Abstract Whether seismicity is correlated with the solid Earth tides has been a longstanding problem, but the findings remain ambiguous. The attempts at its resolution shed light on the physical properties and processes controlling earthquake triggering. The recent surge in earthquake data and advancement in detection techniques provide an opportunity to revisit this problem. We utilize a 40‐year Southern California Seismic Network catalog and a 10‐year Quake Template Matching catalog to explore the tidal modulation in Southern California. Results indicate that the correlations between earthquakes and tides vary with location. Regions where seismicity is significantly modulated by tidal stresses have relatively low effective background normal stress (20–155 kPa), which are primarily associated with geothermal locations. Additionally, deeper earthquakes in certain areas have a stronger correlation with tides. These phenomena suggest that faults with lower effective background stress might be more sensitive to tidal modulation. Furthermore, earthquakes of specific types (strike‐slip and thrust) in certain areas are more likely to correlate with tides, suggesting that different fault types experience different tidal loading amplitudes. Our study suggests that earthquake catalogs covering longer time spans with smaller completeness magnitude are required for more robust tidal modulation analysis, and the modulation of seismicity by tides provides a probe to measure the effective background normal stress on the faults at depth.
Lu et al. (Mon,) studied this question.