Researchers have recently conducted a study on the Mw 6.0 mainshock and Mw 4.5 aftershock using cross-correlation methods. The study, which focused on understanding the characteristics and behavior of these seismic events, yielded significant findings.
Using the Empirical Green Functions (EGFs) at a frequency band of 1โ5 Hz, the researchers cross-correlated the mainshock waveform with the aftershock. Notably, correlation peaks were observed across all channels in both the P and S-phase correlograms. However, in the P correlogram, the correlation peaks after the first peak were not as prominent. This could be attributed to the radiation pattern and the proximity of the DAS array to the P nodal line.
Interestingly, the study found that the coda waves were more prominent and contributed more to the individual P correlogram. In addition, the S-phase correlograms of the Mw 4.5 aftershock exhibited a simpler rupture process compared to the mainshock.
Further analysis was conducted by increasing the frequency band to 1โ8 Hz and stacking the correlograms using the same EGF. This approach revealed another correlation peak before the highest correlation peak. Moreover, the use of another EGF enhanced this additional correlation peak.
To compare the results, the researchers examined the normalized vertical-component recordings of both EGF events on a nearby broadband station. Surprisingly, similarities were observed at different frequency bands, indicating significant seismic activity.
In order to visualize the back-projection volume and reduce ambiguity, the researchers employed back-projection imaging using both P and S phases. Notably, the P and S beam power exhibited different slopes due to differences in slowness. By using joint P and S back-projection, the distance-time trade-off was reduced, enabling a clearer interpretation of subevents. To further minimize swimming artifacts and enhance interpretation, a “slowness time slice” technique was adopted.
Overall, this study provides valuable insights into the characteristics and behavior of the Mw 6.0 mainshock and Mw 4.5 aftershock. By employing cross-correlation methods and observing the correlation peaks across different channels and phases, researchers have advanced our understanding of these seismic events.
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