# Question in modifying geometry for the slab detachment benchmark

Hello all,

My name is Hannah and I’m a student using ASPECT for a final project for my geodynamics course. I am not a modeler (I study isotope geochemistry in a clean lab), so please excuse my question for being rather simplistic. I’ve been modifying the slab detachment benchmark for a variety of geometries with varying degrees of success. I’ve been able to change the slab dip to 45 degrees for 2 different geometries, using the following modifications (apologies that I can’t attach more images, since I am a new user I am only allowed 1).

Modification 1: # Description of the initial compositional fields mantle and slab
subsection Initial composition model
set Model name = function
subsection Function
set Variable names = x,z
set Function expression = if((x<290000.0&z<330000.0)|(z<x+40000&x>=290000.0&x<540000.0)|(z<580000.0&x>=540000.0),0,1)
end
end

Modification 2: # Description of the initial compositional fields mantle and slab
subsection Initial composition model
set Model name = function
subsection Function
set Variable names = x,z
set Function expression = if((x<z-120000.0&z<580000.0)|(x<=210000.0&z<=x+120000.0)|(z<330000.0&x>=210000.0&x<290000.0)|(z<x+40000&x>=290000.0&x<540000.0)|(z<580000.0&x>=540000.0),0,1)
end
end

I am now trying to produce Modification 1 with a 30 degree angle. The geometry doesn’t work out as nicely as it did with a 45-45-90 triangle, so I am trying to characterize the equation of the line connecting points I’ve dubbed (x0,z0) and (x1,z1) but I’m getting wonky results (included below). Ideally the gap in the middle would be connected by a straight line. Does anyone have any tips, ideas, or can spot any oversights I’ve made? Let me know if I can provide any additional information to help. Thank you for your time.

Modification 3: # Description of the initial compositional fields mantle and slab
subsection Initial composition model
set Model name = function
subsection Function
set Variable names = x,z
set Function expression = if((x<107000.0&z<330000.0)|(z<5733.67*x+268221.7&x>=107000.0&x<540000.0)|(z<580000.0&x>=540000.0),0,1)
end
end

Modification 1:

Modification 2:

Hi Hannah,
Great to hear you’re using ASPECT for your geodynamics course. If I understand everything correctly, you need a line connecting the points (107,330) and (540,580) [km]. I’d therefore replace the bold part below with z<0.577367*(x-107000)+330000. Your current equation does not give the right z values for the considered x values. Hope that helps!
Anne

Thank you very much Anne!