Earthquake magnitudes, efficiency of stations, and perceptibility of local earthquakes in the Lake Mead area

摘要: Summary . About a quarter of the local earthquakes recorded at Boulder City are from focal distances five miles or less, and approximately another between ten miles. As these so close to Lake Mead stations, they studied in somewhat different fashion those which far away that depth becomes negligible. It has been possible with new formula make an extrapolation Gutenberg-Richter Magnitude Scale down one mile distance. With this extended scale magnitudes more than 1,000 collected into frequency distribution tables polygons for years 1941–1942. These show increase efficiency locating power seismograph system better coverage decrease distance stations when fourth station is added. They instrumental magnification. The mode magnitude most frequently located shocks dropped 3.0 early 1941 2.5 were cut probable epicenters by added Dam. 2.0 last half 1942 after Benioff seismographs placed operation three other stations. More total energy released annually largest shock group maximum magnitude. equal 1941. perceptibility range small appears be linear function distances. Under exceptional circumstances, very felt, apparently following equation Δ = 6 M − 2 where generally, there chance earthquake will felt reported if equation used: 8 11 This holds less destructive To extend large derived: log 0.5 + 0.25 1 / This shallow focus.