New Study Analyzes Correlation Peaks in Earthquake Aftershocks
A recent study conducted by researchers has delved deeper into understanding the correlation peaks in earthquake aftershocks. The study specifically analyzed the correlograms of the Mw 6.0 mainshock and its aftershock, focusing on the frequency band of 1-5 Hz.
The findings of the study revealed several noticeable correlation peaks in the a, b, P, and S-phase correlograms, all marked by arrows. However, in the P correlogram, peaks after the first one were found to be less distinguishable. This could possibly be attributed to the radiation pattern and the proximity of the DAS array to the P nodal line. Interestingly, the coda waves were found to be more prominent and contributed significantly to the individual P correlogram.
Further analysis of an Mw 4.5 aftershock, with a depth and focal mechanism similar to the mainshock, showed only one horizontally aligned correlation peak in the S-phase correlograms. This suggests a simpler rupture process in this specific case.
Increasing the frequency band to 1-8 Hz and stacking the correlograms using the same EGF (Envelope Gain Function) brought forth another correlation peak before the highest peak. The correlation peak was enhanced even more when another EGF was used. These findings were further supported by the normalized vertical-component recordings of both EGF events on a nearby broadband station, which exhibited similarities at different frequency bands.
To carry out this study, the researchers employed a back-projection imaging technique that utilized both P and S phases. The P and S beam power exhibited different slopes due to differences in slowness, which helped to reduce the distance-time trade-off. Instead of using conventional constant-time slices, the study utilized a “slowness time slice” methodology, which effectively decreased swimming artifacts and ambiguity in interpreting subevents.
To effectively visualize the back-projection imaging process, the study provided a schematic diagram. The diagram portrayed blue and red contours representing the P and S beam power, respectively.
This study adds valuable insights into the understanding of correlation peaks in earthquake aftershocks and highlights the importance of considering frequency bands and using appropriate techniques for accurate analysis. Further research in this field can potentially lead to improved earthquake prediction and management strategies.