The seismic cycle at subduction thrusts: Insights from seismo‐thermo‐mechanical models

Abstract

[1] The underestimation of the size of recent megathrust earthquakes illustrates our limited understanding of their spatiotemporal occurrence and governing physics. To unravel their relation to associated subduction dynamics and long-term deformation, we developed a 2-D continuum viscoelastoplastic model that uses an Eulerian-Lagrangian finite difference framework with similar on-and off-fault physics. We extend the validation of this numerical tool to a realistic subduction zone setting that resembles Southern Chile. The resulting quasi-periodic pattern of quasi-characteristic M8-M9 megathrust events compares quantitatively with observed recurrence and earthquake source parameters, albeit at very slow coseismic speeds. Without any data fitting, surface displacements agree with GPS data recorded before and during the 2010 M8.8 Maule earthquake, including the presence of a second-order flexural bulge. These surface displacements show cycle-to-cycle variations of slip deficits, which overall accommodate 5% of permanent internal shortening. We find that thermally (and stress) driven creep governs a spontaneous conditionally stable downdip transition zone between temperatures of 350 ı C and 450 ı C. Ruptures initiate above it (and below the forearc Moho), propagate within it, interspersed by small intermittent events, and arrest below it as ductile shearing relaxes stresses. Ruptures typically propagate upward along lithological boundaries and widen as pressures drop. The main thrust is constrained to be weak due to fluid-induced weakening required to sustain regular subduction and to generate events with natural characteristics (fluid pressures of 75-99% of solid pressures). The agreement with a range of seismological, geodetic, and geological observations demonstrates the validity and strength of this physically consistent seismo-thermo-mechanical approach.

Modeling Seismic Cycles of Great Megathrust Earthquakes Across the Scales With Focus at Postseismic Phase

“…Presently, modeling of the long-term (millions of years' time scale) deformation at plate boundaries (e.g., Baes et al, 2016;Burov et al, 2014;Gerya, 2011;Popov et al, 2012;Quinteros & Sobolev, 2013) and modeling of earthquakes and their seismic cycles (e.g., Barbot et al, 2012;Lambert & Barbot, 2016;Liu & Rice, 2007;Rice, 1993;Rice & Ben-Zion, 1996) are independent. A few models (Sobolev & Babeyko, 2004;van Dinther et al, 2013avan Dinther et al, , 2013bvan Dinther et al, , 2014 attempted to close the gap between these temporal scales, but these studies were limited to a minimum time resolution of several years. In particular, van Dinther et al (2013b) complemented a long-term geodynamic model of subduction by the rate-weakening friction law at the subduction plate interface, which allowed simulation of seismic cycles.…”

“…A few models (Sobolev & Babeyko, 2004;van Dinther et al, 2013avan Dinther et al, , 2013bvan Dinther et al, , 2014 attempted to close the gap between these temporal scales, but these studies were limited to a minimum time resolution of several years. In particular, van Dinther et al (2013b) complemented a long-term geodynamic model of subduction by the rate-weakening friction law at the subduction plate interface, which allowed simulation of seismic cycles. However, due to technical reasons, ''rupture propagation'' in that model lasted more than a decade.…”

“…In particular, a longstanding challenge has been to model earthquakes in a self-consistent way as a part of a seismic cycle (Wang et al, 2012). In addition, most of the recent seismic-cycle models with several exceptions (Freed & B€ urgmann, 2004;Freed et al, 2006Freed et al, , 2007Freed et al, , 2010Freed et al, , 2012Lambert & Barbot, 2016;Masuti et al, 2016;van Dinther et al, 2013b) use simplified linear rheological models, such as Burger's rheology (see review Wang et al, 2012, and references therein), that are not based on mineral-physics laboratory data.…”

Interseismic deformation at subduction zones investigated by 2D numerical modeling: case study before the 2010 Maule earthquake

“…Our study shows that in order to retrieve appropriately the mechanical processes in play during interseismic deformation, numerical models should account for the effects of plate f lexure, thus pointing to the perspective of integrating both short-term and long-term approaches (e.g., Van Dinther et al, 2013). Meanwhile, the careful application of locally reduced basal velocities in an ESPM approach offers a more realistic treatment of GPS interseismic surface displacements than the conventional BSM approach.…”

A megathrust earthquake cycle model for Northeast Japan: bridging the mismatch between geological uplift and geodetic subsidence

“…As Hashimoto et al (2008) discussed, this shortfall may be due to indirect effects such as crustal thickening due to horizontal shortening and possible magmatic underplating, which expectedly causes uplift (e.g., Tajikara 2004;Ikeda 2014). Another possibility might be plastic deformation within the lithosphere during the interseismic stage that accumulates over multiple earthquake cycles (van Dinther et al 2013). …”