Res. Earth Planet. 1 and references. https://doi.org/10.1038/s41561-021-00863-5, DOI: https://doi.org/10.1038/s41561-021-00863-5. 14, 33153323 (2013). Soc. The fluids move through the system by a variety of pathways, including faults, fractures, and permeable strata within the megathrust and overriding plate (e.g., Carson and Screaton, 1998), or they remain trapped by low-permeability sediments, affecting the seismogenic zone by increasing fluid pressures (e.g., Saffer and Bekins, 2002). 11) and Marianas (Fig. Offshore geodetic monitoring will provide critical information about the along-dip and near-trench strain accumulation process and the occurrence of shallow slow-slip events and stable sliding that may prevent strain buildup. volume15,pages 6773 (2022)Cite this article. Wollherr, S., Gabriel, A.-A. Extended Data Fig. The red line is the vertical seafloor uplift (not to scale, amplified200). Shearer, P. & Brgmann, R. Lessons learned from the 2004 SumatraAndaman megathrust rupture. The 20062007 Kuril Islands sequence is another example of coupled great earthquakes, although with diverse focal mechanisms. Noda, H. & Lapusta, N. Stable creeping fault segments can become destructive as a result of dynamic weakening. Nat. These were also initially observed in the vicinity of the deepest portions of the seismogenic zone (Fig. Megathrust roughness and structural complexity are thought to be controls on earthquake slip at subduction zones because they result in heterogeneity in shear strength and resolved stress.. (2014) attributed along-strike variability in seismic reflection characteristics along the Nankai subduction zone to differences in fluid amounts along the megathrust. Am. Megathrust ruptures involve thrusting of subducting. Lett. Gabriel, A.-A., Ampuero, J.-P., Dalguer, L. A. Some solutions are well resolved, others have severe trade-offs between kinematic constraints and model parameterization. Along the central Kuril Islands, the 2006 Mw 8.3 earthquake ruptured a portion of the megathrust between the 1963 Mw 8.5 and 1952 Mw 9 earthquakes identified as a seismic gap that may have partially failed in 1918 (e.g., Lay et al., 2009). (2017) describes GPS data analysis that supports the presence of a slow slip event in the 2014 Iquique region during the 8 mo prior to the main shock. 29th International Conference ISC 2014 (eds Kunkel, J. M. et al.) Sci. Red waveforms are computed using the base scenario, while blue waveforms correspond to the model featuring less off-fault yielding and more slip to the trench, yet, indistinguishable synthetics, shown in Fig. As demonstrated in the previous section, earthquake observations now span a wide range of slip speed and complexity. Here, we collate the latest research and opinion articles in. Synthetics are generated using Instaseis103 and the PREM model including anisotropic effects and a maximum period of 10 s. (b) Locations at which synthetic data are compared with observed records. Geophys. 97, S86S102 (2007). pr63qo and pr45fi). Socquet et al. Res. Seismol. An historical great event in 1788 ruptured the 1938 zone and Kodiak Island portions of the 1964 ruptures (e.g., Briggs et al., 2014), indicating that boundaries between recent ruptures have not been persistent. The movement between continental and oceanic plates at the bottom of the sea, so-called megathrust earthquakes, generates the strongest tremors and the most dangerous tsunamis. Res. Due to their size and frequent occurrence, earthquakes on megathrust faults constitute significant seismic and tsunami hazards in subduction zones around the world. Lett. Lett. & Satake, K. Tsunami source of the 2004 SumatraAndaman earthquake inferred from tide gauge and satellite data. Nanayama, F. et al. The tsunami animations show the predicted evolution of the sea surface height amplitudes (in metres). Similarly, correlations between large negative trench-parallel gravity anomalies and the locations of great earthquakes may also connect forearc structure with megathrust processes (Song and Simons, 2003). [1][2] Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes.[3]. Wollherr, S., Gabriel, A.