I am researching the effect of fault on a tunnel stability in depth of 60m. This tunnel is under seismic load with a PGA equal to 0.5g. I have corrected this record by SHAKE in depth of 60 m to apply this load at the base of model. I know that this converted load will amplify through passing the model but I don't know how to model this effect? It is obvious that the maximum acceleration of earthquake in depth is not so considerable, but it is amplified gradually. How can I model this property of earthquake in UDEC?