26. Earthquakes and Landscapes

Photo 47: A fault in the rock (left of the tree) at Maligne Canyon, Jasper National Park, Alberta. 2011-05-19

Earthquakes

Colliding lithospheric plates cause earthquakes. The seismic waves of these quakes travel throughout the lithosphere and upper mantle of the earth, causing dislocated strata, open fractures, scarps and lines of crushed rock. Earthquakes can also cause mudslides, Tsunamis, snow avalanches, and rock avalanches like in the former town of Frank, Alberta (photo 48).

Epicentre is a well-known term, but this actually represents the spot on the Earth’s surface right above the focus point (origin) of the earthquake, and is not itself the point of the earthquake. The magnitude of an earthquake is measured by a seismograph and based on the Richter scale. This is a logarithmic scale invented by the American seismologist Charles Richter in 1935.

Fault Line

Photo 47 displays a fault line, to the left of the tree. The fault line in this rock might have been caused by water expansion as it froze during the winter. A fault line is a key term in regards to earthquakes as well. It marks a breaking point of the crust, where the plates on both sides of the fault line don’t move together in the same direction. Rocks have certain plasticity and will deform slightly before breaking. At the breaking point, the rocks will snap back into their original form and cause an earthquake. The fault plane is the plane of contact between 2 planets. The fault scarp is the side of the higher plate, visible with vertical plate movement. The fault trace is the line of debris along the fault line on the lower one of the two plates.

Photo 48: The site of Frank slide, Alberta. On April 29, 1903, at 4:10 am, a wedge of limestone over 1 km wide, 425 m long
 and 150 m deep broke of the top of Turtle Mountain. In 90 seconds the town of Frank was covered with rocks, some
still quite large as the photo shows. Few inhabitants of the town survived. 2009-09-07