Reading a report from a seismometer is similar to reading a book, said Ian Saginor, Ph.D., an assistant professor of earth science at Keystone College. The red and black lines are created as time passes - at the end of each hour, a new line is created. Time is indicated in Greenwich Mean Time, which is Eastern Standard Time minus 4 hours.
On Tuesday, two earthquakes show up in the reading. The first, in Colorado, registered locally just before 10 a.m. GMT/6 a.m. EST, shown in black in the upper right and continuing in red at the upper left. The second quake, in Virginia, struck about 17:51 p.m. GMT/1:51 p.m. EST, indicated on the graph in black starting in the lower right and continuing in red in the lower left.
Source: Keystone College