Valère Lambert

Contribution of viscoelastic flow in earthquake cycles within the lithosphere-asthenosphere system†

Faults slip relaxes lithospheric stress imposed by mantle flow, and in turn transfers stress to the ductile regions. The interplay of these systems governs the style of deformation at plate boundaries including the recurrence of seismic events. However, such deep processes remain challenging to incorporate in numerical simulations of earthquake cycles. Here, we propose a model that couples fault slip and viscoelastic deformation to simulate fault dynamics in the lithosphere-asthenosphere system. Our method resolves all phases of the earthquake cycle, including dynamic rupture propagation, afterslip, slow-slip events and the modulation of strain rate incurred in the ductile regions. Transient strain accelerations in the asthenosphere may follow both earthquakes and slow-slip events shortly after the rupture, depending on the rheology of the upper mantle and the magnitude of the event. This study opens the door to greater insight into the variability of earthquake cycles by incorporating the dynamics of distributed deformation.

Imaging the distribution of transient viscosity after the 2016 Mw 7.1 Kumamoto earthquake

Crustal rock strength from outer space The response of crustal rock to stresses is challenging to estimate yet vital for determining risks from events such as earthquakes. Moore et al. take advantage of the recent Mw 7.1 Kumamoto earthquake in Japan to determine the rheology of crustal rocks in the region. The observed inversion of the crustal strain rates demonstrates that certain areas have stiff rock and others (e.g., under the Aso volcanic complex) have much weaker rock. The results match up with expectations, which means that the method can successfully measure rock properties over a wide range of strength and large spatial and temporal scales. Science, this issue p. 163 The combination of GPS and InSAR data after the Kumamoto earthquake in Japan allows for an estimate of regional rock rheology. The deformation of mantle and crustal rocks in response to stress plays a crucial role in the distribution of seismic and volcanic hazards, controlling tectonic processes ranging from continental drift to earthquake triggering. However, the spatial variation of these dynamic properties is poorly understood as they are difficult to measure. We exploited the large stress perturbation incurred by the 2016 earthquake sequence in Kumamoto, Japan, to directly image localized and distributed deformation. The earthquakes illuminated distinct regions of low effective viscosity in the lower crust, notably beneath the Mount Aso and Mount Kuju volcanoes, surrounded by larger-scale variations of viscosity across the back-arc. This study demonstrates a new potential for geodesy to directly probe rock rheology in situ across many spatial and temporal scales.

Displacement and Stress Associated with Distributed Anelastic Deformation in a Half‐Space

We present a suite of analytical and semianalytical solutions for the displacements, strains, and stress due to distributed anelastic deformation of finite strain volumes in a half‐space for cuboid sources. We provide the solutions in the cases of antiplane strain, plane strain, and 3D deformation. These expressions represent powerful tools for the analysis of deformation data to image distributed strain in the Earth’s interior and for the dynamic modeling of distributed deformation off faults, including thermoelasticity, poroelasticity, and viscoelasticity. We include computer programs that evaluate these expressions free of major singular points. Combined with formulas that describe the deformation around faults, these solutions represent a comprehensive description of quasi‐static deformation throughout the earthquake cycle within the lithosphere–asthenosphere system. [Electronic Supplement:][1]Animations of displacement and stress. [1]: http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120160237/-/DC1