TY  - JOUR
A1  - Hannemann, Katrin
A1  - Krüger, Frank
A1  - Dahm, Torsten
A1  - Lange, Dietrich
T1  - Structure of the oceanic lithosphere and upper mantle north of the Gloria Fault in the eastern mid-Atlantic by receiver function analysis
JF  - Journal of geophysical research : Solid earth
N2  - Receiver functions (RF) have been used for several decades to study structures beneath seismic stations. Although most available stations are deployed on shore, the number of ocean bottom station (OBS) experiments has increased in recent years. Almost all OBSs have to deal with higher noise levels and a limited deployment time (approximate to 1year), resulting in a small number of usable records of teleseismic earthquakes. Here we use OBSs deployed as midaperture array in the deep ocean (4.5-5.5km water depth) of the eastern mid-Atlantic. We use evaluation criteria for OBS data and beamforming to enhance the quality of the RFs. Although some stations show reverberations caused by sedimentary cover, we are able to identify the Moho signal, indicating a normal thickness (5-8km) of oceanic crust. Observations at single stations with thin sediments (300-400m) indicate that a probable sharp lithosphere-asthenosphere boundary (LAB) might exist at a depth of approximate to 70-80km which is in line with LAB depth estimates for similar lithospheric ages in the Pacific. The mantle discontinuities at approximate to 410km and approximate to 660km are clearly identifiable. Their delay times are in agreement with PREM. Overall the usage of beam-formed earthquake recordings for OBS RF analysis is an excellent way to increase the signal quality and the number of usable events.
KW  - receiver function
KW  - oceanic lithosphere and mantle
KW  - ocean bottom seismology
Y1  - 2017
U6  - https://doi.org/10.1002/2016JB013582
SN  - 2169-9313
SN  - 2169-9356
VL  - 122
SP  - 7927
EP  - 7950
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Vinnik, Lev
A1  - Silveira, Graca
A1  - Kiselev, Sergei
A1  - Farra, Veronique
A1  - Weber, Michael H.
A1  - Stutzmann, Eleonore
T1  - Cape verde hotspot from the upper crust to the top of the lower mantle
JF  - Earth & planetary science letters
N2  - We investigate the crust, upper mantle and mantle transition zone of the Cape Verde hotspot by using seismic P and S receiver functions from several tens of local seismograph stations. We find a strong discontinuity at a depth of similar to 10 km underlain by a similar to 15-km thick layer with a high (similar to 1.9) Vp/Vs velocity ratio. We interpret this discontinuity and the underlying layer as the fossil Moho, inherited from the pre-hotspot era, and the plume-related magmatic underplate. Our uppermost-mantle models are very different from those previously obtained for this region: our S velocity is much lower and there are no indications of low densities. Contrary to previously published arguments for the standard transition zone thickness our data indicate that this thickness under the Cape Verde islands is up to similar to 30 km less than in the ambient mantle. This reduction is a combined effect of a depression of the 410-km discontinuity and an uplift of the 660-km discontinuity. The uplift is in contrast to laboratory data and some seismic data on a negligible dependence of depth of the 660-km discontinuity on temperature in hotspots. A large negative pressure-temperature slope which is suggested by our data implies that the 660-km discontinuity may resist passage of the plume.
 Our data reveal beneath the islands a reduction of S velocity of a few percent between 470-km and 510-km depths. The low velocity layer in the upper transition zone under the Cape Verde archipelago is very similar to that previously found under the Azores and a few other hotspots. In the literature there are reports on a regional 520-km discontinuity, the impedance of which is too large to be explained by the known phase transitions. Our observations suggest that the 520-km discontinuity may present the base of the low-velocity layer in the transition zone.
KW  - hotspot
KW  - plume
KW  - crust
KW  - upper mantle
KW  - mantle transition zone
KW  - receiver function
Y1  - 2012
U6  - https://doi.org/10.1016/j.epsl.2011.12.017
SN  - 0012-821X
VL  - 319
IS  - 4
SP  - 259
EP  - 268
PB  - Elsevier
CY  - Amsterdam
ER  -