A new paradigm for large earthquakes in stable continental plate interiors

Présentation d'Eric Calais (ENS) au 1er Workshop Résif "Aléa sismique" | 27 et 28 septembre 2016, Strasbourg

Transcript

1. E. Calais (Ecole normale supérieure, PSL Research University, CNRS, Paris, France), T. Camelbeeck (Royal Observatory, Brussels, Belgium), S. Stein, Department of Earth and Planetary Sciences, Northwestern University, USA, M. Liu (Department of Geological Sciences, University of Missouri, USA), T.J. Craig (Institute of Geophysics and Tectonics, University of Leeds, UK)
2. “Earthquakes occur as a result of global plate motion” (Kanamori and Brodsky, Rep. Prog. Phys., 2004) Earthquakes result from the localized accrual of tectonic stress at long- lived active faults in a steady-sate system where a balance is achieved between the rates at which strain accrues and is released on faults. SCR faults = very, very, very, very slow faults.
3. There is no evidence for present- day, localized strain accumulation in SCRs In the NMSZ, seismic strain release is ~one order of magnitude larger than strain accumulation over past 3,000 yrs  Not steady-state  Releases “fossil” strain GPS (upper bound) Strain accumulation rate
4. There is long wavelength horizontal deformation in GIA areas, which does not correlate with current seismicity => strain accumulation and release should be thought of as decoupled GPS raw GPS filtered strain rates seismicity
5. SCR seismicity appears clustered and migrating through time 2000 years of migrating earthquakes in North China Liu et al., Lithosphere, 2011 Steady-state earthquake activity does not persist in the long-term on any single SCR fault. The Hebron fault, Namibia 50 km-long rupture Late Pleistocene to recent no current seismicity White et al., 2009
6. SCR faults are at failure equilibrium in a pre-stressed crust able to sustain large differential stresses. −103˚ −103˚ −102˚ −102˚ −101˚ −101˚ −100˚ −100˚ −99˚ −99˚ −98˚ −98˚ −97˚ −97˚ −96˚ −96˚ −95˚ −95˚ −94˚ −94˚ 33˚ 33˚ 34˚ 34˚ 35˚ 35˚ 36˚ 36˚ 37˚ 37˚ 38˚ 38˚ 1973-1990 −103˚ −103˚ −102˚ −102˚ −101˚ −101˚ −100˚ −100˚ −99˚ −99˚ −98˚ −98˚ −97˚ −97˚ −96˚ −96˚ −95˚ −95˚ −94˚ −94˚ 33˚ 33˚ 34˚ 34˚ 35˚ 35˚ 36˚ 36˚ 37˚ 37˚ 38˚ 38˚ 1991-2005 −103˚ −103˚ −102˚ −102˚ −101˚ −101˚ −100˚ −100˚ −99˚ −99˚ −98˚ −98˚ −97˚ −97˚ −96˚ −96˚ −95˚ −95˚ −94˚ −94˚ 33˚ 33˚ 34˚ 34˚ 35˚ 35˚ 36˚ 36˚ 37˚ 37˚ 38˚ 38˚ 2006-2015 Red line = Meers fault
7. Parvie scarp [3-10 m], ~10 ka, 155 km long SCR lithosphere stores elastic energy over time scales that are longer than observable by geodesy or paleoseismology
8. SCR earthquakes are better explained by transient perturbations of local stress or fault strength that release elastic energy from a pre- stressed lithosphere rather that by the localized accrual of tectonic stress at long-lived active faults. in SCR settings, stress accrues at very slow rates and earthquakes occur as a result of fault strength change (black line, e.g., fluid pore pressure increase at seismogenic depth) or of transient stress perturbations (blue line, e.g., hydrological or sedimentary load change).
9. • Corollaries: – SCR earthquakes can occur in regions with no previous seismicity and no surface evidence for strain accumulation. – They need not repeat, since the tectonic loading rate is close to zero. – Concepts of recurrence time or fault slip rate do not apply. • Some perspectives: – What data do other SCRs have to offer? Australia? – Is there evidence for a correlation between triggering mechanisms and earthquakes in SCRS? – How does SCR lithosphere stores strain? The Hebron fault, Namibia 50 km-long rupture, no current seismicity