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Subducting seamounts are recognized as one of the key features influencing megathrust earthquakes. However, whether they trigger or arrest ruptures remains debated. Here, we use analog models to study the influence of a single seamount on megathrust earthquakes, separating the effect of topography from that of friction. Four different model configurations have been developed (i.e., flat interface, high and low friction seamount, low friction patch). In our models, the seamount reduces recurrence time, interseismic coupling, and fault strength, suggesting that it acts as a barrier: 80% of the ruptures concentrate in flat regions that surround the seamount and only smaller magnitude earthquakes nucleate above it. The low‐friction zone, which mimics the fluid accumulation or the establishment of fracture systems in natural cases, seems to be the most efficient in arresting rupture propagation in our experimental setting. Plain Language Summary: Seamounts ‐ extinct volcanoes ‐ are ubiquitous features of the seafloor of subducting plates. During their descent toward the mantle, seamounts are squeezed between the overriding‐ and subducting plates, creating a geometrical and mechanical discontinuity that is thought to control the largest earthquakes that occur on Earth. It is not known, however, whether they trigger or arrest earthquakes, as a variety of observations have been used to support one or the other hypothesis. Here, we tackle this subject using scaled laboratory models that allow reproduction of large earthquakes. Our models support a scenario where subducting seamounts primarily arrest rupture propagation, limiting therefore expected maximum magnitudes. Our models also suggest that subducting seamounts might influence the recurrence time of large earthquakes by decreasing their frequency. Key Points: We investigated the effect of seamount subduction on megathrust earthquakes by isolating the role of geometry from that of frictionSeamounts act primarily as barriers to earthquake propagation, promoting small ruptures and decreasing seismic couplingReduced friction displays maximum barrier efficiency, a configuration likely associated with fluids or fracture systems in nature [ABSTRACT FROM AUTHOR]

Although a high prevalence of COVID-19-associated pulmonary aspergillosis has been reported, it is still difficult to distinguish between colonization with Aspergillus fumigatus and infection. Concomitantly, similarities between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and hypersensitivity pneumonitis were suggested. The objective of this study was to investigate retrospectively if precipitin assays targeting A. fumigatus could have been useful in the management of SARS-CoV-2 patients hospitalized in an Intensive Care Unit (ICU) in 2020. SARS-CoV-2 ICU patients were screened for Aspergillus co-infection using biomarkers (galactomannan antigen, qPCR) and culture of respiratory samples (tracheal aspirates and bronchoalveolar lavage). For all these patients, clinical data, ICU characteristics and microbial results were collected. Electrosyneresis assays were performed using commercial A. fumigatus somatic and metabolic antigens. ELISA were performed using in-house A. fumigatus purified antigen and recombinant antigens. Our study population consisted of 65 predominantly male patients, with a median ICU stay of 22 days, and a global survival rate of 62%. Thirty-five patients had at least one positive marker for Aspergillus species detection. The number of arcs obtained by electrosyneresis using the somatic A. fumigatus antigen was significantly higher for these 35 SARS-CoV-2 ICU patients (P 0.01, Welch's t -test). Our study showed that SARS-CoV-2 ICU patients with a positive marker for Aspergillus species detection more often presented precipitins towards A. fumigatus. Serology assays could be an additional tool to assess the clinical relevance of the Aspergillus species in respiratory samples of SARS-CoV-2 ICU patients. Lay Summary This study showed retrospectively that precipitin assays, such as electrosyneresis, could be helpful to distinguish between colonization and infection with Aspergillus fumigatus during the management of severe acute respiratory syndrome Coronavirus-2 (SARS CoV-2) patients in an intensive care unit. [ABSTRACT FROM AUTHOR]

Based on 2D seismic profiles, multibeam and seabed grab cores acquired during the Garanti cruise in 2017, 1–5 km wide seabed giant polygons were identified in the Grenada basin, covering a total area of ∼55,000 km2, which is the largest area of outcropping polygonal faults (PF) ever found on Earth so far. They represent the top part of an active 700–1,200 m thick underlying polygonal fault system (PFS) formed due to the volumetric contraction of clay‐ and smectite‐rich sediments, initiated in the sub‐surface at the transition between the Early to Middle Pliocene. The short axes of the best‐fit ellipses obtained from a graphical center‐to‐center method were interpreted as the local orientation of a preferential contraction perpendicular to the creep deformation of slope sediments. In the North Grenada Basin, the polygons are relatively regular, but their short axes seem to be parallel to a N40°E extension recently evidenced in the forearc, possibly extending in the backarc, but not shown in the study area. They are most probably related to a progressive burial due to a homogeneous subsidence. In the South Grenada Basin, the polygons are more elongated and their axes are progressively rotating southeastward toward the depocenter, indicating a creep deformation toward the center of the basin created by a differential subsidence. Seabed polygons and underlying PF could thus be indicative of the deformation regime of shallow sediments related to main slopes controlled by two different basin architectures. Key Points: Seabed giant polygons in the Grenada Basin cover the largest area (55,000 km2) ever found on EarthThe short axis of best‐fit ellipses of polygons may represent the orientation of the creep deformation of slope sedimentsThe north and south tectonic domains in the Grenada Basin are marked by major differences in the shape and orientation of seabed polygons [ABSTRACT FROM AUTHOR]

