The best way to check if your modifications of TBB source code do not break anything is to run the TBB test suite. Call make test from the TBB folder to build the library and run all tests. You will need GNU make for that.
I am not sure whether the seismic simulation example has any built-in checks for result correctness; probably not.
To generate TBB_TRACE, re-compile the library with DO_TBB_TRACE defined to non-zero; put more TBB_TRACE calls in task.cpp if you need it. These calls are almost like printf, except that they need double parentheses. Since the TBB_TRACE macro expands to std::printf when DO_TBB_TRACE is defined to non-zero, the trace will be printed into stdout. It's a tool for internal debugging; we did not try to make it sophisticated.