The Relevance of Foreshocks in Earthquake Triggering: A Statistical Study

Area of Science:

• Geophysics
• Seismology
• Earthquake Science

Background:

• Increased seismic activity, known as foreshocks, often precedes major earthquakes.
• The Epidemic Type Aftershock Sequence (ETAS) model explains many foreshock statistical features.
• However, the ETAS model does not fully account for observed foreshock patterns in instrumental seismic catalogs.

Purpose of the Study:

• To investigate common features of foreshocks across four different geographic regions.
• To identify limitations of the standard ETAS model in reproducing observed foreshock phenomena.
• To propose a generalized model that explicitly incorporates foreshock occurrence.

Main Methods:

• Statistical analysis of instrumental seismic catalogs from four distinct geographic regions.
• Comparison of observed foreshock frequencies with predictions from the standard ETAS model.
• Development and validation of a generalized ETAS model (ETAFS) to include foreshock dynamics.

Main Results:

• Instrumental seismic catalogs exhibit a significantly higher number of foreshocks than predicted by the standard ETAS model.
• This foreshock excess cannot be explained by catalog incompleteness.
• The proposed ETAFS model demonstrates strong agreement with observed statistical features of both foreshocks and aftershocks.

Conclusions:

• The standard ETAS model requires modification to accurately represent foreshock behavior.
• The generalized ETAFS model provides a more comprehensive framework for understanding earthquake sequences.
• The ETAFS model shows improved agreement with instrumental data, enhancing the reliability of earthquake precursory pattern analysis.