Normal fault earthquakes or graviquakes

Area of Science:

• * Seismology and Tectonophysics: Investigating earthquake generation mechanisms in extensional tectonic settings.

Background:

• * Traditionally, earthquakes are understood as the release of elastic energy accumulated during interseismic periods.
• * In extensional settings, gravity acts as a primary energy source for hangingwall fault collapse, a concept distinct from elastic rebound.

Purpose of the Study:

• * To differentiate the energy accumulation and dissipation mechanisms of normal faults (graviquakes) from strike-slip and contractional settings.
• * To explore the relationship between fault geometry, volume, and seismic energy release in extensional tectonics.

Main Methods:

• * Analysis of gravitational potential energy as the primary driver for normal fault earthquakes.
• * Comparison of fault mechanics and energy budgets between extensional (normal faults) and other tectonic regimes (strike-slip, contractional).
• * Examination of fault dip angles, involved volumes, and their correlation with seismic energy release and earthquake magnitude.

Main Results:

• * Gravitational potential energy is significantly larger (approx. 100x) than observed earthquake magnitudes in extensional settings.
• * Normal faults exhibit unique energy dynamics ('graviquakes') where gravity drives motion, unlike elastic-driven faults.
• * Larger fault volumes and steeper dips correlate with increased vertical displacement and seismic energy release; however, maximum graviquake volumes are smaller than in other settings, leading to higher b-values and lower maximum magnitudes.
• * Low-friction rocks can lead to fault creep, dissipating gravitational energy without significant seismic release.

Conclusions:

• * Normal faults in extensional settings operate via a distinct 'graviquake' mechanism, primarily driven by gravity.
• * The phenomenology of graviquakes differs from other earthquake types, influencing their magnitude, b-value, and precursor characteristics.
• * Understanding graviquakes is crucial for accurately modeling seismic hazard in extensional tectonic environments.