Microearthquake activity at the Oblique Supersegment of the Southwest Indian Ridge in the period 2012-12 until 2013-11

DOI

While nascent oceanic lithosphere at slow to fast spreading mid-ocean ridges (MOR) is relatively well studied, much less is known about the lithospheric structure and properties at ultraslow MORs. Here we present microearthquake data from a 1 year ocean bottom seismometer deployment at the amagmatic, oblique supersegment of the ultraslow spreading Southwest Indian Ridge. A refraction seismic experiment was performed to constrain upper lithosphere P-velocities and results were used to construct a 1D velocity model for earthquake location. Earthquake foci were located individually and subsequently relocated relative to each other to sharpen the image of seismically active structures. Frequent earthquake activity extends to 31 km beneath the seafloor, indicating an exceptionally thick brittle lithosphere and an undulating brittle-ductile transition that implies significant variations in the along-axis thermal structure of the lithosphere. We observe a strong relation between petrology, microseismicity distribution, and topography along the ridge axis: Peridotite-dominated areas associate with deepest hypocenters, vast volumes of lithosphere that deforms aseismically as a consequence of alteration, and the deepest axial rift valley. Areas of basalt exposure correspond to shallower hypocenters, shallower and more rugged axial seafloor. Focal mechanisms deviate from pure extension and are spatially variable. Earthquakes form an undulating band of background seismicity and do not delineate discrete detachment faults as common on slow spreading ridges. Instead, the seismicity band sharply terminates to the south, immediately beneath the rift boundary. Considering the deep alteration, large steep boundary faults might be present but are entirely aseismic.

Supplement to: Schmid, Florian; Schlindwein, Vera (submitted): Lithospheric strength, thermal structure, diffusive geochemical fluxes and microbial activity in the ultraslow spreading Southwest Indian Ridge axial valley. Geochemistry, Geophysics, Geosystems

Identifier
DOI https://doi.org/10.1594/PANGAEA.881384
Related Identifier References https://doi.org/10.1038/nature18277
Related Identifier IsDocumentedBy https://doi.org/10.1594/PANGAEA.881385
Metadata Access https://ws.pangaea.de/oai/provider?verb=GetRecord&metadataPrefix=datacite4&identifier=oai:pangaea.de:doi:10.1594/PANGAEA.881384
Provenance
Creator Schmid, Florian ORCID logo; Schlindwein, Vera ORCID logo
Publisher PANGAEA
Publication Year 2017
Rights Creative Commons Attribution 3.0 Unported; https://creativecommons.org/licenses/by/3.0/
OpenAccess true
Representation
Resource Type Supplementary Dataset; Dataset
Format text/tab-separated-values
Size 19476 data points
Discipline Earth System Research
Spatial Coverage (10.785W, -52.943S, 17.140E, -51.228N); South Atlantic Ocean
Temporal Coverage Begin 2012-12-07T01:06:05Z
Temporal Coverage End 2013-11-20T11:51:29Z