bostock, a professor in seismology at the University of British Columbia.
Unlike the Himalayas, earthquakes along the West Coast are caused by three tectonic plates -- the massive Pacific and North America plates, and the smaller Juan de Fuca plate.
In Canada, running north from the top of Vancouver Island to Haida Gwaii, the Pacific plate is shifting northwest past North America.
Below that, and to the west, the smaller Juan de Fuca plate is sliding underneath the North America plate -- a process called subduction -- that is forcing Vancouver Island upwards and to the northeast.
The Juan de Fuca plate is converging with the North America plate at a rate of four centimetres per year. 鈥淭hat鈥檚 roughly the rate at which your fingernails grow,鈥� Bostock said.
He also noted it鈥檚 the same rate of convergence that鈥檚 happening in the Nepal region between the India and Eurasia plates.
But most of the earthquakes on Canada鈥檚 West Coast are not directly caused by the subduction process in that convergence.
鈥淭here are a range of fault systems off the West Coast and the majority of the earthquakes actually are associated not with the subduction zone per se, but more to do with the spreading ridge -- the Juan de Fuca spreading ridge and the Queen Charlotte fault,鈥� said Bostock.
Further south of Vancouver Island, the Pacific plate creates more pressure against the North America plate, creating huge regions of seismic activity like the famous San Andreas fault line, which runs through California.