-A. To obtain Earth Planet. Abstr. Aftershocks occur off of the main megathrust rupture plane as well. Ulrich, T., Gabriel, AA. (b,d): vertical displacements. It is also difficult to establish the updip limit of rupture in large megathrust ruptures to judge whether there is potential for tsunami earthquakes to occur subsequently, as occurred in the 2010 Mentawai earthquake updip from the 2007 Sumatra earthquakes. Nat. Geophys. [12], Since the earthquakes associated with these subduction zones deform the ocean floor, they often generate a significant series of tsunami waves. At the slowest end of the slip spectrum, there are slow slip events (SSEs), which are observed geodetically along many subduction zones. Yet another important input into the subduction zone is the overall roughness of the subducting plate. In Proc. Am. Kim, J., Pedersen, G. K., Lvholt, F. & LeVeque, R. J. Other small- to moderate-magnitude earthquakes have produced slip in subducting areas with rough topography. A new digital bathymetric model of the worlds oceans. Front. The Tonga subduction zone includes a shallow peak at 1015 km, and a deeper one at 4045 km; again, the deeper one is likely to be from intraslab compressional events (e.g., Meng et al., 2015b). Laske, G., Masters, G., Ma, Z. Megathrusts are typically locked from less than ten to a few tens of kilometres depth owing to frictional resistance2. (1979), and recent great earthquakes (19792016). Lett. A megathrust earthquake takes place when the fault ruptures, allowing the plates to abruptly move past each other to release the accumulated strain energy. Thrust faults are distinguished from other reverse faults because they dip at a relatively shallow angle, typically less than 45,[8] and show large displacements. The Ye et al. Megathrust roughness and structural complexity are thought to be controls on earthquake slip at subduction zones because they result in heterogeneity in shear strength and resolved stress. The 2011 Tohoku-Oki earthquake: displacement reaching the trench axis. 25, 297356 (1981). S. Bileks research on earthquakes is supported by NSF grant OCE-1434550. We thank S. Wollherr, C. Uphoff, M. Bader, S. Rettenberger, C. Pranger, T. Lay and J. Behrens for fruitful discussion. & Rokosky, J. M. Rev. Focal mechanisms of great earthquakes between 1979 and 2016 are from the Global Centroid Moment Tensor (GCMT) catalog. Animation showing the rupture dynamics of the stronger sediments scenario in terms of absolute slip rate (ms1) across the fault network. 2 The importance of strongly depth-dependent rigidity. Seismic imaging of forearc backthrusts at northern Sumatra subduction zone. Following in the spirit of the sandbox models, Wang and Bilek (2011) presented a conceptual model of strong geometric features such as seamounts significantly deforming the surrounding upper plate with a complex network of fractures, supported by geologic evidence of highly fractured exhumed upper-plate zones, seismic imaging, and recent numerical models (Ding and Lin, 2016). de Linage, C. et al. Pelties, C., de la Puente, J., Ampuero, J.-P., Brietzke, G. B. Res. Res. Res. [22], Compared with other earthquakes of similar magnitude, megathrust earthquakes have a longer duration and slower rupture velocities. Susan L. Bilek, Thorne Lay; Subduction zone megathrust earthquakes. Res. See description of Figure 3 for details. Targeted instrumentation of specific identified seismic gaps prior to great earthquakes in 2010, 2014, and 2015 along Chile, in 2005 and 2007 along Sumatra, in 2016 along Ecuador, and in other locations, has resulted in unprecedented seismic and geodetic data sets for recent events. We also used the GCMT Mw-frequency relations for Mc = 5.2 to evaluate overall seismic productivity variations during the 19762016 time period using both the full set of events, as well as only thrust faulting events. Earth Planet. Geophys. These variations in fluid content and pressure are also linked to variations in slip processes. In contrast, the Chile, Peru, Sumatra, Alaska, and Cascadia subduction zones have higher normal forces and plate coupling. Singh, S. C. et al. (2016) presented coupling estimates based on offshore measurements, suggesting wide areas of the shallow Nankai subduction zone have high slip deficit and are strongly locked, which expands the regions where shallow, tsunamigenic slip is possible. Observations of slip processes for subduction zone megathrusts have expanded greatly beyond early measurements of earthquake rupture front velocities, which were on the order of 75%95% of the shear wave velocity in the slip zone expansion of the earthquake (e.g., Kanamori and Brodsky, 2004). (b) and (c) Off-fault plastic strain (quantified as , Eq. Science 308, 15961596 (2005). Here, we focus on megathrust faulting, which produces the greatest hazards. There is another peak in the Kuril zone that is much deeper, between 60 and 65 km, although the corresponding thrust-mechanism events have strikes inconsistent with the local trench orientation, so they are likely intraslab events. Subduction megathrust heterogeneity characterized from 3D seismic data. considers the deeper sector beneath the seismogenic zone of the southernmost part of the Cascadia megathrust, and establishes that this transition zone has a ductile rheology, which should restrict the area that can slip rapidly and thereby the largest possible earthquake magnitude. Because high fluid pressure acts to reduce effective normal stress, fluids play an important role in the earthquake process. Hardebeck, J. L. & Hauksson, E. Crustal stress field in Southern California and its implications for fault mechanics. Geophys. 97, S152S173 (2007). (2012) found evidence for small-magnitude earthquake clusters in areas of subducted seamounts along the Cascadia subduction zone. Tobin, H. J. Megathrusts exhumed. Google Scholar. [4][5] However, the term is also occasionally applied to large thrust faults in continental collision zones, such as the Himalayan megathrust. Thrust faulting earthquake distribution and Mw-frequency distributions for the Peru subduction zone from the Global Centroid Moment Tensor (GCMT) catalog. SSEs are often, but not always, accompanied by nonvolcanic tremors and are grouped into the episodic tremor and slip (ETS) category (e.g., Dragert et al., 2001; Kostoglodov et al., 2003; Obara et al., 2004; Hirose and Obara, 2006; Schwartz and Rokosky, 2007; Beroza and Ide, 2011). Ishii, M., Shearer, P. M., Houston, H. & Vidale, J. E. Extent, duration and speed of the 2004 SumatraAndaman earthquake imaged by the Hi-Net array. Similarly, Ye et al. Nature 424, 660663 (2003). From large seamounts entering the Japan Trench (e.g., Nishizawa et al., 2009), to smaller seamounts leaving scars in the forearc in Costa Rica (e.g., Ranero and von Huene, 2000), and large seamounts and ridges entering the subduction zone along Peru, Chile, and elsewhere (e.g., Spence et al., 1999; Robinson et al., 2006; Sparkes et al., 2010; Marcaillou et al., 2016), these features are significant enough to likely affect megathrust earthquakes, although exactly how is an active debate. J. Geophys. Pure Appl. Our compilations of these various global studies also suggest weak depth dependence in both ER/M0 and stress drop, with large scatter (Figs. They found additional energy-deficient events in the rupture zones of the 1992 Nicaragua and 2006 Java tsunami earthquakes. In the far-field a different scaling is applied. The greatly expanded cabled S-net offshore Honshu now provides continuous monitoring of moderate-slip earthquakes, and data assimilation methods will enable early tsunami warning of unprecedented quality. Nakajima and Hasegawa (2016) found gaps in LFE occurrence in areas where they observed small Vp and Vs anomalies, indicative of a well-drained and low-pore-pressure megathrust; the LFEs are instead concentrated in areas of higher Vp and Vs anomalies, serving as proxies for higher-pore-fluid pressure. In recent decades, many observations have indicated depth dependence along megathrusts for a variety of seismic characteristics. Earth Planets Space 63, 761765 (2011). Earth. Other great shallow events in the region in 1917 (Kermadec, M 8.2), 1919 (Tonga, M 8.1), and 1917 (Samoa, M 8.0) all appear to have been intraplate events (Meng et al., 2015b). All of these deformation processes can produce hazards, from seismic shaking to submarine slumping and tsunami generation. Great (Mw 8.0) megathrust earthquakes and the subduction of excess sediment and bathymetrically smooth seafloor. Fujii, Y. Great earthquakes on megathrusts occur in irregular cycles of interseismic strain accumulation, foreshock activity, main-shock rupture, postseismic slip, viscoelastic relaxation, and fault healing, with all stages now being captured by geophysical monitoring. Schwartz, S. Y. When one of the plates is composed of oceanic lithosphere, it dives beneath the other plate (called the overriding plate) and sinks into the Earth's mantle as a slab. Geodesy also enables characterization of upper-plate sliver or block motions that may result from oblique convergence. Denolle and Shearer (2016) examined spectral ratios for over 900 thrust earthquakes (M > 5.5) and found weak dependence of scaled source duration with increasing depth on the fault. Megathrust earthquakes are characterized as large in magnitude, occurring well within plate interiors, and being the most damaging and deadly.. Megathrust earthquakes are some of the most powerful and devastating earthquakes that occur on Earth.They typically occur at subduction zones, where one tectonic plate is forced beneath another. 