  Abstract Compared to existing schemes, the decomposition of moment tensors
for mining-induced seismic events into closing-crack and double-couple
components has the advantage that each can be interpreted in terms of a
physical source process (excavation convergence and slip/shear, respectively).
Obviously, not every moment tensor permits such a decomposition, and we
translate existing bounds on those that do to the Hudson source-type plot. For
moment tensors falling within these bounds, it has previously been noted that
there will be a infinite set of possible decompositions in general. We derive
an implicit equation defining this set and suggest physically motivated
criteria that can be used to select a single decomposition from it.
Furthermore, for moment tensors falling outside the source-type bounds, we
present a simple geometric scheme for determining the closest moment tensor
within them (which can then be decomposed). To demonstrate the methods
developed in this paper, we apply them to two catalogues of mining-induced
seismicity.
