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Subduction megathrusts host the Earth’s greatest earthquakes as the 1960 Valdivia (Mw 9.5, Chile), the largest earthquake instrumentally recorded, and the recent 2004 Sumatra-Andaman (Mw 9.2, Indonesia), 2010 Maule (Mw 8.8, Chile), and 2011 Tohoku-Oki (Mw 9.1, Japan) earthquakes triggering devastating tsunamis and representing a major hazard to society. Unravelling the spatio-temporal pattern of these events is thus a key for seismic hazard assessment of subduction zones. This paper reviews the current state of knowledge of two research areas–empirical analysis of global-scale natural data and experimental data from an analogue seismotectonic modelling—devoted to study cause-effect relationships between subduction zone parameters and the megathrust seismogenic behavior. The combination of the two approaches overcomes the observational bias and inherent sampling limitations of geological processes (i.e., shortness of instrumental and historical data, decreasing completeness and resolution with time into the past) and allows drawing appropriately from multiple disciplines with the aim of highlighting the geodynamic conditions that may favor the occurrence of giant megathrust earthquakes.

The roughness of the subduction interface is thought to influence seismogenic behavior in subduction zones, but a detailed understanding of how such roughness affects the state of stress along the subduction megathrust is still debated. Here, we use seismotectonic analogue models to investigate the effect of subduction interface roughness on seismicity in subduction zones. We compared analogue earthquake source parameters and slip distributions for two roughness endmembers. Models characterized by a very rough interface have lower integrated fault strength and lower interseismic coupling than models with a smooth interface. Overall, ruptures in the rough models have smaller rupture area, duration, and mean displacement. Individual slip distributions indicate a segmentation of the subduction interface by the rough geometry. We propose that flexure of the overriding plate is one of the mechanisms that contribute to a heterogeneous stress distribution, responsible for the observed seismic behavior.Plain Language Summary The largest and most destructive earthquakes on Earth occur along the plate contact in subduction zones, the region where an oceanic plate dives below another plate. The roughness of the downgoing plate, which is a result of the seafloor topography on that plate, is thought to play a role in the occurrence of large subduction earthquakes. With analogue models that include a 3-D-printed seafloor, we test the effect of two types of seafloor roughness on the occurrence of earthquakes: a very rough versus a very smooth seafloor. We observe that the rough seafloor geometry generally hinders the occurrence of large earthquakes along the subduction interface. This finding helps us to highlight where large future earthquakes are more likely to occur.

Correlations between geodynamic parameters and interplate seismicity characteristics in subduction zones are generally weak due to the short instrumental record and multiparameter influences. To investigate the role of subduction velocity Vs and the width of the seismogenic zone W on maximum magnitude Mmax, seismic rate τ, characteristic recurrence rate τc, and moment release rate MRR, we use synthetic data sets from simplified analog and numerical models to gain insight into natural subduction zones seismicity. Our models suggest that Mmax increases with W and is unaffected by Vs, τ increases with Vs, τc increases with Vs/W, and MRR increases with Vs × W. In nature, only the positive correlation between Vs and τ is significant. Random sampling of our time series suggest that the positive correlation between Vs and τ can be observed with short observation time windows. Other correlations, including Mmax versus W, become clear only for time window lengths longer than 1/τc.

Experimental modeling is a methodology used for a wide range of scientific applications, including the study of tectonic processes. This contribution is devoted to provide an overview of laboratory models realized to understand the physics behind the behavior of convergent margins at the mantle scale, focusing on the overall process controlled by the lithosphere–mantle interaction.

Subduction megathrust earthquakes occur at the interface between the subducting and overriding plates. These hazardous phenomena are only partially understood because of the absence of direct observations, the restriction of the instrumental seismic record to the past century, and the limited resolution/completeness of historical to geological archives. To overcome these restrictions, modeling has become a key-tool to study megathrust earthquakes. We present a novel model to investigate the seismic cycle at subduction thrusts using complementary analog (paper 1) and numerical (paper 2) approaches. Here we introduce a simple scaled gelatin-on-sandpaper setup including realistic tectonic loading, spontaneous rupture nucleation, and viscoelastic response of the lithosphere. Particle image velocimetry allows to derive model deformation and earthquake source parameters. Analog earthquakes are characterized by "quasi-periodic" recurrence. Consistent with elastic theory, the interseismic stage shows rearward motion, subsidence in the outer wedge and uplift of the "coastal area" as a response of locked plate interface at shallow depth. The coseismic stage exhibits order of magnitude higher velocities and reversal of the interseismic deformation pattern in the seaward direction, subsidence of the coastal area, and uplift in the outer wedge. Like natural earthquakes, analog earthquakes generally nucleate in the deeper portion of the rupture area and preferentially propagate upward in a crack-like fashion. Scaled rupture width-slip proportionality and seismic moment-duration scaling verifies dynamic similarities with earthquakes. Experimental repeatability is statistically verified. Comparing analog results with natural observations, we conclude that this technique is suitable for investigating the parameter space influencing the subduction interplate seismic cycle. © 2012. American Geophysical Union. All Rights Reserved.

