Are you at risk from a major earthquake and/or tsunami?
Earthquakes
Earthquakes occur as a result of plate tectonics, where one plate slides under another, as happens in Cascadia (click on the picture to enlarge). The picture shows the Cascadia subduction zone which runs from northern California to Vancouver Island in Canada, and is associated with the Cascade Range of volcanoes.
 Photo courtesy of USGS.
Most subduction zones around the Pacific Rim or in South East Asia, like the one that caused the December 26 2004 tsunami.
There are also earthquakes associated with volcanoes and other events. Most earthquakes, however, occur where there are faults, or breaks, in the Earth's crust, where the rocks on each side are moving in different directions. The greater the friction between the two, so that they lock together, then the larger the quake when the stress finally gives way. The may lead to further stress at a nearby fault, which may also give way, and so on. This can give rise to a series of earthquakes in a rough line over a period of says, weeks, years or decades or more.
When an earthquake occurs, the compression waves travel fastest. If there were a major earthquake in the Cascadia subduction zone, for example, these would reach Seattle in a couple of minutes, and cause the ground to rise. Shortly afterwards there would be shear waves moving the earth from side to side by up to a metre and surface waves, making the ground ripple like ocean waves. Skyscrapers would wobble like jelly. This would last about 5 minutes. Un-reinforced masonry buildings could collapse. For those on the Pacific NorthWest coast, there could still be the tsunami to come, with no time for a warning (the earthquake would have to serve as warning). The tsunami would be caused by vertical movement of the Earth underwater, displacing the water. The wave could last several minutes. It would reach other parts of the world, such as Japan, later, so that warning could be given. In Japan it would be known as an orphan tsunami, as it would not be accompanied by an earthquake there.
Recent news stories involving earthquakes include:
Plate find may force Tokyo to rethink quake plans
Another tectonic plate has been discovered under the Tokyo area, making the forecasting of, and preparations for, future earthquakes more complex. Current estimates are that a major earthquake has a 90% chance of occurring in the area in the next 50 years.
Please see the following message for the remaining stories. Sue [sysop in NewsForum, World Issues, All Animals forums] | 