The Eocene tectonic evolution of the easternmost Caribbean Plate (CP) boundary, that is the Lesser Antilles subduction zone (LASZ), is debated. Recents works shed light on a peculiar period of tectonic duality in the arc/back-arc regions. A compressional-to-transpressional regime occurred in the north, while rifting and seafloor spreading occurred in Grenada basin to the south. The mechanism for this strong spatial variation and its evolution through time has yet to be established. Here, using 3-D subduction mechanical models, we evaluate whether the change in the trench-curvature radius at the northeast corner of the CP could have modulated the duality. We assume asymmetrical CP boundaries at the north (from east to west: oblique subduction to strike-slip) and at the south (subduction-transform edge propagator-like behavior). Regardless of the imposed trench curvature, the southern half of our modeled CP undergoes a NW-to-W-oriented extension due to the tendency of the southernmost part of the South-America oceanic slab to rollback. In contrast, the tectonic regime in the northeast corner of the CP depends on the trench-curvature radius. A low radius promotes transtension-to-transpression, with a NE-oriented compressive component of the principal stress. A high radius largely reduces the compressive component and promotes an extensional regime similar to that in the south. We thus propose that an initially low-curvature radius of the NE-LASZ triggered the tectonic N-S duality in the Eocene and led to an ephemeral period of transpression/compression at the north. However, an additional mechanism might have been required to locally enhance compression. [ABSTRACT FROM AUTHOR]

Oblique collision of buoyant provinces against subduction zones frequently results in individualizing and rotating regional‐scale blocks. In contrast, the collision of the Bahamas Bank against the Northeastern Caribbean Plate increased the margin convexity triggering forearc fragmentation into small‐scale blocks. This deformation results in a prominent sequence of V‐shaped basins that widens trenchward separated by elevated spurs, in the Northern Lesser Antilles (NLA, i.e., Guadeloupe to Virgin Island). In absence of deep structure imaging, various competing models were proposed to account for this Basins‐and‐Spurs System. However, high‐resolution bathymetric and deep multichannel seismic data acquired during cruises ANTITHESIS 1‐3, reveal a drastically different tectonic evolution of the NLA Forearc. During Eocene‐Oligocene time, the Caribbean Northeastern Boundary accommodated the Bahamas Bank collision and the subsequent margin convex bending by major left‐lateral strike‐slip faults systems in the Greater Antilles and by trench‐parallel extension along N40°–90°‐trending normal faults in the NLA. Block rotations, forearc fracturing, and V‐shaped valleys opening went along with this tectonic phase, which ends up with tectonic uplifts and an earliest‐middle Miocene regional emersion phase. Post middle Miocene regional subsidence and tectonic extension in the forearc are partly accommodated along the newly imaged N300°‐trending, 200‐km‐long normal Tintamarre Faults Zone. This drastic subsidence phase reveals vigorous margin basal erosion, which likely generated the synchronous westward migration of the volcanic arc. Thus, unlike widely accepted previous theoretical models, the NE‐SW faulting and the prominent V‐shaped valleys result from a past and sealed tectonic phase related to the margin bending and subsequent blocks rotation. Key Points: The N. Lesser Antilles has undergone Eocene‐Oligocene NW‐SE extention and post mid Miocene NE‐SW extension separated by a regional emersionFault‐bounded V‐Shaped valleys result from past and sealed NW‐SE extention due to Bahamas Bank collision, margin bending, and blocks rotationDrastic post mid Miocene subsidence and synchronous westward migration of the volcanic arc reveal vigorous subduction‐related margin erosion [ABSTRACT FROM AUTHOR]

