Jen,
Here is a reply from personnel at IGNS regarding the two faults you
mentioned.

"There are dozens of faults in the Cooke Strait. Two relatively active faults
have recently been mapped in detail by the National Institute for Water and
Atmospheric Research (NIWA) and these are the ones refered to. We often work
with NIWA when it comes to identifying active faults for our national hazard
models. These two faults are important because they may have generated M7+
quakes with a potential tsunami. They lie between Cooke Strait and run north
along the west coast of the North Island for a short distance (west of
Wellington)."