Influence of Farallon Slab Loading on Intraplate Stress and Seismicity in Eastern North America in the Presence of Pre‐Existing Weak Zones

Abstract

Despite the stability of the continental interior, eastern North America has hosted many significant historical earthquakes. Seismicity concentrates within tectonically inherited structures, which can act as weak zones where stress accumulates. Within these zones, systematic stress rotations may be explained by long‐wavelength sources. We test the hypothesis that mantle‐flow driven by the Farallon slab contributes to intraplate seismicity via the reactivation of pre‐existing faults. We model the stress field using seismically constrained global high‐resolution finite‐element flow models with CitcomS. To isolate the slab's effect, we vary its buoyancy between a case of neutrality and a case with full negative thermal buoyancy derived from tomography. Low‐viscosity lithospheric weak zones located at failed rifts, loaded by a mass anomaly at depth, transmit elevated stresses to the overlying crust. The sinking of the Farallon slab drives localized mantle flow beneath the central‐eastern US, generating a large stress amplification of 100–150 MPa peaking over the New Madrid Seismic Zone (NMSZ). This stress amplification exerts a continent‐wide clockwise rotation on the stress field, which in the presence of weak zones reproduces some observed deviations of the seismically inferred SHmax from the regional borehole SHmax, bringing optimally oriented faults, closer to failure, some of which are associated with major historical earthquakes, including the Reelfoot Fault in the NMSZ and the Timiskaming Fault in Western Quebec. However, stronger lithospheric viscosity gradients, shallower weak zones, or weaker faults are still needed to fully reproduce the observed stress field in some areas.