Seismologist says tidal surge of up to one metre has been recorded in North Canterbury region of the New Zealand's South Island * USGS says quake magnitude revised to 7.8* Authorities issue tsunami alert, say waves could be 5 metres* Thousands flee homes to seek higher ground* Reports emerging of injuries, so far no reports of deaths* In 2011, a 6.3 quake killed 185 people in Christchurch (Adds authorities warning first tsunami waves may not be biggest)By Charlotte GreenfieldWELLINGTON, Nov 14 (Reuters) - A 7.8 magnitude earthquake struck central New Zealand just after midnight, the U.S. Geological Survey said, causing...