Sujet de stage M2 / Master-level internship
Advisors: E. Calais [eric.calais@ens.fr], M. Ghil [michael.ghil@ens.fr], and Harsha Bhat [harsha.bat@ens.fr]
Internship location: Department of Geosciences, Ecole normale supérieure
Large earthquakes within stable continental regions (SCR) show that significant amounts of elastic strain can be released on geological structures far from plate boundary faults, where the vast majority of the Earth's seismic activity takes place [Calais and Stein, 2009]. SCR earthquakes show spatial and temporal patterns that differ from those at plate boundaries and occur in regions where tectonic loading rates are negligible [Calais et al., 2005, 2010]. Seismic activity in SCRs appears to be episodic and sometimes clustered on faults that are active during relatively short time intervals, and then migrates to other structures [Liu et al., 2014]. The goal of this research is to better understand what determines the spatio-temporal variability of SCR earthquakes.
We argued in a recent paper that “SCR earthquakes are better explained by transient perturbations of local stress or fault strength that release elastic energy from the pre-stressed lithosphere than by the slow accumulation of tectonic stresses on individual faults” [Calais et al., 2016]. In this view, the very slow tectonic loading in SCRs is shared by a system of interacting faults within a crustal volume, such that (1) small, transient, variations can trigger rupture on faults close to failure; and (2) a large rupture on one fault could affect the loading conditions on other faults. It has been proposed that the apparent long-distance roaming of large SCR earthquakes indicates a dynamical system behavior in which change of any part of the system (such as rupture of a fault) could impact nonlinearly the behavior of the whole system [Stein et al., 2011; Liu and Stein, 2016].
Here we propose to test the notion that the spatial and temporal behavior of SCR earthquakes has the characteristics of a nonlinear dynamical system (Zaliapin et al., 2003a,b). The implications are far-reaching since this type of behavior would imply that the concept of recurrence intervals and steady-state strain accumulation and release do not apply to SCR faults. If so, the current practice of seismic hazard assessment in the mid-continental context — based on the assumption of a steady-state system — would need a complete overhaul. This applies in particular to metropolitan France where nuclear infrastructure requires earthquake-resistant design for a 10,000 yr timeframe, a time interval over which stationarity is unlikely.
Pre-requisites: the internship requires background in geophysics or physics, a curiosity about dynamical systems theory, and some knowledge of Unix/Linux and computer programing.
References:
Calais, E., G. Mattioli, C. DeMets, J. M. Nocquet, and S. Stein, “Tectonic strain in plate interiors?,” Nature, vol. 438, pp. E9–E10, 2005.
Calais, E., and S. Stein, “Time-Variable Deformation in the New Madrid Seismic Zone,” Science, vol. 323, no. 5920, pp. 1442–1442, Mar. 2009.
Calais, E., A. M. Freed, R. Van Arsdale, and S. Stein, “Triggering of New Madrid seismicity by late-Pleistocene erosion,” Nature, vol. 466, no. 7306, pp. 608–611, Jul. 2010.
Calais, E., T. Camelbeeck, S. Stein, M. Liu and T.J. Craig, “A new paradigm for large earthquakes in stable continental plate interiors,” Geophys. Res. Lett., in press, 2016.
Liu, M., and S. Stein, “Mid-continental earthquakes: Spatiotemporal occurrences, causes, and hazards,” Earth Science Reviews, vol. 162, pp. 364–386, Nov. 2016.
Liu, M., G. Luo, H. Wang, and S. Stein, “Long aftershock sequences in North China and Central US: implications for hazard assessment in mid-continents,” Earthq. Sci., vol. 27, no. 1, pp. 27–35, Feb. 2014.
S. Stein, M. Liu, E. Calais, and Q. Li, “Mid-Continent Earthquakes as a Complex System,” Seismological Research Letters, vol. 80, no. 4, pp. 551–553, Jul. 2009.
Zaliapin, I., V. Keilis-Borok, and M. Ghil, 2003a: A Boolean delay equation model of colliding cascades. I: Multiple seismic regimes. J. Stat. Phys., vol. 111, pp. 815–837.
Zaliapin, I., V. Keilis-Borok, and M. Ghil, 2003b: A Boolean delay equation model of colliding cascades. II: Prediction of critical transitions. J. Stat. Phys., vol. 111, pp. 839–861.