37, 345366 (2009). Confidence in such assertions must be assessed with caution, and the use of geodetic measurements to assess upper-plate strain is the most promising approach to evaluating actual seismic potential in such regions. There is a weak tendency for high-stress-drop megathrust ruptures with a given moment to have lower aftershock production, which is attributed to the smaller main-shock rupture dimensions (Wetzler et al., 2016). Sediment type is also important for controlling slip behavior. Thrust-faulting earthquake distribution and Mw-frequency distributions for the Chile subduction zone from the Global Centroid Moment Tensor (GCMT) catalog. Along the northern Japan subduction zone, Tormann et al. Similar to the depth dependence of source duration discussed in the Source Duration subsection herein, Denolle and Shearer (2016) found very weak depth dependence for stress drop and scaled energy using their global catalog. Harris, R. A. et al. Rushing and Lay (2012) examined the differences between mb and Mw for a large catalog of likely megathrust events with Mw 5 in several subduction zones (Chile, Japan, Sumatra, Kuril, Aleutians, Sumba, Peru). In many cases, these LFEs occur as swarms that comprise much of the seismic nonvolcanic tremor observed in subduction zone settings (e.g., Ide et al., 2007b). Guilbert, J. Wells et al. Wirp, S. A. et al. Extended Data Fig. Examples of tremor and slow-slip events (SSE) located at the downdip portion of the seismogenic zone, modified from Beroza and Ide (2011). Examples of range of outer-rise seismicity characteristics following large and great megathrust earthquake ruptures, reprinted from Sladen and Trevisan (2018), with permission from Elsevier. (2015a, 2015b) demonstrated that samples of the smectite-rich fault material obtained from the shallow drilling of the 2011 Tohoku earthquake zone can deform in the laboratory at a variety of rates, from fast seismic slip to slow SSE speeds, to produce the range of slip behaviors observed in that zone. The source dimensions of the main slip zone for the 2014 Iquique event were indeed unusually small for a great earthquake. (2013) also focused on regional comparisons, finding weak to no correlation between longer duration and reported amounts of subducted sediment, presence of bathymetric features, or regions of observed afterslip, all factors that have been proposed to affect rupture complexity and duration. In some cases, such as for the 1837 and 1737 events in the 1960 Chile rupture zone, the size of the historic events is being reevaluated based on detailed examination of the record, modifying inferences of segmentation and regularity (e.g., Cisternas et al., 2017). The Tonga subduction zone has b values of 0.92 and 0.93 for the full data set and the megathrust, respectively, while the sparse Marianas data set has corresponding b values of 1.03 and 1.07, respectively. (2016b) study included only megathrust ruptures; group 1 events are those with independent rupture model constraints; rupture characteristics for group 2 events were determined using a range of rupture velocities in kinematic inversions of teleseismic body waves. (a),(b) Along arc-variation of rupture velocity of two scenarios yielding stronger (a) or weaker (b) sediments compared to observational inferences from Rayleigh48 and acoustic waves49. Cumulative seismic moment release with depth in the indicated subduction zones. Geophys. Animation showing the rupture dynamics of the base and PREM earthquake scenarios in terms of absolute slip rate (ms1) across the fault network, side by side (left: base; right: PREM scenario). Very shallow megathrust slip also occurred in the 2006 Mw 8.3 Kuril earthquake, an area also lacking in previous interplate seismicity (Ammon et al., 2008; Lay et al., 2009). 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