Create undulating strata inside the model

Hi guys, I have created a surface in vol 1 and I want to divide vol 1 into upper and lower volumes using that surface as a dividing surface, how do I do that or can I do anything about it, I hope you can give me some advice, appreciate it. Here is a prototype of what I did.`reset
brick x 100 y 80 z 50
move vol 1 x 50 y 40 z -25

create vertex 0 0 -25
create vertex 0 80 -25

create vertex 20 0 -20
create vertex 40 0 -30
create vertex 60 0 -20
create vertex 80 0 -30
create vertex 100 0 -25

create vertex 20 80 -20
create vertex 40 80 -30
create vertex 60 80 -20
create vertex 80 80 -30
create vertex 100 80 -25

create curve spline vertex 9 10
create curve spline vertex 9 11 12 13 14 15
create curve spline vertex 10 16 17 18 19 20
create curve spline vertex 15 20

create surface curve 13 14 16 15`
image

Hi,
you can use a webcut to split the volume.

webcut volume 1 with sheet extended from surface 7

Thanks for your help! it helps me a lot.