- Most earthquake damage is caused by ground shaking. The magnitude or size (energy release) of an earthquake, distance to the earthquake focus or source, focal depth, type of faulting, and type of sub-surface material are important factors in determining the amount of ground shaking that might be produced at a particular site.
- Where there is an extensive history of earthquake activity, these parameters can often be estimated. In general, large earthquakes produce ground motions with large amplitudes and long durations. Large earthquakes also produce strong shaking over much larger areas than smaller earthquakes do. In addition, the amplitude of ground motion decreases with increasing distance from the focus of an earthquake.
- The frequency content of the shaking also changes with distance. Close to the epicenter, both high- (rapid) and low (slow)-frequency motions are present. Farther away, low-frequency motions are dominant, a natural consequence of wave attenuation in rock. The frequency of ground motion is an important factor in determining the severity of damage to structures and which structures are affected.
- The earth does not open up during an earthquake. A common misconception is that of a hole in the ground that opens during an earthquake to swallow up unfortunate victims. This has nothing to do with reality but is Hollywood's version of earthquakes. After a strong earthquake, some cracks may be seen on the ground or in basements. These are not faults, nor are they crevasses ready to close up again. These cracks are most likely due to soil settlement caused by the ground shaking.
- After a strongly felt earthquake, it is quite possible that people may feel shocks for up to several months after the initial shock. This possibility always exists, but keep in mind these four facts:
- In most cases, these shocks (called aftershocks) will be smaller; therefore, the vibrations will be weaker.
- Aftershocks do not mean that a stronger earthquake is coming.
- Aftershocks are normal; they show that the earth's crust is readjusting after the main earthquake.
- The number of felt aftershocks is quite variable and thus cannot be predicted. There might be several per day, or only several per week.
- Currently seismologists are not able to predict either the number or the magnitude of aftershocks that might occur. These vary greatly from one region to another, according to many factors which are poorly understood.
B.C. Earthquake and Tsunami Exercise
Exercise Coastal Response is Western Canada’s first, full-scale earthquake and tsunami response is a test of the B.C. Immediate Response Plan (IRP) that outlines the steps that the Province and its partners will undertake in the immediate aftermath of a massive earthquake. The goal is to exercise elements of the IRP and strengthen relationships among and across partners and stakeholders to enhance operational co-ordination. Learn more about Exercise Coastal Response