Megathrusts

Plate boundary faults in subduction zones can generate large earthquakes and tsunamis. Recent studies have revealed that these faults slip in various ways and may be influenced by many factors. Better understanding them should improve hazard assessments.

Geometric and rheological complexities may control the mechanical behaviour of megathrusts, according to an analysis of the heterogeneity in roughness and rock properties of the Middle America megathrust from 3D seismic reflection data.

The morphology and geometry of the plate interface in a subduction zone is heterogeneous and influenced by lower-plate normal faulting, suggests an analysis of seismic data. These properties of subduction interfaces may influence how the largest earthquakes occur.

A transition from rate-weakening to rate-strengthening frictional behaviour with increasing slip rate could explain the observed diversity of slow slip events on faults, according to numerical simulations.

Deformation after large subduction earthquakes reflects the thermal contrast between the mantle wedge and its nose, according to numerical simulations and a synthesis of postseismic uplift data from subduction zones.

Mantle heterogeneity beneath subducting plates may influence giant megathrust earthquakes, according to seismic tomography of the subslab structure beneath six megathrusts that have ruptured in M ≥ 9.0 earthquakes.

A 32-year-long slow-slip event occurred on a shallow part of the Sunda megathrust, perhaps because of stress accumulation after fluid expulsion, according to an analysis of the deformation history of the area and physics-based simulations.

Corals reveal that part of the plate-boundary fault near Sumatra slipped slowly and quietly for three decades before a large earthquake in 1861. The exceptional duration of this slip event has implications for interpreting deformation to assess seismic hazard.

Shallow parts of megathrusts up-dip of locked patches generally have a high slip rate deficit, which could mean tsunami hazard has been underestimated, according to a stress-constrained inversion of geodetic data.

A shallow slow-slip source region has laterally variable elastic properties and pore pressure, and near-velocity-neutral frictional properties, according to seismic imaging of part of the Hikurangi subduction margin and data-constrained modelling.

The transition between the locked and slowly slipping regions of the southern Cascadia megathrust has a lower porosity than these regions, according to seismic imaging. This suggests that the transition area is ductile, which may limit rupture propogation.

Mature parts of the shallow megathrust beneath Costa Rica are characterized by striking corrugations that may channel fluids, according to seismic images. Nascent sections of the subduction zone plate boundary appear only weakly corrugated.

The recurrence time of megathrust earthquakes in Chile may be controlled by frictional contrasts at depth, according to analyses of stress build-up and release related to the December 2016 southern Chile earthquake.

Slow slip events may cause fluids to drain from the plate boundary into the overlying plate at subduction zones, according to seismic analyses of events recorded in Kanto, Japan.

Deformation migrated from depth towards the surface in the months leading up to the 2011 Tohoku-Oki earthquake, according to analyses of satellite gravity data.

Earthquakes that jump from fault to fault in subduction zones can be explained by locking on the plate interface, according to GPS data from New Zealand where the 2016 Kaikoura earthquake produced a complex array of crustal ruptures.

Continuous seismic signal, filtered out by machine-learning methods, could help infer fault displacement in the Cascadia subduction zone.

Stress cycling in subducting crust before and during slow slip events is due to accumulation and release of fluid pressure, according to analysis of small earthquakes in the Hikurangi subduction zone.

Changing stresses and pore fluid pressures during subduction of seamounts, as simulated with a numerical model that couples mechanical and hydrological processes, help explain observed patterns of megathrust slip.

Tsunami generation by megathrust earthquakes is enhanced by extensional faulting in the upper plate when the subducting slab shallows, according to numerical modelling and observations from the Sumatra–Andaman and Tohoku earthquake–tsunami events.