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Density is an important parameter for both geological research and geophysical exploration. However, for model-driven seismic inversion methods, high-fidelity density inversion is challenging due to seismic wave traveltime insensitivity to density and crosstalk that density has with velocity. To circumvent the challenge of density inversion, some inversion methods treat density as a constant value or derive density from velocity through empirical equation. On the other hand, deep learning approaches are completely driven by data and have strong target-oriented characteristics, offering a new way to solve multiparameter coupling problems. Nevertheless, the accuracy of the inversion results of data-driven algorithms is directly related to the amount and diversity of the training data, and thus, they lack the universality of model-driven algorithms. To achieve accurate density inversion, we propose a simultaneous inversion algorithm for velocity and density that combines the advantages of data- and model- driven approaches: A neural network model (U-T), combining the U-net and Transformer architectures, is proposed to construct non-linear mappings between seismic data as inputs and the velocity and density as predictions. Next, the model-driven inversion algorithm uses the U-T prediction as the initial model to obtain the final accurate solution. In the model-driven module, envelope-based sparse constrained deconvolution is used to obtain full-band seismic data, while a variable dominant frequency full waveform inversion algorithm is used to perform multiscale inversion, ultimately leading to accurate inversion results of velocity and density. The performance of the algorithm on the Sigsbee2A and Marmousi models demonstrates its effectiveness. [ABSTRACT FROM AUTHOR]

Oceanic detachment faulting, a major mode of seafloor accretion at slow and ultraslow spreading ridges, is thought to occur during magma‐poor phases and be abandoned when magmatism increases. In this framework, detachment faulting is the result of temporal variations in magma flux, which is inconsistent with recent geophysical observations at the Longqi segment on the Southwest Indian Ridge (49°42′E). In this paper, we focus on this sequentially active detachment faulting system that includes an old, inactive detachment fault and a younger, active detachment fault. We investigate the mechanisms controlling the temporal evolution of this tectonomagmatic system by using 2D mid‐ocean ridge spreading models that simulate faulting and magma intrusion into a visco‐elasto‐plastic continuum. Our models show that temporal variations in magma flux alone are insufficient to match the inferred temporal evolution of the sequentially active detachment system. Rather we find that sequentially active detachment faulting spontaneously occurs at the Longqi segment as a function of lithospheric thickness. This finding is in agreement with an analytical model, which shows that a thicker axial lithosphere results in a smaller fault heave and that a flatter angle in lithosphere thickening away from the accretion axis stabilizes the active fault. A thicker axial lithosphere and its flatter off‐axis angle combined have the potential to modulate sequentially active detachment faulting at the Longqi segment. Our results thus suggest that temporal changes of magmatism are not necessary for the development and abandonment of detachment faults at ultraslow spreading ridges. Plain Language Summary: The oceanic lithosphere is frequently generated through slip on long‐lived faults called oceanic detachment faults, which exhume lower crustal and upper mantle materials on the seabed and form dome‐shaped features. Yet, oceanic detachment faulting is a sequentially active process and previous studies have focused on temporal variations in magma flux as the primary cause. Magma flux refers to the rate at which the continuous flow of magma moves from melted mantle at depth toward the ridge axis through volcanic vents or fissures. In the presented manuscript we show that this standard model does not work for the ultraslow spreading Southwest Indian Ridge (49°42′E). Here, we present geological and geophysical evidence that the magma flux had remained stable during the two most recent phases of detachment faulting. We investigate the mechanisms controlling the life cycle of the detachment fault by using a 2D geodynamics model. We compare model results with observations and propose that sequentially active detachment faulting at the Longqi segment is a function of lithospheric structure rather than variations in magma flux. These findings show that temporal changes of magmatism are not required for sequentially active detachment faulting to occur. Key Points: Our tectonomagmatic models provide a mechanical explanation for the sequentially active detachment fault system at the Longqi segment on the ultraslow spreading ridgesLithospheric structure at spreading centers plays a key role in the lifecycle of oceanic detachment faults [ABSTRACT FROM AUTHOR]

Unwanted interference noise often causes problems during seismic reflection data acquisition and processing. In this paper we present two novel data‐regrouping methods that enable improved shot‐to‐shot coherent interference noise attenuation in marine seismic data. The two approaches are based on line mixing and/or shot skipping: (1) for a 3‐D marine seismic reflection data acquisition which is typically carried out by shooting closely spaced parallel lines, we propose to mix the shot gathers from two adjacent sail lines to break up shot‐to‐shot coherent noise. This approach takes advantage of the fact that adjacent sail lines are usually acquired with a significant time interval, resulting in different types of noise; (2) for a 2‐D/3‐D acquisition, we propose an algorithm to skip and reorder the original shots to decrease the continuity of the shot‐to‐shot coherent noise. This approach could also supply more aperture data for the first or last shot from both sides, which is beneficial for the coherent noise removal at the edge area. After regrouping the original data, the coherent noise can then be further randomized or isolated by sorting and transforming to other domains, typically the common p‐shot domain where a random noise attenuation tool could be applied to identify and attenuate such noise. Field data examples confirm the effectiveness of the methods. Key Points: This paper illustrates the generation and distribution characteristics of coherent noise, especially the rig noise and seismic interferenceThis paper presents two novel approaches to break up the consistency of shot‐to‐shot coherent noise resulting in very good denoised resultStatistics show that data‐regrouping methods combined with cross‐party vessel cooperation significantly reduced the time‐sharing cost [ABSTRACT FROM AUTHOR]

In this paper, we describe the results of a first pilot experiment of passive seismic monitoring near the active Longqi hydrothermal vent at the Southwest Indian Ridge during Chinese cruise DY115-30. During 102-day experiment, we recorded over 2,000 seismic events on a single ocean bottom seismometer with hydrophone close to the hydrothermal field. We classified these events into the following three classes based on their time–frequency characteristics: (1) volcano tectonic microearthquakes (VTMs); (2) regional earthquakes; (3) short-duration events (SDEs). We preliminarily located the 1,277 VTMs using a single-station location method. Our results revealed hypocenters primarily beneath the axial valley ridge which is about 10 km away from hydrothermal vent and extending to the upper mantle at a depth of 15 km. Two discrete swarms of VTMs occurred during our survey period. The SDEs show a complex frequency characteristics ascribed to clusters of monochromatic waves around different frequencies. This suggests that SDEs result from combination of harmonic waves resonating in fluid-filled pipes and cracks. [ABSTRACT FROM AUTHOR]