'Megaquake' explained: Japan issues warning after 7.1-magnitude earthquake

NBC News' Dana Griffin reports on the significance of Japan issuing its first-ever 'megaquake' warning. » Subscribe to NBC News: https://www.youtube.com/user/NBCNews NBC News Digital is a collection of innovative and powerful news brands that deliver compelling, diverse and engaging news stories. NBC News Digital features NBCNews.com, MSNBC.com, TODAY.com, Nightly News, Meet the Press, Dateline, and the existing apps and digital extensions of these respective properties. We deliver the best in breaking news, live video coverage, original journalism and segments from your favorite NBC News Shows. Connect with NBC News Online! Breaking News Alerts: https://link.nbcnews.com/join/5cj/breaking-news-signup?cid=sm_npd_nn_yt_bn-clip_190621 Visit NBCNews.Com: https://www.nbcnews.com/ Find NBC News on Facebook: https://www.facebook.com/NBCNews Follow NBC News on Twitter: https://twitter.com/NBCNews Get more of NBC News delivered to your inbox: nbcnews.com/newsletters #japan #earthquake #nbcnews