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We discuss the tectonic structure, seismic stratigraphy and evolution of the NW Sulu Sea using reprocessed 2D reflection profiles. The NW Sulu Sea is located between the Palawan continental shelf and the Cagayan Ridge and represents the northern part of the Sulu Sea, a marginal sea resulting from Paleogene extension and subsequent Neogene contraction due to convergence between the Palawan and the Philippine blocks. The basin consists of six seismo‐stratigraphic units overlying crystalline basement. Syn‐orogenic depocenters contain calibrated Middle Miocene to, possibly, Lower Miocene units, while rift‐related depocenters consist of uncalibrated but tentatively dated Paleogene to Lower Miocene units. Thickness and depth maps of the main units and bounding horizons differentiate the Piedra‐Blanca and the Rasa domains, separated by the NW‐Sulu‐Break major tectonic structure. Fault‐bounded rift‐related depocenters are strongly segmented. We interpret that NW‐SE and NE‐SW trending zones accommodate shape and trend variations of these depocenters. We suggest that these zones may link rift segments, recording different extensional deformation. Miocene thrusting and folding in the Piedra‐Blanca Domain and mudflow with associated gravitational structures in the Rasa Domain influenced the deposition of syn‐orogenic units. Rift structures inherited from rift segmentation may have conditioned the style and distribution of contractional deformation during the subsequent incipient reactivation during contraction. In the context of SE Asia, our results support that the timing of rifting of the NW Sulu Sea overlaps with the opening of the South China Sea and the North Palawan margin, which may indicate a common geodynamic driving force triggering extension. Plain Language Summary: The SE Asia region includes several basins partially floored by oceanic crust, frequently containing or bounded by volcanic island arcs. These basins are known marginal seas and, although it is critical to decipher the geodynamic evolution of the entire region, the structure and tectonic history of most of these marginal seas are still insufficiently known. The Sulu marginal sea lies between the Sulu Archipelago and the Palawan, Mindanao, Negros and Panay islands. The Cagayan Ridge separates the NW and SE Sulu seas, which show a contrasting seafloor morphology, resulting from Paleogene extension and subsequent Neogene contraction. In this work, we study the structure and tectonic evolution of the NW Sulu Sea based on the re‐processing and interpretation of seismic reflection profiles acquired in 1982 and 1987. We analyzed and calibrated the seismo‐stratigraphy of the sediment infill, determined the main tectonic and gravitational structures and the geometry and spatial distribution of depocenters. Our results show for the first time the basin‐wide overall structure and constrain tectonic models, describing the opening and, particularly, the contractional deformation of the NW Sulu Sea. This provides further information to understand the formation of the Sulu Sea and the evolution of convergent systems in SE Asia. Key Points: A multi‐stage tectonic evolution shaped the Piedra‐Blanca and Rasa structural domains separated by the gentle NW‐Sulu‐Break structureNW‐SE and NE‐SW trending accommodation zones define the geometry and location of the rift‐related oldest basin depocentersThrusts and associated folds deformed the Piedra‐Blanca and mudflows affected the Rasa domain during the contractional basin reactivation [ABSTRACT FROM AUTHOR]

An analysis of 2 decades (2003–2022) of seismicity recorded by the Spanish and Portuguese seismic networks along the West Iberian passive margin has resulted in a better understanding of the distribution of moderate seismic activity in this intraplate submarine area. The study provides a precise trend of specific alignments inferred from the density maps of seismicity, giving an accurate depiction of event distribution along two wide stripes that extend for 700 km through the ocean floor in the WNW–ESE direction. These bands are parallel to the Africa–Eurasia plate boundary but are distinctly separated from its related seismicity by approximately 300 and 700 km, respectively. This is a sufficient distance to be considered intraplate activity. When trying to relate this seismicity to structural and geophysical features, a conclusive picture does not emerge. The earthquakes occur indiscriminately across thinned continental, hyperextended, and exhumed mantle rift domains. They fade out in proximity to undisputed oceanic crust, but some events extend beyond. The hypocentral depths signal a considerable number of events nucleating in the upper mantle. The focal mechanisms, although scarce, are predominantly strike-slip. Considering these observations, hypotheses ranging from subduction initiation and development of strained corridors to local structures of the margin are discussed in order to explain this relatively anomalous seismicity. However, some of them lack convincing arguments, while others are too vague. None of them are flawless, suggesting that several factors may be at play. Despite being one of the most probed passive margins in the world, the present geodynamic status of the West Iberian Margin manifested in its modern seismicity remains unknown. Interpreting these data within a global tectonic plate framework, together with the potential addition of seafloor seismometers, may provide the key to understanding this activity along one of the most archetypical margins of the Atlantic Ocean. [ABSTRACT FROM AUTHOR]

An analysis of two decades (2003–2022) of seismicity recorded by the Spanish and Portuguese seismic networks along the West Iberian passive margin has resulted in a better understanding of the distribution of moderate seismic activity in this intraplate submarine area. The study provides a precise trend of specific alignments inferred from the density maps of seismicity, giving an accurate depiction of event distribution along two wide stripes that extend 700 km long through the ocean floor in a WNW-ESE direction. These bands are parallel to the Africa-Eurasia plate boundary but are distinctly separated from its related seismicity by approximately 300 km and 700 km, respectively. This is a sufficient distance to be considered as intraplate activity. When trying to relate this seismicity to structural and geophysical features, a conclusive picture doesn't emerge. The earthquakes occur indiscriminately across thinned continental, hyperextended, and exhumed mantle rift domains. They fade out in the proximity of undisputed oceanic crust, but some events extend beyond. The hypocentral depths signal a considerable amount of events nucleating in the upper mantle. The focal mechanisms, although scarce, are predominantly strike-slip. Considering these observations, hypothesis ranging from subduction initiation, development of strained corridors or local structures of the margin, have been discussed in order to explain this relatively anomalous seismicity. However, some of them do not portray convincing arguments, while others are too unspecific. None of them are flawless, suggesting that several factors may be at play. Despite being one of the most probed passive margins in the world, the present geodynamical status of the West Iberian Margin manifested in its modern seismicity remains unknown. Interpreting this data within a global tectonic plate framework, together with the potential addition of seafloor seismometers, may provide the key to understanding this activity along one of the most archetypical margins of the Atlantic Ocean. [ABSTRACT FROM AUTHOR]