MONITORING RESULT ANALYSIS OF SLOPE SEISMIC RESPONSE DURING THE KANGDING MS6.3 EARTHQUAKE

Many secondary natural geological disasters are caused by Lushan MS7.0 and Ludian MS6.3 earthquake. Some scholars consider the disasters may be associated with topographic amplification effect of seismic waves. But it is still lack of a large number of slope seismic response data to verify such hypothesis. The strong monitoring site of Luding Lengzhuguan is located on both sides of the Lengzhuguan valley, a tributary of the Dadu River and situated to the right back of the river. Tunnels excavated in different parts of the slope are used to place earthquake monitoring instruments on both sides of the valley. The instruments monitored the Kangding MS6.3 earthquake on November 22, 2014 in Sichuan, China. The earthquake monitoring data show the follows:(1)Reference to Kangding Guzan strong earthquake monitoring station of the main shock records(its horizontal and vertical PGA components are 16.4 and 15.7gal, respectively),the horizontal and vertical PGA amplification factors of the 1# monitoring site on the top of the peninsular terrain on the right bank reach 10.6-11.5 and 7.1,respectively. The Arias Intensity of the 1# monitoring site is largest. The Predominant Period was concentrated in the low-frequency, and horizontal to vertical spectral ratio reaches 11.1. The horizontal and vertical PGA amplification factors of the 2# monitoring site in the middle reach 4.3-5.0 and 2.3,respectively. Both of the Arias Intensity and horizontal to vertical spectral ratio were smaller than those at 1#.(2)The slope terrain variation on the left bank is small and the record of PGA is low.the result at the 5# monitoring site is enlarged obviously. The horizontal and vertical PGA amplification factors are 2.1-4.5 and 1.7-2.3,respectively. The monitoring sites on the left bank have several Predominant Period. The amplification effect is more prominent at high-frequency. The Arias Intensity of each is smaller than the right monitoring sites.(3)Ground motion topographic amplification effect in the nearly linear slope part is weak(6# and 7#).Some monitoring sites are narrowed to varying degrees. The amplification factor of the outside monitoring site is larger than the level depth of the inside monitoring site. Studies suggest that ground motion topographic amplification effect is obvious on both sides of the Lengzhuguan valley. The topography amplification effect of the peninsular terrain on the right bank is stronger than that on the left nearly linear slope. Furthermore, the amplification factor on the top of the peninsular terrain on the right bank is bigger than that on the middle. The topography amplification effect on the part of slope break is obvious and the part of nearly linear slope is weaker. According to direction of seismic wave propagation, the Lengzhuguan monitoring station is at the back side for Kangding earthquake. It is contrary for Lushan earthquake. Comparison of the results between the seismic data of Kangding earthquake and Lushan earthquake, it is found that the PGA amplification coefficients of each monitoring site during Kangding earthquake is bigger than those at Lushan earthquake. One result reaches to 5 times.