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Investigation of Full Moment Tensor Solutions for Earthquakes and Announced Nuclear Tests at the Punggye-Ri Test Site, DPRK

Description: 

Event Screening is the rejection of the hypothesis that a seismoacoustic event is generated by a single explosion source. There are several methods used to screen events, including the ratio of body-wave to surface-wave amplitudes, the ratio of high frequency P-wave to S-wave energy, and source depth. However, these methods may not screen all relevant events and so forensic seismologists have looked for additional approaches. The full moment tensor solution (MTS) resolves the six independent components of the source moment tensor, and therefore fully characterises the source mechanism, including determining the proportion of deviatoric and isotropic energy released by a source. However, complications arise from sources at shallow depths where the moment tensor inversion becomes underdetermined. Furthermore, explosions can generate deviatoric energy, complicating the MTS.

Here, we use the mttime inversion scheme (e.g., Chiang et al., 2021), utilising data from IRIS, the International Data Centre (IDC) and recently published additional datasets, to calculate MTSs for: six announced DPRK nuclear tests, the collapse event after DPRK6, and nearby earthquakes in the IDC Reviewed Event Bulletin (REB). After tuning of station-specific time-shifts and velocity models, all six announced nuclear explosions have large positive isotropic components, with significant deviatoric components in their final MTSs, whereas the collapse event has a large negative isotropic component. In contrast, the earthquake MTSs have larger deviatoric components in comparison to isotropic. However, in all cases the compensated linear vector dipole component (volume expansion along a plane) is substantial, and solutions are not always stable; small adjustments in the time shifts, velocity model and station distribution can produce highly variable seismic source interpretations. Thus, care must be taken in determining the cause of a seismic source.

UK Ministry of Defence © Crown owned copyright 2024/AWE

Session: Advancements in Forensic Seismology and Explosion Monitoring [Poster Session]

Type: Poster

Date: 5/2/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Christopher

Student Presenter: No

Invited Presentation: 

Authors