[1] The physics governing the seismic cycle at seismically active subduction zones remains poorly understood due to restricted direct observations in time and space. To investigate subduction zone dynamics and associated interplate seismicity, we validate a continuum, visco-elasto-plastic numerical model with a new laboratory approach (Paper 1). The analogous laboratory setup includes a visco-elastic gelatin wedge underthrusted by a rigid plate with defined velocity-weakening and -strengthening regions. Our geodynamic simulation approach includes velocity-weakening friction to spontaneously generate a series of fast frictional instabilities that correspond to analog earthquakes. A match between numerical and laboratory source parameters is obtained when velocity-strengthening is applied in the aseismic regions to stabilize the rupture. Spontaneous evolution of absolute stresses leads to nucleation by coalescence of neighboring patches, mainly occurring at evolving asperities near the seismogenic zone limits. Consequently, a crack-, or occasionally even pulse-like, rupture propagates toward the opposite side of the seismogenic zone by increasing stresses ahead of its rupture front, until it arrests on a barrier. The resulting surface displacements qualitatively agree with geodetic observations and show landward and, from near the downdip limit, upward interseismic motions. These are rebound and reversed coseismically. This slip increases adjacent stresses, which are relaxed postseismically by afterslip and thereby produce persistent seaward motions. The wide range of observed physical phenomena, including back-propagation and repeated slip, and the agreement with laboratory results demonstrate that visco-elasto-plastic geodynamic models with rate-dependent friction form a new tool that can greatly contribute to our understanding of the seismic cycle at subduction zones.

International audience; The role of seafloor roughness on the seismogenic behavior of subduction zones has been increasingly addressed over the past years, although their exact relationship remains unclear. Do subducting features like seamounts, fracture zones, or submarine ridges act as barriers, preventing ruptures from propagating, or do they initiate megathrust earthquakes instead? We address this question using a global approach, taking into account all oceanic subduction zones and a 117-year time window of megathrust earthquake recording. We first compile a global database, SubQuake, that provides the location of a rupture epicenter, the overall rupture area, and the region where the largest displacement occurs (the seismic asperity) for M W ≥ 7.5 subduction interplate earthquakes. With these data, we made a quantitative comparison with the seafloor roughness seaward of the trench, which is assumed to be a reasonable proxy for the subduction interface roughness. We compare the spatial occurrence of megathrust ruptures, seismic asperities, and epicenters, with two roughness parameters: the short-wavelength roughness R SW (12-20 km) and the long-wavelength roughness R LW (80-100 km). We observe that ruptures with M W ≥ 7.5 tend to occur preferentially on smooth subducting seafloor at long wavelengths, which is especially clear for the M W > 8.5 events. At both short and long wavelengths, seismic asperities show a more amplified relation with smooth seafloor than rupture segments in general. For the epicenter correlation, we see a slight difference in roughness signal, which suggests that there might be a physical relationship between rupture nucleation and subduction interface roughness. Plain Language Summary Subduction zones are regions on Earth where an oceanic plate dives below another plate. Earthquakes that occur along the contact between plates in such regions are among the largest and most destructive on Earth. To better understand where these large earthquakes are most likely to occur, we look at the effect of seafloor roughness. A rough seafloor is often characterized by many topographic features, such as seamounts or ridges, while a smooth seafloor is generally more flat. On a global scale, we compared the roughness of the incoming seafloor of the downgoing plate, with the occurrence of large earthquakes in each subduction zone. We find that the seafloor in front of large earthquakes is generally smoother than in areas where no large earthquakes have occurred. This is the clearest for very large earthquakes, with magnitudes larger than 8.5. Investigating which parameters play a role in the location of earthquakes helps us to understand where future earthquakes are more likely to occur.