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Feedback between megathrust earthquake cycle and plate convergence.
Juan Martin de Blas1, Giampiero Iaffaldano2,3, Andrés Tassara4
1Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark. jmb@ign.ku.dk.
Scientific Reports
|October 31, 2023
Summary
Plate motion slows before major Andean earthquakes. This study reveals that tectonic plate convergence rates decrease in the decade leading up to large megathrust events, challenging previous assumptions.
Area of Science:
- Geophysics
- Tectonics
- Seismology
Background:
- Andean orogeny results from Nazca and South America plate convergence over millions of years.
- The megathrust earthquake cycle operates on decadal/centennial timescales.
- Plate convergence rates are assumed constant during the earthquake cycle, despite long-term feedback.
Purpose of the Study:
- To investigate if Nazca/South America plate motion varies over year/decade periods.
- To determine if megathrust stress variations influence plate motion during the earthquake cycle.
Main Methods:
- Analysis of geodetic data for Nazca and South America plate motion.
- Focus on the decade preceding major Andean megathrust earthquakes (2010, 2014, 2015).
- Comparison of observed plate motion slowdowns with torque variations from interseismic stress buildup.
Main Results:
- Observed slowdowns in both Nazca and South America whole-plate motions.
- Slowdowns exceed data uncertainty and noise.
- Required torque variations for slowdowns are consistent with interseismic stress accumulation.
Conclusions:
- Contemporary Nazca/South America plate motion is not steady during the megathrust earthquake cycle.
- Interseismic stress buildup preceding major earthquakes causes measurable variations in plate convergence rates.
- A short-term feedback mechanism between megathrust stress and plate motion is identified.
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