Seismicity of mid-oceanic ridges and its geodynamic implications: a review

Rundquist, D. V.; Sobolev, P. O.

doi:10.1016/s0012-8252(01)00086-1

Cited by 51 publications

(36 citation statements)

References 83 publications

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“…The general seismicity of oceanic ridges is well understood (e.g. Rundquist & Sobolev 2002), with earthquakes generally limited to depths of ≤10 km below the seabed, in agreement with the depth of the 600 °C isotherm (M c Kenzie et al 2005). Events along the active spreading ridges of Aden and the Red Sea are confined to centroid depths of ≤11 km below sea or land surface (Fig.…”

Section: Africa–arabia Extension: Red Sea and Gulf Of Adenmentioning

confidence: 71%

Earthquake distribution patterns in Africa: their relationship to variations in lithospheric and geological structure, and their rheological implications

Craig

Jackson

Priestley

et al. 2011

Geophysical Journal International

201

221

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SUMMARY We use teleseismic waveform inversion, along with depth phase analysis, to constrain the centroid depths and source parameters of large African earthquakes. The majority of seismic activity is concentrated along the East African Rift System, with additional active regions along stretches of the continental margins in north and east Africa, and in the Congo Basin. We examine variations in the seismogenic thickness across Africa, based on a total of 227 well‐determined earthquake depths, 112 of which are new to this study. Seismogenic thickness varies in correspondence with lithospheric thickness, as determined from surface wave tomography, with regions of thick lithosphere being associated with seismogenic thicknesses of up to 40 km. In regions of thin lithosphere, the seismogenic thickness is typically limited to ≤20 km. Larger seismogenic thicknesses also correlate with regions that have dominant tectonothermal ages of ≥1500 Ma, where the East African Rift passes around the Archean cratons of Africa, through the older Proterozoic mobile belts. These correlations are likely to be related to the production, affected by method and age of basement formation, and preservation, affected by lithospheric thickness, of a strong, anhydrous lower crust. The Congo Basin contains the only compressional earthquakes in the continental interior. Simple modelling of the forces induced by convective support of the African plate, based on long‐wavelength free‐air gravity anomalies, indicates that epeirogenic effects are sufficient to account for the localization and occurrence of both extensional and compressional deformation in Africa. Seismicity along the margins of Africa reflects a mixture between oceanic and continental seismogenic characteristics, with earthquakes in places extending to 40 km depth.

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Section: Africa–arabia Extension: Red Sea and Gulf Of Adenmentioning

confidence: 71%

Earthquake distribution patterns in Africa: their relationship to variations in lithospheric and geological structure, and their rheological implications

Craig

Jackson

Priestley

et al. 2011

Geophysical Journal International

201

221

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“…To locate the plate boundary, i.e., the ridge segments and transform faults, we perform an integrated analysis of the seismological and geophysical data within each province. The analysis takes into account that (1) the largest earthquakes occur at transform faults [ Rundquist and Sobolev , 2002] while swarms of smaller earthquakes commonly reflect extensional tectonics [ Bergman and Solomon , 1990], (2) the axial bathymetry reflects the rift valley and characteristic transform features such as transform valleys, nodal basins, and high inside corners [ Fox and Gallo , 1984], (3) free‐air gravity anomalies which originate mainly from the seafloor and basement topographies, may be considered as low‐pass filtered bathymetry [e.g., Smith and Sandwell , 1994], thus enhancing regional features, and (4) the pattern of near‐axis magnetic lineations is offset across fracture zones (FZ). In addition, we have constructed synthetic flowlines from the Norwegian–Greenland Sea rotation poles of Talwani and Eldholm [1977] to examine the regional consistency of the inferred transform trends and whether they may extend as fracture zones into the adjacent basins.…”

