A Parametric Analysis of Fault Reactivation in the New Madrid Seismic Zone: The Role of Pore Fluid Overpressure

Abstract

Earthquakes in Stable Continental Regions (SCR), where localized present-day tectonic loadingis negligible, remain difficult to explain. The New Madrid Seismic Zone (NMSZ) is a type-locale for such events, with four M>7 events in 1811-1812 and a regional seismicity that continues to this day. Here, we seek to determine the most favorable conditions for fault reactivation in such a context using 33 earthquakes in the 2.1-4.7 magnitude range with well-determined focal mechanisms while accounting for the vertical gradient of differential stress with depth. To do so, we developed a Mohr-Coulomb-based parametric analysis of fault reactivation that allows us to vary the orientation of the principal stresses, the shape ratio of the stress tensor, the fault friction coefficient, the pore fluid overpressure, and the gradient of differential stress with depth. Doing so, we are able to determine the lowest stress perturbation conditions required for fault reactivation. Our results show that the reactivation of the faults studied here requires pore fluid overpressure, unless their friction coefficient is 0.4 or less. We argue that such weak faults are unlikely and favor a triggering mechanism via deep fluids, possibly upwelling from the upper mantle where a low-velocity seismic anomaly could indicate their presence. This mechanism, documented in other intraplate areas, does not require local tectonic stress or strain accumulation to explain seismicity in active intraplate regions, where elastic strain is drawn from a prestressed crust.

Characteristics and possible origins of the seismicity in northwestern France

“…Spatial variations of gravitational potential energy on Myr periods [Camelbeeck et al, 2013]; Flexural and isostatic adjustment to erosion and sedimentation on periods ranging from Myr [Champagnac et al, 2007, Vernant et al, 2013 to kyr [Calais et al, 2010]; Flexural and isostatic adjustment to 10-100 kyr glacial cycles [Luttrell andSandwell, 2010, Steffen et al, 2014]; Mechanical response to very short (days to months) hydrological or meteorological transients [e.g. Bollinger et al, 2007, Steer et al, 2014, Leclère and Calais, 2019. Such interactions between tectonics, mass redistributions, and structural inheritance, have been documented in other contexts [e.g.…”

Special issue Comptes-Rendus Geosciences for the 100 years of the BCSF “Seismicity in France”

“…The question of the origin of this seismicity is the subject of various hypotheses and models widely discussed by the scientific community * Corresponding author. [Calais et al, 2016, Leclère and Calais, 2019, Mazzotti et al, 2020. This questioning is based on new measurements made possible by the large-scale equipment launched by Résif in the last ten years.…”