Inversion techniques for focal mechanism determination of small-magnitude earthquakes: a comparative study using the Burewala earthquake (\(M_w\) \(\sim \) 4) in Pakistan

Abstract

The focal mechanisms of small-magnitude earthquakes can be challenging due to sparse networks, limited availability of velocity models, and a lack of suitable approaches. In this study, three techniques were used to determine the focal mechanism of the Burewala earthquake (\(M_w\) \(\sim \) 4) in Pakistan, which occurred on March 18, 2022. Full waveform inversion yielded different results for the local and regional velocity models. Although the regional velocity models showed a better waveform fit, the thrust mechanism solutions obtained did not match first-motion polarities. Therefore, cyclic scanning of polarity solutions was employed to combine polarities and waveforms, but the solutions were unreliable due to poor station coverage. Therefore, the inversion of waveform envelope technique was used, which is less sensitive to velocity models; hence, it can be used for sparse networks. The mechanism (i.e., normal faulting with a minor strike-slip component) was obtained for local and regional velocity models. The obtained solutions were consistent with the waveform inversion results based on the local velocity model. Thus, envelope inversion is deemed a more suitable technique for analyzing small-magnitude earthquakes.