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A laboratory perspective on accelerating preparatory processes before earthquakes and implications for foreshock
Thomas H W Goebel1, Valerian Schuster2, Grzegorz Kwiatek2
1University of Memphis, Center for Earthquake Research and Information, Memphis, TN, USA. thgoebel@memphis.edu.
Nature Communications
|July 3, 2024
Summary
Foreshock activity duration is shortened by high fluid pressures and low fault heterogeneity. This leads to faster slip acceleration and fewer, more earthquake-like acoustic emissions, especially on immature faults.
Area of Science:
- Geophysics
- Earthquake Science
- Seismology
Background:
- Dynamic failure in laboratory settings is often preceded by foreshocks accompanying premonitory aseismic slip.
- Aseismic slip is hypothesized to govern earthquake nucleation in nature, yet natural foreshocks are infrequent.
Purpose of the Study:
- To investigate the influence of fault heterogeneity (roughness, damage, pore pressure) on premonitory slip and acoustic emission characteristics.
- To understand why foreshocks are rare in natural earthquakes despite the role of aseismic slip.
Main Methods:
- Laboratory experiments simulating fault behavior under varying conditions of roughness, damage, and pore pressure.
- Analysis of premonitory slip acceleration and acoustic emission (AE) patterns.
- Characterization of AE focal mechanisms.
Main Results:
- High fluid pressures increase fault stiffness and reduce heterogeneity, promoting rapid slip acceleration and shorter precursory periods.
- Low geometric heterogeneity (smooth faults) similarly accelerates slip and shortens precursory periods.
- Acoustic emission activity in low-heterogeneity samples shows an increasing dominance of earthquake-like double-couple focal mechanisms.
Conclusions:
- Increased stress and geometric homogeneity, akin to high fluid pressure and reduced roughness, can significantly shorten foreshock duration.
- Gradual fault activation and extended foreshock activity are more probable on immature faults at shallow depths.
