Suqian ship lock group locates in the mid-south segment of famous Tancheng-Lujiang Fault

where a large earthquake of M8. 5 once occurred in history. From the view of interaction among fault

site and construction

the fault activity and seismic stability in the site of Suqian ship lock group are studied for the risk analysis and evaluation of site fault activity.The geological survey of the site shows that the main site fault across Suqian ship lock group affects the soil layers to a depth of 20 m or more which is 5 ?5 m under the base of lock chambers. The fault will not be exposed when the soil is excavated for building lock

whereas the distribution of faults provides a favourable tectonic condition for earthquake occurence. When the buried depth of fault exceeds a critical value

the surface dislocation caused by earthquake can be neglected. The survey data shows that the top of main fault of the site is 15 m below the base of lock chambers

therefore the possibility of surface dislocation and its influence on ship locks are relatively little.In the further analysis and evaluation of the risk of site fault activity effects

the elaspse rate and activity （in terms of average rate and seismic period） of fault and the seismic fragility of geological factors are taken into account. The formula for evaluating the risk of site fault activity effects is given as follows:HD = E×M/8 × [（x1+…+xn）/n]where HD is hazard degree of site fault activity effects

E is elapse rate of fault （ranging from 0 to 1）

M is the activity of fault represented in earthquake magnitude （M≥8）

.r

is the seismic fragility of geological factor represented in index of earthquake hazard （ranging from 0 to 1）

and n is the number of considered geological factors. HD ranges from 0 to 1

the larger the value of which is

the higher the risk of fault activity will be.Although the geological background of ship lock group and the global environment of the site are not favourable

it is found after the analysis of the mode of interaction among fault

site structure and ship lock group that the upper site soil layers connected the most closely with the ship lock have not been affected by main fault

which will ensure the ship lock running in safety. It is found after the synthetical analysis of the large amount of borehole data that there are stable silty clay and clay layers at the depth of 5. 5 m to 8. 5 m. It is suggested that the foundation of ship locks should lay on such layers

in order to obtain higher degree of safety.