No Signal (image) The Earth Institute at Columbia University Share Print E-Mail Caption This shows 24 hours of data from a seismic station in Mudanjiang, China, on the date of one purported 2010 North Korean nuclear test. Background levels are higher during working hours than at night, suggesting human causes such as traffic, electric motors and passing trains -- but there is no indication of a nuclear explosion, say the authors of a new paper. Each line represents one hour, sampled 40 times per second. Credit Courtesy Schaff et al., 2012 Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.