 This is a seismic hazard map of the continental US, produced by the US Geological Survey. There's two types of data that go into making a map like this. And one is knowledge of where earthquakes happen. The second is knowledge of how far away you can feel shaking from any given earthquake. How far away you can feel shaking is a function of both the size of the earthquake and also some characteristics of the rocks in that area of the country. Now the colors denote the level of horizontal shaking that is calculated to have a 1 in 50 chance of being exceeded in a 50 year period. And the colors are all percentages of little g, where little g is 9.8 meters per second squared. So for the next three weeks, we will explore why the new Madrid seismic zone, which is right here, has a color that is just as high as the west coast of the United States over here. So this is far away from a plate boundary. Why is the seismic hazard so high there?