摘要
1 SURVEY OF GLOBAL SEISMICITY A total of 5 strong earthquakes with M S≥7.0 occurred in the first half of 2018(from January 1 to May 31,2018)throughout the world,according to CENC(China Earthquake Networks Center),including one with M S≥8.0(M W7.9),which occurred on January 23,2018 in Alaska(Fig.1).The 2018 M S8.0 Alaska earthquake was located in the north of the Circum-Pacific Seismic Belt.The mainshock was slip type and the rupture was unilateral along the NW direction,with maximum intensityⅩ.Features of global seismicity of M S≥7.0 in the first half year of 2018 are as follows.1.1 The Global Seismicity Was Similar to 2017 But Weaker Than Previous Years One earthquake with M S≥8.0 occurred in the first half of 2018.The global seismic strength stayed nearly the same compared with the earthquake with M S≥8.0 in 2017(Fig.2(a)).There were 5 earthquakes with M≥7.0 occurring in the world in the first half of 2018.The seismic frequency was similar to 2017,which had 8 strong earthquakes with M S≥7.0,but was significantly lower than the annual average of 19 strong earthquakes(Fig.2(b)).
