Bug/unexpected behavior in parsing SRF files with zero slip faults

[dmelgarm]

We have some custom made SRF files that we are running through SW4, the runs terminated with no errors or warnings but the waveforms were defective. They contained only a few samples of zeros or very small numbers followed by many NaNs.

After comparison with the SRF files from /examples/ruptures we concluded the issue was with the zero slip subfaults. In the SW4 examples zero slip faults have a subfault header but nothing more. Meanwhile in our custom SRFs zero slip subfaults had subfault header and then a bunch of zeros representing zero slip rate for some length of time.

SW4 parses these file and reports no errors. I imagine at some point this makes a zero moment moment tensor and is the source of the issue.

After changing our custom SRF files to have only subfault headers in the zero slip subfaults the problem goes away.