Last month, I read an interesting book, Disaster Deferred: How New Science Is Changing Our View of Earthquake Hazards in the Midwest, by Seth Stein. Stein is a Northwestern University geology professor who studies the New Madrid earthquake fault system. The New Madrid fault system, which is in southern Missouri, produced several large earthquakes in 1811-1812; these are sometimes described as the largest earthquakes on record in the contiguous United States, with magnitudes of 8 or more. However, Stein explains that their magnitudes were not this great (more like 7.2--7.4), and he details recent research in the fault system indicates that it is now quiescent. (GPS receiver networks placed on the fault system indicate very little movement; fault movement is what causes the strain that is released in earthquakes.) He concludes that recent assessments of the risk due to that fault are much too high, and that the resources being budgeted to mitigate that risk might be better spent on other hazards. I thought the book was credible, and it was interesting if only because I live this part of the country. But in fact, the book was well written; it gave clear, detailed and gentle explanations as to how earthquakes are studied and earthquake risks are assessed.
I might mention my own experience with earthquakes. This was here in Indiana. In April of 2008, I (and probably everyone in the Louisville area) was awakened at about 5:30 a.m. by a nervous sort of shaking, which lasted perhaps half a minute. This turned out to be due to a 5.3 magnitude quake that struck the Indiana-Illinois border west of Louisville. Later that afternoon, I felt an aftershock, which produced a gentle swaying motion. (I would have supposed that the building was swaying in the wind a little—but I was on campus in a concrete and steel structure.)