All earthquakes in South Korea. Data: [1]
In 2016, South Korea was suffered from the strongest earthquake in history. [3], [1] South Korea is traditionally a country with low seismic activity. Such earthquakes are extremely rare for Korea. Even before this earthquake, experts stated that Korea is no longer safe from earthquakes. [4]
“I felt the ground vibrating while I was sitting in a restaurant. The building was shaky as if we were inside a makeshift building,”
—said Kim Hyung-zip, a 39-year-old office worker in Seoul, who was visiting Ulsan at the time. [4]
M>3 Earthquakes in South Korea. Data: [1], [2]
But it's not over. In 2017, Korea again encountered an large earthquake. It's the second-strongest earthquake in South Korea since the country officially began monitoring them in 1978. [5]
Debris from a collapsed wall is scattered in front of a shop after an earthquake in Pohang Min Kyung-suck/Newsis/AP. Image source: [5]
Quite strange. We can unambiguously conclude that seismic activity in Korea is now higher than ever for the entire time of observations.
References:
[1] https://web.kma.go.kr/eng/weather/kma_service/introduction.jsp
[2] http://www.naturalearthdata.com
[3] Park Si-soo, Chung Hyun-chae, Kim Rahn (2016, September 12). Strongest-ever earthquake hits Korea, tremors felt nationwide. Retrieved March 13, 2018, from http://www.koreatimes.co.kr/www/news/nation/2016/09/116_214014.html
[4] H. (2016, July 06). Korea no longer safe from earthquakes: experts. Retrieved March 13, 2018, from http://www.koreaherald.com/view.php?ud=20160706000745
[5] Agencies, S. A. (2017, November 16). South Korea earthquake: Tremors that rocked Pohang were second-strongest on record. Retrieved March 13, 2018, from http://www.independent.co.uk/news/world/asia/south-korea-earthquake-latest-pohang-quake-second-strongest-record-5-4-magnitude-a8057946.html