In this report, results of earthquake observation of improved ground by Deep Mixing Method, which has been carried out at Daikoku in Yokohama Port, was analized. The improved ground whose base ground is still soft clay from -49m to -73m is called floating type.
　The results of observation are summerized as follows:
(1) When the accerelation of improved ground indicates maximum value, vibration mode of original soft ground was the second or the third mode.
(2) Dynamic behavior of the floating type improved ground was the same as that of original ground in low frequency range but in high frequency range behavior of the improved ground was different from that of original ground.
(3) The vertical maximum accerelation of improved ground was almost the same as that of horizontal one. However maximum accerelation of either horizontal and vertical motion did not appear at the same time.
(4) The horizontal translation motion at the gravity center of improved ground was dominant in horizontal accerelation of improved ground. However the rotational motion was not negligible in vertical accrelation of improved ground.
(5) FEM analysis using equivalent linear method can explain results of observation.