Event Discrimination using Regional Moment Tensors with Teleseismic-P Constraints

Determining whether a seismic event is an earthquake, explosion, collapse, or something more complex can be done using regional (Delta < 13 degrees) intermediate-period (T > 10 s) full waveform moment tensors down to low magnitudes (M similar to 3.5). The moment tensor results can be improved for sparse station configurations when teleseismic (Delta > 30 degrees) array-based short-period (T < 1 s) P constraints are added. The inclusion of teleseismic-P aids in event discrimination because it samples the lower region of the focal-sphere, a region where intermediate-period waveforms recorded at the surface have low-sensitivity for shallow event depths. The teleseismic-P constraint is particularly useful in reducing the trade-off between a shallow explosion and a shallow volume-compensated linear-vector dipole with a vertical axis in compression. This trade-off can complicate discrimination. The teleseismic-P constraint is applied to the source-type analysis of the announced nuclear test of the Democratic People's Republic of Korea on 25 May 2009, resulting in greater confidence in a dominantly explosive solution.