Damage amplification during repetitive seismic waves in mechanically loaded rocks.

Area of Science:

• Geophysics
• Rock Mechanics
• Materials Science

Background:

• Tectonically active planets experience inherent stress cycles.
• Stress oscillations and creep deformation cause strain and damage in rocks.
• Understanding material failure under cyclic loading is crucial for hazard assessment.

Purpose of the Study:

• To investigate damage accumulation and weakening in volcanic rocks under simulated seismic stress oscillations and creep.
• To quantify the impact of varying stress magnitudes and oscillation frequencies on rock mechanical response.
• To elucidate the role of microcracking in inelastic strain and material weakening.

Main Methods:

• Uniaxial compression tests on porphyritic andesites.
• Application of time-dependent creep loads (60-70% of failure stress).
• Superposition of repeating stress oscillations (±2.5-7.5% of creep load) at ~1.3 Hz.
• Microstructural analysis to examine fracture patterns and density.

Main Results:

• Stress oscillations induced greater damage and weakening compared to constant creep loads.
• Progressive microcracking was identified as the primary mechanism for inelastic strain.
• Higher stress oscillation amplitudes and pre-existing damage accelerated micro-crack coalescence and failure.
• Damage accumulation was quantified per oscillation event, showing initial rapid strain increase.

Conclusions:

• Repetitive seismic stress oscillations significantly amplify material damage and weakening.
• This process can alter geological structures, potentially affecting fluid pathways and future rupture vulnerability.
• Findings are relevant for understanding hazards in volcanic regions and assessing engineered structures.