Scientists will be studying this week’s devastating tornadoes in the same way that detectives investigate a crime scene: They plan to interview witnesses and watch surveillance video, among other methods, in an effort to determine how many tornadoes touched down and how powerful they were. Researchers have to be on the scene quickly to preserve as much evidence as possible. They expect to learn a lot from the destruction patterns: A mobile home, for example, would be destroyed by winds of 110 to 135 mph, but better constructed buildings would only have been destroyed by much stronger tornadoes. The National Weather Service already determined that one of the tornadoes would be given the worst possible rating of EF-5, and it expects that many more will be designated in the same way. So far, none of the tornadoes have been rated less than EF-3, which means there were winds of 140 to 150 mph. The final report will become part of the National Climate Database, a record of the nation’s most severe weather. A similar investigation of a series of disastrous tornadoes that struck in 1974 took 15 years to complete.