Strain partitioning related to oblique plate convergence has long been debated in Northern Lesser Antilles. Geophysical data acquired during the ANTITHESIS cruises highlight that the sinistral strike‐slip Bunce Fault develops along the vertical, long, and linear discontinuity between the sedimentary wedge and a more rigid backstop. The narrowness of the 20‐ to 30‐km‐wide accretionary wedge and its continuity over ~850 km is remarkable. The Bunce Fault extends as far south as 18.5°N where it anastomoses within the accretionary prism where the sharp increase in convergence obliquity possibly acts as a mechanical threshold. Surface traces related to subducting seamounts suggest that 80% of the lateral component of the convergent motion is taken up by internal deformation within the accretionary prism and by the Bunce Fault. The absence of crustal‐scale, long‐term tectonic system south of the Anegada Passage casts doubt upon the degree of strain partitioning in the Northern Lesser Antilles. Plain Language Summary: Lithospheric plates are frequently bounded by subduction zones where oceanic plates underthrust overriding plates. In most cases, this convergence is oblique to the margin, its resulting tectonic deformation is generally due to margin‐normal and margin‐parallel components of the plate convergence vector. At the Northern Lesser Antilles, the North American Plate subducts beneath the Caribbean Plate with oblique convergence increasing from Guadeloupe to Virgin Islands. This study aims to analyze and resolve the tectonic deformation along this margin. We acquired marine geophysical data during ANTITHESIS cruises (2014–2016) to image the seafloor and the crustal structure. We place a particular emphasis on the strike‐slip Bunce Fault, which extends over ~850 km, including a newly discovered 350‐km segment, 20–30 km landward from the trench. Although long strike‐slip faults have already been observed at oblique subduction zones, the proximity of the Bunce Fault to the trench is unprecedented. We conclude that the mechanical discontinuity between the sedimentary wedge and a more rigid backstop and the sharp increase in obliquity is likely to control the location of the trench‐parallel, strike‐slip deformation north of the Anegada Passage when strain partitioning to the south may be small or taken up in more diffuse pattern. Key Points: ANTITHESIS cruises highlight the SE extent of the Bunce Fault where it anastomoses in the prism at the change of obliquity of convergenceThe sinistral strike‐slip Bunce Fault develops along a rheological discontinuity at the prism backstop at 30 km from the trenchA synthesize of structures resulting from strain partitioning observed in the Greater and Northern Lesser Antilles is proposed [ABSTRACT FROM AUTHOR]

The largest compilation of seismological and gravimetry data are combined in a sequential inversion to shed light on unresolved crustal structures in Northern Taiwan and Southernmost Ryukyu area. Our density and seismic velocity models reveal a NW–SE trending Transfer Zone (TZ) between 23.25°N and 24°N. This primary TZ delimits major changes in the Eurasian Plate (EP) slab geometry and dynamics, as well as first order crustal structure variations. North of this TZ, the EP slab is breaking off from north to south as a result of (1) the extreme EP bending favouring plastic deformation, (2) the stretching of the plate caused by the downward pull of the oceanic part of the slab versus the buoyancy of continental part of the plate still deforming in the Taiwan orogen and (3) the indentation of the EP slab by the western slab edge of the Philippine Sea Plate (PSP). The change of EP slab dip angle is clearly observed in the density profiles. The subvertical northernmost tip of EP slab allows asthenospheric upwelling through slab tear and subsequent invasion of the region beneath the Longitudinal Valley. This process is migrating southward up to the TZ, which marks the transition to a different rheological behaviour. The combination of deep arc-continent collision, clockwise asthenospheric toroidal flow and westward propagation of the southern Okinawa rift results in a 100° clockwise rotation of the northernmost tip of the Central Range. The eastward extrusion of this crustal block (∼90 km in diameter) overlays and deflects the PSP slab. The indentation of the EP by the PSP (Luzon Arc) thus results in complex lithospheric accommodation processes and structures. [ABSTRACT FROM AUTHOR]

Despite the growing spatiotemporal density of geophysical observations at subduction zones, predicting the timing and size of future earthquakes remains a challenge. Here we simulate multiple seismic cycles in a laboratory‐scale subduction zone. The model creates both partial and full margin ruptures, simulating magnitude Mw 6.2–8.3 earthquakes with a coefficient of variation in recurrence intervals of 0.5, similar to real subduction zones. We show that the common procedure of estimating the next earthquake size from slip‐deficit is unreliable. On the contrary, machine learning predicts well the timing and size of laboratory earthquakes by reconstructing and properly interpreting the spatiotemporally complex loading history of the system. These results promise substantial progress in real earthquake forecasting, as they suggest that the complex motion recorded by geodesists at subduction zones might be diagnostic of earthquake imminence. Plain Language Summary: Large and devastating subduction earthquakes, such as the 2011 magnitude 9.0 Tohoku‐oki earthquake (Japan), are currently considered unpredictable. Scientists lack a long enough seismic catalog that is necessary for drawing statistical insights and developing predictions. For this reason, we simulate tens of earthquakes using a small‐scale experimental replica of a subduction zone. We show that machine learning (a group of algorithms that make predictions based on the "information" acquired in past "experience") can predict when, where, and how big the next experimental earthquake will be. The "information" in our study is provided by the slow deformation accumulating in the analog tectonic plates during the periods in between earthquakes. Since such slow deformation is also measured by means of space geodesy along real subduction zones, there is the possibility that, in the future, variations of this machine learning approach can predict the timing and size of natural subduction earthquakes. Key Points: We simulate multiple seismic cycles in a laboratory‐scale subduction zone with two asperitiesSlip‐deficit appears to be diagnostic of the location of highest slip but is poorly informative of the size of next eventDeciphering the spatially and temporally complex surface deformation history, ML predicts the timing and size of analog earthquakes [ABSTRACT FROM AUTHOR]

