Complex Martinique Intermediate‐Depth Earthquake Reactivates Early Atlantic Break‐Up Structures

• Published in: Geophysical research letters 2024-06, Vol.51 (11), p.n/a
• Main Authors: Lindner, Mike, Rietbrock, Andreas, Bie, Lidong, Gao, Ya‐Jian, Goes, Saskia, Frietsch, Michael
• Format: Article
• Language: English
• Subjects: Deformation; Depth; Earthquakes; Fault lines; Faults; Fossils; Island arcs; Lithosphere; moment tensor; Ocean floor; Plate tectonics; Plates (tectonics); Proto‐Caribbean; ridge‐transform‐fault; Rupturing; Seismic activity; Seismic data; Seismic zones; Seismological data; source doublet; Structures; Subduction; Subduction (geology); subduction zone; Tensors; Waveforms
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108922

Earthquakes that rupture several faults occur frequently within the shallow lithosphere but are rarely observed for intermediate‐depth events (70–300 km). On 29 November 2007, the Mw7.4 Martinique earthquake struck the Lesser Antilles Island Arc near the deep end of the Wadati‐Benioff‐Zone. The sparse regional seismic network of 2007 previously hampered a detailed examination of this unusually complex event. Here, we combine seismic data from different studies with regional moment tensor inversion results and 3D full‐waveform modeling. We show that the earthquake is a doublet consisting of dip‐slip and strike‐slip motion along two oblique structures, both activated under extensional stress along the strike of the slab. Comparison with tectonic reconstructions suggests that the earthquake ruptured along a re‐activated ridge‐transform segment of the subducted Proto‐Caribbean spreading ridge. The unprecedented resolution of the source process highlights the influence of pre‐existing structures on localizing slab deformation also at intermediate‐depth. Plain Language Summary Some earthquakes in continents and near the ocean floor are known to break multiple, differently oriented, faults. Such compound earthquakes are rarely observed in subducted plates in the intermediate‐depth region between 70 and 300 km. Intermediate‐depth earthquake mechanics and stress state are possibly different from shallower earthquakes, and maybe they hinder complex events. On 29 November 2007, the Mw7.4 Martinique earthquake occurred at a depth of ∼150 km, near the deep end of the regional seismic zone below the Lesser Antilles Arc. The regional seismic network in 2007 was relatively sparse; it revealed the earthquake had a complex mechanism but did not previously allow for an in‐depth study. In this study, we combine different types of data and methods, including full waveform information, based on a recently derived 3D regional velocity model. Our analyses shows that the Martinique earthquake consisted of at least two distinct sub‐events on perpendicular faults in the subducted plate—a source doublet. By comparing the orientations of the doublet faults with plate tectonic reconstructions, we infer that this intermediate‐depth earthquake broke along a fossil plate‐boundary. This indicates that such structures remain structural weaknesses even after subduction. Key Points Moment tensor solutions, aftershock activity, back‐projection, and source‐time function suggest a complex ruptur