On the seismic source function of an underwater explosion

Summary The massive eruption of the Hunga Volcano on 15 January 2022 provides an ideal test case for reviewing established methods to discriminate and analyse source processes. Discriminating source mechanisms and identifying their origins is a key task when analysing suspicious events in the frame of the Comprehensive Nuclear-Test-Ban Treaty. Earthquakes and explosions can be distinguished in some cases using well established methods such as inversion for the seismic moment tensor. In more complex cases the combination of analyses of the seismic, infrasonic and hydroacoustic waveform content can be of help. More challenging is the discrimination of the specific kind of explosive source such as a nuclear test and a volcano eruption based on the data from the three waveform technologies alone. Here, we apply standard techniques destined to analyse relevant events in the frame of the CTBT, i. e. all three waveform technologies (seismology, infrasound, and hydroacoustic) and atmospheric transport modelling of radionuclides. We investigate the potential of standard analysis methods to discriminate a source and identify their possible weaknesses. We show that the methods applied here work very well to identify, investigate, and discriminate an explosive event. During discrimination we could not only exclude a shear-source (i. e. earthquake) but also distinguish the volcanic explosion in contrast to a man-made explosion. However, some tasks remain difficult with the available methods. These tasks include the reliable estimation of the strength of a non-shear event and thereupon a yield estimation of a possibly CTBT relevant event. In addition to evaluating our methods, we could relate our results with specific phases of the eruption process providing a more detailed insight of what happened. Our investigations of the eruption details only provide a starting point for further in-depth analysis. However, they underline the importance of the Hunga eruption event for science. The huge amount of observations provide a unique opportunity for knowledge gain in several sub-disciplines of the geosciences. In addition, although not being a nuclear test, it also provides a useful and important data set for further developing multi-technology analyses in the frame of the CTBT.

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Source Spectra of Pg and Lg Waves from North Korean Nuclear Tests Estimated Using a Nonmodel-Based Approach

Jin,

Xu,

Ding

et al. 2023

Bulletin of the Seismological Society of America

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In this article, we demonstrate that source spectra for regional seismic waves generated by an underground explosion may be uniquely extracted using a simple linear regression method between the geometrical spreading corrected displacement spectra and epicentral distances as long as the recording stations are well distributed in distances. Using this method, source spectra of Pg and Lg waves from North Korean nuclear tests conducted between 2009 and 2017 are estimated, respectively, and are compared to test the conjecture of Fisk (2006) as well as to determine the relative size between the seismic moment of Lg waves and that of compressional waves. For a specified explosion, the resultant Pg and Lg source spectra approximately have equal low-frequency source level. Based on this result, it is estimated that for the explosions seismic moment of Lg waves would be about 35% of that of compressional waves. In addition, it is shown the Fisk conjecture approximately stands, as for a specified explosion the observed Pg and Lg source spectra share the same manner of high-frequency rolloff as f−2, the source corner frequency of Lg waves is smaller than that of Pg waves by a factor of about 1/3, and the Pg source spectrum exhibits a prominent overshoot, whereas it is not obvious in corresponding Lg source spectrum. The new method for source spectra estimation may have a promising application prospect in monitoring studies. As an example, it is shown that the yield and even buried depths of the North Korean nuclear explosions may be reasonably estimated by fitting the observed Pg source spectra using an MM71- (Mueller and Murphy, 1971) and DJ91 (Denny and Johnson, 1991)-based hybrid source model suggested by Ford and Walter (2013).

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On the seismic source function of an underwater explosion

Cited by 4 publications

References 30 publications

Signal characteristics and energy transmittance during detonation tube excitation in a gas–water–soil environment

Signal characteristics and energy transmittance during detonation tube excitation in a gas–water–soil environment

The January 2022 Hunga Volcano explosive eruption from the multitechnological perspective of CTBT monitoring

Source Spectra of Pg and Lg Waves from North Korean Nuclear Tests Estimated Using a Nonmodel-Based Approach

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