Structural analysis of fault populations along the oblique, ultra-slow spreading Knipovich Ridge, North Atlantic Ocean, 74°30′N-77°50′N

Curewitz, D.; Okino, Kyoko; Asada, Miho; Baranov, Boris; Гусев, Е. А.; Tamaki, Kensaku

doi:10.1016/j.jsg.2009.08.011

Cited by 19 publications

(29 citation statements)

References 63 publications

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“… Section ar_knip hosts a small swarm of low‐magnitude events where the detailed bathymetry of Okino et al (2002) shows a pair of elevated rift shoulders at both sides of the rift valley interpreted by Curewitz et al (2010) as symmetric chain of off‐axis highs. Comparable topographic highs are associated to the north with the Logachev Seamount (Fig.…”

Section: Description Of Resultsmentioning

confidence: 99%

Teleseismic earthquake swarms at ultraslow spreading ridges: indicator for dyke intrusions?

Schlindwein¹

2012

Geophysical Journal International

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SUMMARY Earthquakes at mid‐ocean ridges reflect the active magmatic and tectonic processes that form new oceanic crust. Studies of large earthquakes observed on land and smaller earthquakes observed locally or regionally by ocean bottom seismometers or autonomous underwater hydrophones have greatly contributed to our understanding of the structure and active spreading processes at the mid‐ocean ridges of the Atlantic and Pacific Ocean opening with velocities in excess of 25 mm yr–1. At spreading rates below 20 mm yr–1 full rate, the appearance and the accretion processes of mid‐ocean ridges undergo fundamental changes as the melt supply is drastically reduced. The active spreading processes at these so‐called ultraslow spreading ridges are still poorly known, as the main representatives, the Arctic Ridge System and the Southwest Indian Ridge, are poorly accessible and neither autonomous underwater hydrophone nor ocean bottom seismometer records of local seismicity are available. In an attempt to compare on a large scale the accretion style of ultraslow spreading ridge sections, I analyse the teleseismically recorded seismicity in 11 sections of the Arctic Ridge System and the Southwest Indian Ridge spanning altogether 7200 km. Epicentres located within 30–35 km of the rift axis were extracted from the catalogue of the International Seismological Centre for a time period of 35 yr. On the basis of a single‐link cluster analysis, I identified 27 swarms with eight or more events. These swarms occur almost exclusively at centres of focussed magmatism suggesting that the swarms are probably initiated by magmatism. Normal faults along several tens of kilometres surrounding the volcanic centres react in large earthquakes (M > 5) to dyke emplacement. The routine generation of large earthquakes in the cold, brittle lithosphere of ultraslow spreading ridges makes the teleseismic record a valuable means to study ultraslow accretion processes and to provide a global framework for the interpretation of the limited local and regional seismicity studies.

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Section: Description Of Resultsmentioning

confidence: 99%

Teleseismic earthquake swarms at ultraslow spreading ridges: indicator for dyke intrusions?

Schlindwein¹

2012

Geophysical Journal International

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“…It has been suggested that under the oblique‐spreading environment, the axial rift valley acts as a weakness zone to localize the brittle failures, whereas the trend of intrarift fabrics are mainly controlled by the orthogonal extension or transtension [ Sauter et al , ; Cannat et al , ; Dick et al , ; Tuckwell et al , ]. Side‐scan sonar images at other oblique‐spreading ultraslow ridge segments have revealed the systematic variation from magmatic segment centers to segment ends, where faults become more oblique, shorter, and denser [ Sauter et al , ; Curewitz et al , ]. Our results demonstrate that the orthogonal extension and dyke injection are favored throughout the lithosphere at the magmatic segment center, possibly due to the small thickness of the lithosphere and the magma pressure from the asthenosphere.…”

Section: Discussionmentioning

confidence: 99%

Seismic structure and magmatic construction of crust at the ultraslow‐spreading Southwest Indian Ridge at 50°28'E

et al. 2017

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We present a three‐dimensional crustal structure of a magmatically robust segment of the ultraslow‐spreading Southwest Indian Ridge at 50°28'E based on tomographic inversions of an ocean bottom seismometer data set. Our results show an upper crustal low‐velocity band in the axial zone, which is attributed to increased porosities due to active extensions, leading to anisotropy in the upper crust with a fast direction subperpendicular to the spreading direction. In the lower crust, the results reveal a round‐shaped low‐velocity anomaly at the segment center, indicative of high temperatures and/or a small amount of melt, suggestive of the presence of an axial magma chamber. At the midcrustal depth, an along‐axis asymmetry is observed with respect to the segment center. While a small low‐velocity anomaly indicates lateral magma redistribution toward the western segment end, the deep‐penetrating low velocities and high velocity gradients toward the eastern end suggest that the crust is colder and contains a thicker fractured layer. This asymmetry occurs very close to the axial magma chamber (<5 km) and seems to be related to the fact that the oblique‐spreading domain at the eastern end offsets the ridge axis by a larger distance than that at the western end. We suggest that an along‐axis deep‐penetrating hydrothermal circulation develops on the east side of the axial magma chamber, in response to the rapid change from orthogonal‐ to oblique‐spreading domains and cools the crust.

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“…The 3000 m contour line is plotted in red. The contour interval is 100 m. Spreading directions according to Curewitz et al [2009]. since this would weaken mantle peridotites sufficiently to exclude brittle failure [Escartin et al, 1997].…”

Section: Discussionmentioning

confidence: 99%

Crustal thickness and earthquake distribution south of the Logachev Seamount, Knipovich Ridge

Jokat

Kollofrath

Geissler

et al. 2012

Geophysical Research Letters

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During RV Polarstern cruise ARK‐XXIV/3 (2009), a geophysical study along the ultraslow spreading Knipovich Ridge was conducted. The survey, located in the rift valley south of the Logachev Seamount (∼76°36′N), provides a crustal thickness of ∼4.5 km in the amagmatic parts and 5.7 km underneath the seamount itself. The velocity‐depth function indicates the presence of a thick oceanic layer 2 (4.5 km), but no indication for a thick oceanic layer 3. The only exception is the area underneath the Logachev Seamount, where velocities higher than 6 km/s are detected. This indicates a stronger and focussed melt supply underneath the seamount. Local seismicity was analysed for two days. In total, 191 quakes were identified in the vicinity of the rift valley with magnitudes up to ML = 2.6. At least 48 of them are located in the upper mantle (up to 18 km below sea level), supporting models predicting a cold mantle or conductive cooling underneath ultraslow ridges to explain the reduced melt supply.

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Structural analysis of fault populations along the oblique, ultra-slow spreading Knipovich Ridge, North Atlantic Ocean, 74°30′N-77°50′N

Cited by 19 publications

References 63 publications

Teleseismic earthquake swarms at ultraslow spreading ridges: indicator for dyke intrusions?

Teleseismic earthquake swarms at ultraslow spreading ridges: indicator for dyke intrusions?

Seismic structure and magmatic construction of crust at the ultraslow‐spreading Southwest Indian Ridge at 50°28'E

Crustal thickness and earthquake distribution south of the Logachev Seamount, Knipovich Ridge

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