The fault planes provided by the NSHM are approximations for the actual fault interface, simplified to allow for easier simulation.
In most cases the differences between the approximation and the actual interface are insignificant, however for faults with large curvature this may introduce a large error.
As the Hikurangi subduction fault is the largest fault we simulate, the fault has been extensively investigated and the subduction interface has a lot of curvature, this makes it a prime candidate for fitting the NSHM plane to a curved surface.
NHM faults
In the NHM the Hikurangi subduction fault is broken down into three sections, each with two sizes:
HikHBay (In the area of Hawkes Bay), HikRauk (In the area of Raukawa), HikWgtn (In the Wellington Region)
Each has the suffix of min and max, representing the smallest and largest ruptures expected. The min fault planes are subsets of the max fault planes, and so are not investigated to begin with.
Curved surface
For this investigation and application we will use the interface model from Charles Williams et al.
The original model comes from a 2013 paper, with a further update provided by Williams.
To increase the accuracy of the fault geometry the dip and depth of the fault should be changed to match that of the surface.
The dip was calculated by taking the leftmost and rightmost depths (Ignoring duplicate points such as those visible at the top of HikRaukmin) and calculating the dip angle.
The depth difference was calculated by taking the difference in depth at the center point.
Fault | Dip | Depth | |
---|---|---|---|
Hbay | min | 4.65 | 0.33 |
max | 5.65 | 1.47 | |
Rauk | min | 9.29 | 2.47 |
max | 11.44 | 1.97 | |
Wgtn | min | 10.0 | 2.22 |
max | 10.3 | 1.75 |
After applying these values the following changes were achieved:
The surface is in orange, while the srfs are in blue.
The bug resulting in Wgtnmax being translated/rotated but not curved has not yet been found.
Performance improvements have been made to allow for more rapid testing/debugging