Discrimination of earthquakes and explosions in southern Russia using regional high-frequency three-component data from the IRIS/JSP Caucasus network

Abstract

High-frequency regional records from small earthquakes (magnitude <4.5) and comparable magnitude chemical explosions are analyzed to find a reliable seismic discriminant in southern Russia near Kislovodsk. The digital, three-component seismograms recorded during 1992 by the Caucasus Network operated by Lamont-Doherty Earth Observatory since 1991 in the distance ranges 15 to 233 km are used. Mean vertical-component Pg/Lg spectral amplitude ratios in the band 8 to 18 Hz are about 1.3 and 3.2 for earthquakes and explosions, respectively, in this region. We find that the vertical-component Pg/Lg spectral ratio in the frequency band 8 to 18 Hz serves quite well for classifying these events. A linear discriminant function analysis indicates that the Pg/Lg spectral ratio method provides discrimination power with a total misclassification probability of about 7%. The Pg/Lg spectral ratios of rotated, three-component regional records improve the discrimination power of the spectral ratio method over the vertical-component Pg/Lg ratios. Preliminary analysis indicates that distance-corrected vertical-component Pg/Lg ratios improve the discrimination power by about 4% over uncorrected ratios. But we find that an even better discriminant is the Pg/Lg spectral ratio of the three-component regional records corrected for the free-surface effect. In the frequency band 8 to 18 Hz, the free-surface-corrected three-component Pg/Lg spectral ratio provides discrimination power with a total misclassification probability of only 2.6%. Free-surface-corrected and network-averaged Pg/Lg spectral ratios provide transportability of the spectral ratio method to various regions worldwide.

P/SVAmplitude Ratios of Shallow Isotropic Explosions and Earthquakes Could Be Indistinguishable at Local Distances: Insights from Single-Station Waveform Simulations

“…The vertical-component P/S amplitude ratio has been successfully and widely adopted for seismic discrimination between explosions and earthquakes in the past decades (e.g., Kim et al, 1993;Zhao et al, 2008;Wang et al, 2020), though average values on three components result in more stable results (e.g., Kim et al, 1997). Our results suggest that such success of P/S discrimination is likely attributed to source depth difference (i.e., earthquakes have larger source depths than explosions) rather than the source mechanism itself (i.e., doublecouple source vs. explosive source), similar to the Lg/P discrimination (Baker et al, 2004).…”

“…For example, the difference between body-and surface-wave magnitudes (i.e., M s : m b ; e.g., Selby et al, 2012), the difference between local and coda duration magnitudes (i.e., M L − M C ; e.g., Koper et al, 2008Koper et al, , 2021, the amplitude ratio (e.g., Taylor et al, 1989;Walter et al, 1995) or spectral ratio (e.g., Fisk, 2006) of compressional and shear waves (e.g., Pg/Sg, Pn/Sn, Pg/Lg, Pn/Lg). However, the discrimination criteria of the aforementioned methods may be subjective in different studies, though the discrimination performance can be improved using network-averaged results (e.g., Pyle and Walter, 2019;Wang et al, 2020) and distance corrections (e.g., Kim et al, 1997), especially for the low-yield event discrimination at local distances (e.g., <50 km in O' Rourke et al, 2016;<150 km in Koper, 2020;Koper et al, 2021;<200 km in Pyle and Walter, 2022). The classification discrepancy is highlighted by the debate on the seismological evidence for the existence of a low-yield nuclear test by North Korea in May 2010 (Schaff et al, 2012;Ford and Walter, 2015;Zhang and Wen, 2015;Kim et al, 2017).…”

Achievements and Prospects of Global Broadband Seismographic Networks After 30 Years of Continuous Geophysical Observations

“…Though often based on data only from the vertical component of recorded ground motions, W.-Y. Kim et al (1997), showed that the ratio can more effectively discriminate when the amplitudes of P-and S-motions are based on all three components of ground motion. The discriminant is effective also for small events-a point that has emerged from detailed studies of small earthquakes and explosions, for example, one using GSN data from station WMQ (Urumqi, Xinjiang Province, China) and MAKZ (Makanchi, Kazakhstan) (Pan et al, 2007).…”

Discrimination of Icequakes and Earthquakes in Southeast Alaska using Random Forest and Principal Component Analysis

“…In view of this, both the statistical and machine learning based methods have been developed and applied; these methods usually involve deriving a set of features from the event waveforms as a first step and then applying different classification techniques to these features. Statistical approaches include discriminating the events based on the ratio of amplitudes of different seismic phases (Rodgers & Walter, 2002;Taylor, 1996;Kim, 1997;Walter et al, 2018) , high and low frequency spectral amplitudes (Walter, 1995;Wang et al, 2021) , misfits of P-wave spectra to standard earthquake source model (Allmann et al, 2008) , and different kind of magnitudes (Holt et al, 2019;Koper et al, 2016;Wang et al, 2021) . While statistical approaches have shown a great promise for the events at teleseismic distances and the events with moderate to high magnitudes, their efficiency plunges at local to regional distances and for events of small magnitude (O'Rourke et al, 2016;Pyle & Walter, 2019) .…”