• Matched-filter function
• EQcorrscan
• Earthquake event detection and analysis
• Template matching analysis

Genoa City is the capital of Genoa province with slightly over half a million residents, a total area of 93 square miles (240 square km), and occupies a narrow coastal plain and the western slopes of the Apennine Range. The city’s maximum altitude reaches 496m and has several small drainage basins. Its geology is mainly characterized by heterogeneous Flysch belonging to the Antola and Ronco Tectonic Units and by Pliocene clay deposits. The city was hit by a moderate magnitude 4.0 earthquake 10.5 km from the city in the early afternoon of Thursday, September 22, 2022, at 13.39 local Italian time. Due to the quake’s shallow depth of 8 km, shaking intensity was from level V-I moving away from the epicenter and created light to moderate shaking and slight indoor damages predominantly dishes. Usually, such earthquakes are followed by smaller ones known as aftershocks. the Genoa earthquake was followed by 6 (six) aftershocks within magnitudes 2.3 and 2.7 and within a 3 Km radius of the mainshock. More aftershocks of even smaller or larger magnitudes might have hit but were not detected by the city’s seismic stations. Detecting these aftershocks requires the application of earthquake event detection algorithms such as EQcorrscan template matching (matched-filter function). This function applies the cross-correlation technique to calculate the cross-correlation coefficient between continuous and template waveforms and detect an event when this coefficient exceeds a set threshold.

The primary objective was to apply a template-matching technique to detect and analyze the quake’s undetected aftershock events using the EQcorrscan template-matching algorithm. The study was limited to 8 days of recorded seismic data from two seismic stations along three channels and 7 template events reported in the INGV catalog. Template waveforms were extracted from continuous data processed at 100Hz and bandpass filtered within 1-10 Hz. The matched filter function was implemented using an optimum threshold of 50. The function detected 35 seismic events of which 7 were duplicates while 28 were new with unique origin times. 68.4% of the unique events’ traces were clean while 31.6% were noisy traces. 49.56% of the unique events’ traces had amplitude values of equal to or greater than 4e3 while 50.43% had amplitude values <4e3. Clean and noise-free unique events’ traces were predominantly from station RNCA while noisy traces were predominantly from station GENL. The explanation is associated with the stations’ location. RNCA is in the outcast of Genoa making it free of disturbances from human activities while GENL is just in the city, and this creates lots of noise and disturbances due to human activities.