Event Discrimination using Regional Moment Tensors with Teleseismic-P Constraints

Abstract

Determining whether a seismic event is an earthquake, explosion, collapse, or something more complex can be done using regional (Δ 10 s) full waveform moment tensors down to low magnitudes ( M ∼3.5). The moment tensor results can be improved for sparse station configurations when teleseismic (Δ>30°) 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.