# Reverse slip direction

Dear everyone,

I would like to ask about the reverse slip direction to be used in the interseismic simulation. In the example 3d subduction step03.cfg, the reverse slip sign for the slabbot is (-). It indicates the fault of slabbot is subducting downward. This also makes sense according to figure 6.2. But why the sign for slabtop in creep spatial database is (+). Depth less than 60km is 0 means locking. But why the reverse slip is (+) but not (-).

Thank you in advance.

Best Regards,
Alvina K K

The slab is subducting so the sense of slip is the opposite on top of the slab as it is on the bottom. This is most easily seen in Step 2 of Figure 7.45 (2D subduction example).

I understand that.
But I used the reverse slip sign (-) for the slabbot and reverse slip (+) for the slabtop in my geometry and I obtained different results in my simulation. Where in the interseismic simulation, the displacement on top of the locked depth should be in positive values (as shown in the subduction example). But for my geometry, I had to change the reverse slip sign, slabbot is (+), slabtop is (-) in order to get a similar result as shown in the example. My geometry is the same in my previous question (Define up_dir value - #6 by alvinakkuncoro).
Could you please let me know how to solve this?

Thank you in advance.

Best Regards,
Alvina K K

If you needed to reverse the sense of slip signs on both the top and bottom of the slab it means PyLith reversed the fault normal direction while inserting the cohesive cells. We try to detect the fault normal direction and define the sense of slip so that it follow seismological conventions, but sometimes the sense of slip can end up reversed. Plotting the fault directions usually shows the reversal (normally the fault normal direction has an +z component) so you can confirm that this is the issue.