ABSTRACT

Spectral ratio discriminants were developed to discriminate between low‐magnitude (MN<2) shallow (depth <3  km) earthquakes and blasts related to road construction. The spectral ratios were formed from narrowband spectral‐energy estimates between 1 and 40 Hz of Pg, Lg, and Rg for a total of 786 unique discriminants. From these discriminants, it was found that broadband high‐frequency Pg/Lg and low‐frequency Lg/Rg provided the largest separation between earthquakes and blasts. The high‐frequency Pg/Lg spectral ratio confirms the applicability of P/S ratios for the discrimination of low‐magnitude blasts from small local/regional shallow earthquakes. Furthermore, the success of the Lg/Rg spectral ratio demonstrates that the normalized Rg component from blasts typical of road construction projects tends to be larger at small epicentral distances (<50  km) than that of shallow earthquakes typical of the area. Although the results presented in this work were developed for a local area, the broader conclusions are likely expandable to other regions in Canada, in particular the Northern Appalachians, where discriminating between low‐magnitude blasts related to mining and road construction and shallow earthquakes is a daily challenge.

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