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Signature estimation is critical for source evaluation and data processing. Far-field measurement is an accurate way to deterministically finalize the process and more importantly to clarify the source directivity. Based on the position-fixed mode, a seismic survey is carried out in India Ocean in 2021 with a deep-towed Janus-Helmholtz (JH) transducer as the source. This work shows a full view of acquiring, processing, and analyzing the far-field source signature. According to the source-receiver reciprocity theorem, an incidence angle of 7.4°–87.8° is covered in this survey. In order to overcome the positioning uncertainty of the ultrashort baseline mode, a novel joint ray-tracing inversion approach is presented on the basis of the conductivity-temperature-depth (CTD)-derived sound velocity model. On the data processing side, a customized workflow is established to attenuate the complex sea-floor reflections. It is realized based on sparse f–k transformation and adaptive subtraction and is validated effective from both the shot gather and spectrum panel. Analysis indicates that the signature of the transducer is jointly affected by the input assignment and the system response. It is potential to tune the two factors to optimize the signature, e.g., widening its bandwidth. Moreover, strong directivity is observed in terms of waveform consistency, amplitude decay, and energy distribution, which challenges the point-source propagation theory. Missing of the directivity information may cause severe imaging issues as illustrated by the comparison between global and directional deconvolution. This work could be a good guideline for future signature estimation and so-based data processing and analysis.

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. 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. 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 Our tectonomagmatic models provide a mechanical explanation for the sequentially active detachment fault system at the Longqi segment on the ultraslow spreading ridges Lithospheric structure at spreading centers plays a key role in the lifecycle of oceanic detachment faults