Section: Arctic Mid‐oceanic Ridgementioning

confidence: 99%

The Arctic plate boundary

2003

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[1] Earthquakes provide information on the regional segmentation and seismotectonics of the poorly known boundary between the Eurasian and the North American plates from the Knipovich Ridge to the Laptev Sea continental margin. To this end, we have sorted earthquake epicenter locations and focal mechanism solutions from global and regional catalogs, assessed location errors and network detectabilities, and compiled a well-constrained Arctic Catalog of events north of 72°N for the period 1955-1999. The seismological data are integrated with bathymetry and potential field data to locate ridge and transform segments along the Arctic mid-oceanic ridge (MOR), and we suggest that the plate boundary is divided into four regional provinces. The Spitsbergen Transform System comprises a series of short ridge and transform segments. The seismicity is constrained to the plate boundary in the south but is diffuse in the north. Gakkel Ridge has clustered and focused seismicity and relatively elongated ridge segments cut by small-offset transforms. A first-order change in axis trend at 60°E divides the ridge into two areas of different morphology and geophysical character. The West Gakkel Ridge has an accentuated relief and highamplitude magnetic anomalies, whereas the East Gakkel Ridge has a smoother relief and lower magnetic amplitudes. At the Laptev Sea continental slope, the seismicity indicates that the change from ultraslow seafloor spreading to active continental rifting occurs over a less than 60 km wide continent-ocean transition (COT) with a 150-200 km long sheared margin segment.

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“…Cowie et al [1993] later argued that seismic slip had to represent an insignificant fraction (<1%) of the time-averaged fault slip rate at the fast-spreading East Pacific Rise. Subsequent studies documented an exponential decrease in seismic moment release rates, and thus seismically accommodated strain, between slow and fast spreading centers [Sobolev and Rundquist, 1999;Rundquist and Sobolev, 2002;Bird et al, 2002;Frohlich and Wetzel, 2007]. This article is protected by copyright.…”

Section: Introductionmentioning

confidence: 99%

“…A commonly accepted interpretation for this trend is that it reflects the warmer thermal structure of faster-spreading ridges, which potentially reduces the area of the fault where seismic slip can occur [Cowie et al, 1993;Rundquist and Sobolev, 2002]. In this scenario, the limited contribution of coseismic displacements to long-term fault slip reflects the limited spatial extent of seismic ruptures relative to the total fault surface.…”

Section: Introductionmentioning

confidence: 99%

Dependence of seismic coupling on normal fault style along the Northern Mid‐Atlantic Ridge

Olive

Escartı́n

2016

Geochem Geophys Geosyst

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Key points• Greater seismic moment release rates at detachment-bearing sections of the Mid-Atlantic Ridge compared to abyssal hill-bearing sections.• Coupled seismic thickness likely greatest (~2 km) at individual detachment faults of finite along-axis extent, and averages ~500 m elsewhere.• Rate and state friction theory attributes differences in seismic coupling to the thermomechanical state and lithology of oceanic normal faults. AbstractWhile normal faults are essential in shaping the seafloor formed at slow-spreading mid-ocean ridges, information on their behavior on short (seismic cycle) time scales is limited. Here we combine catalogs of hydro-acoustically and teleseismically recorded earthquakes to characterize the state of seismic coupling along the Northern Mid-Atlantic Ridge (MAR) between 12 and 35ºN. Along this portion of the MAR axis, tectonic extension is either taken up by steep conjugate faults that outline well-defined ridgeparallel abyssal hills, or dominantly by a large-offset detachment fault on one side of the axis.We investigate variations in seismicity and seismic moment release rates across thirty ridge sections that can be clearly characterized either as abyssal hill or detachment bearing. We find that detachment-bearing sections are associated with significantly greater seismicity and moment release rates than abyssal hill bearing sections, but show variability that may reflect the along-axis extent of individual detachment faults. Overall, the measured seismic moment release rates fail to account for the long-term fault slip rates. This apparent seismic deficit could indicate a mixed-mode of fault slip where earthquakes only account for ~10-30% of offset build-up at abyssal hill faults, while the rest is accommodated by some form of transient aseismic creep. We find this seismic coupling fraction to be significantly greater (~40-60%) at individual detachment systems, which is somewhat at odds with the common inference that detachment faults can sustain long-lived localized strain because they are weak. We therefore propose alternative interpretations for seismic coupling based on dynamic friction theory.

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Seismicity of mid-oceanic ridges and its geodynamic implications: a review

Cited by 51 publications

References 83 publications

Earthquake distribution patterns in Africa: their relationship to variations in lithospheric and geological structure, and their rheological implications

Earthquake distribution patterns in Africa: their relationship to variations in lithospheric and geological structure, and their rheological implications

The Arctic plate boundary

Dependence of seismic coupling on normal fault style along the Northern Mid‐Atlantic Ridge

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