Page - 458 - in Book of Full Papers - Symposium Hydro Engineering

Table 1 Details of the seismic catalogue Year Frequency Frequency in different magnitude Maximum magnitude ML<1 1<=ML<2 2<=ML<3 3<=ML<4 4<=ML 2002 24 0 0 20 4 0 3.9 2003 3 0 3 0 0 0 1.9 2004 0 0 0 0 0 0 / 2005 13 0 10 3 0 0 2.2 2006 1003 321 415 212 42 13 4.6 2007 27 25 2 0 0 0 1.6 2008 20 18 2 0 0 0 1.3 2009 21 19 1 1 0 0 2.8 2010 72 53 18 1 0 0 2.1 2011 46 34 12 0 0 0 1.8 2012 14 14 0 0 0 0 0.9 2013 6 5 1 0 0 0 1.1 2014 4221 3103 889 178 43 8 4.4 2015 334 239 76 18 1 0 3.4 2016 104 73 25 5 1 0 3.9 Total 5908 3904 1454 438 91 21 / Fig. 2 Daily variations of seismic frequency (bottom bar) in 2014 Blue curve: water level 2.2. SEISMIC MAGNITUDE Fig. 3 shows that the relationship between water level and seismic magnitude. Combining Table.1, Fig.1 and Fig.3, we recognize that the seismic cluster ② and ④ are much bigger that the other two clusters not only in magnitude but also in frequency. And the seismic activities are mainly weak or micro earthquakes. Actually, more than 99% of the seismic events are smaller than ML4.0. In addition, the biggest seismic event is ML4.6 (Feb 9th, 2006), which is right after the water level decreasing dramatically from the first reach of 145+m. 458