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Schmid, Florian; Schlindwein, Vera (2017): Microearthquake activity at the Oblique Supersegment of the Southwest Indian Ridge in the period 2012-12 until 2013-11. PANGAEA, https://doi.org/10.1594/PANGAEA.881384, Supplement to: Schmid, F; Schlindwein, V (2016): Microearthquake activity, lithospheric structure, and deformation modes at an amagmatic ultraslow spreading Southwest Indian Ridge segment. Geochemistry, Geophysics, Geosystems, 17(7), 2905-2921, https://doi.org/10.1002/2016GC006271

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Abstract:
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.
Related to:
Schlindwein, Vera; Schmid, Florian (2016): Mid-ocean-ridge seismicity reveals extreme types of ocean lithosphere. Nature, 535(7611), 276-279, https://doi.org/10.1038/nature18277
Further details:
Schmid, Florian; Schlindwein, Vera (2017): Positions of the ocean bottom seismometers that recorded the earthquakes. PANGAEA, https://doi.org/10.1594/PANGAEA.881385
Project(s):
Coverage:
Median Latitude: -52.338573 * Median Longitude: 13.487258 * South-bound Latitude: -52.943000 * West-bound Longitude: 10.785000 * North-bound Latitude: -51.228000 * East-bound Longitude: 17.140000
Date/Time Start: 2012-12-07T01:06:05 * Date/Time End: 2013-11-20T11:51:29
Event(s):
SWIR (Southwest Indian Ridge) * Latitude Start: -52.800000 * Longitude Start: 11.300000 * Latitude End: -52.200000 * Longitude End: 15.600000 * Location: South Atlantic Ocean
Parameter(s):
#NameShort NameUnitPrincipal InvestigatorMethod/DeviceComment
1DATE/TIMEDate/TimeSchmid, FlorianGeocode
2ErrorErrorSchmid, FlorianOrigin time error in seconds
3LATITUDELatitudeSchmid, FlorianGeocode
4LONGITUDELongitudeSchmid, FlorianGeocode
5Azimuth of major half-axis of the location error ellipseAzimuth majordegSchmid, Florianclockwise from north
6Length of the major half-axis of the error ellipseLength majorkmSchmid, Florian
7Length of the minor half-axis of the error ellipseLength minorkmSchmid, Florian
8Hypocentre depthHCDkmSchmid, Florian
9Hypocentre depth, errorHCD errkmSchmid, Florian
10Local magnitudeLocal magSchmid, Florian
11Root-mean-square residual of the solutionminRMSsSchmid, Florian
12Number of defining phasesNumber defining phases#Schmid, Florian
13Number of observationsNOBS#Schmid, FlorianNumber of recording stations
Size:
19476 data points

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