ZURICH (Reuters) - The nuclear proliferation watchdog CTBTO said unusual seismic activity detected in North Korea on Saturday took place around 50 km (31 miles) from previous tests.  Korean Peninsula unusual #seismic activity: LAT=41.36 LON=129.76 mb=3.5 About 50 km from prior tests. #CTBT Analysts investigating,  CTBTO Executive Secretary Lassina Zerbo said in a Twitter post. 
Korean seismic activity took place 50 km from prior tests: CTBTO