Taiwan is a young and seismically active mountain belt, where a series of strong earthquakes (M>7) have occurred over the past hundred years. Identifying historical earthquakes around Taiwan is a key to better constrain the geodynamic of this active region. Sedimentological and geochemical analyses of surface sediments from one station offshore east Taiwan revealed the presence of coarse-grained layers interpreted as turbidites. The age of these layers have been determined by 210Pb, 137Cs, and 241Am chronology. Dating of the three most recent turbidites provides ages of AD 2001±3, AD 1950±5, and AD 1928±10. The results show striking temporal correspondence of turbidite layers to large (M≥6.8) earthquakes recorded in the region since the 20th century. The chronologies of sediment layers lead us to believe that turbidites resulted from the 2003 Taitung earthquake (M 6.8), the 1951 Chengkong earthquake (M 7.1), and the 1935 Lutao earthquake (M 7.0), respectively. Such a good correlation between turbidites and high-magnitude (M≥6.8) historical and instrumental seismic events suggests that turbidite paleoseismology constitutes a valuable tool for earthquake assessment in the eastern Taiwan margin. Moreover, the modern reservoir radiocarbon age and the regional marine reservoir correction (ΔR) of the Kuroshio Current off Taiwan were estimated by comparing accelerator mass spectrometry (AMS) 14C ages with ages derived from corrected 210Pb profiles and historical accounts of identifiable seismic events. Such a determination is important to calibrate the 14C ages of marine materials for accurate comparison of marine and continental geological records. Our calculated mean ΔR value of 232±54 14C yr (n=2) is higher than its modern value of 86±40 14C yr. This high value can be explained by the presence of local upwelling cells and turbulence in the Kuroshio Current, north of Green Island. These upwelling cells bring 14C-depleted water to the surface, resulting in an increase of the modern ΔR value in this portion of the Kuroshio Current. [ABSTRACT FROM AUTHOR]

The Gagua Ridge, carried by the Philippine Sea Plate, is subducting obliquely beneath the southernmost Ryukyu Margin. Bathymetric swath-mapping, performed during the ACT survey (Active Collision in Taiwan), indicates that, due to the high obliquity of plate convergence, slip partitioning occurs within the Ryukyu accretionary wedge. A transcurrent fault, trending N95° E, is observed at the rear of the accretionary wedge. Evidence of right lateral motion along this shear zone, called the Yaeyama Fault, suggests that it accommodates part of the lateral component of the oblique convergence. The subduction of the ridge disturbs this tectonic setting and significantly deforms the Ryukyu Margin. The ridge strongly indents the front of the accretionary wedge and uplifts part of the forearc basin. In the frontal part of the margin, directly in the axis of the ridge, localized transpressive and transtensional structures can be observed superimposed on the uplifted accretionary complex. As shown by sandbox experiments, these N330° E to N30° E trending fractures result from the increasing compressional stress induced by the subduction of the ridge. Analog experiments have also shown that the reentrant associated with oblique ridge subduction exhibits a specific shape that can be correlated with the relative plate motion azimuth. These data, together with the study of the margin deformation, the uplift of the forearc basin and geodetic data, show that the subduction of the Gagua Ridge beneath the accretionary wedge occurs along an azimuth which is about 20° less oblique than the convergence between the PSP and the Ryukyu Arc. Taking into account the opening of the Okinawa backarc basin and partitioning at the rear of the accretionary wedge, convergence between the ridge and the overriding accretionary wedge appears to be close to N345° E and thus, occurs at a rate close to 9 cm yr−1. As a result, we estimate that a motion of 3.7 cm yr−1±0.7 cm should be absorbed along the transcurrent fault. Based on these assumptions, the plate tectonic reconstruction reveals that the subducted segment of the Gagua Ridge, associated with the observable margin deformations, could have started subducting less than 1 m.y. ago. [ABSTRACT FROM AUTHOR]