Caribbean slab dynamics beneath northwest South America from SKS and Local S splitting

2021 ◽  
Author(s):  
John Cornthwaite ◽  
Fenglin Niu ◽  
Alan Levander ◽  
Michael Schmitz ◽  
Germán Prieto ◽  
...  
Keyword(s):  
South America ◽  
Seismic Anisotropy ◽  
P Wave ◽  
Large Igneous Province ◽  
Mantle Dynamics ◽  
Fast Axis ◽  
Shallow Subduction ◽  
Wave Tomography ◽  
Plate Coupling ◽  
Fast Polarization

<p>     The southernmost edge of the Caribbean (CAR) plate, a buoyant large igneous province, subducts shallowly beneath northwestern South America (NWSA) at a trench that lies northwest of Colombia. Recent finite frequency P-wave tomography results show a segmented CAR subducting at a shallow angle under the Santa Marta Massif to the Serrania de Perijá (SdP) before steepening while a detached segment beneath the Mérida Andes (MA) descends into the mantle transition zone. The dynamics of shallow subduction are poorly understood. Plate coupling between the flat subducting CAR and the overriding NWSA is proposed to have driven the uplift of the MA. In this study we analyze SKS shear wave splitting to investigate the seismic anisotropy beneath the slab segments to relate their geometry to mantle dynamics. We also use local S splitting to investigate the seismic anisotropy between the slab segments and the overriding plate. The data were recorded by a 65-element portable broadband seismograph network deployed in NWSA and 40 broadband stations of the Venezuelan and Colombian national seismograph networks.</p><p>     SKS fast polarization axes are measured generally trench-perpendicular (TP) west of the SdP but transition to trench-parallel (TL) at the SdP where the slab was imaged steepening into the mantle, consistent with previous studies. West of the MA the fast axis is again TP but transitions to TL under the MA. This second transition from TP to TL is likely due to mantle material being deflected around a detached slab under the MA. Local S fast polarization axes are dominantly TP throughout the study area west of the Santa Marta Massif and are consistent with slab-entrained flow. Under the Santa Marta Massif the fast axis is TL for reasons we do not yet understand.</p>

scholarly journals P wave tomography and anisotropy beneath Southeast Asia: Insight into mantle dynamics

2015 ◽  
Vol 120 (7) ◽  
pp. 5154-5174 ◽  
Author(s):  
Zhouchuan Huang ◽  
Dapeng Zhao ◽  
Liangshu Wang
Keyword(s):  
Southeast Asia ◽  
P Wave ◽  
Mantle Dynamics ◽  
Wave Tomography ◽  
Insight Into

scholarly journals Orogenic lithosphere and slabs in the greater Alpine area – interpretations based on teleseismic P-wave tomography

Solid Earth ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 2633-2669 ◽  
Author(s):  
Mark R. Handy ◽  
Stefan M. Schmid ◽  
Marcel Paffrath ◽  
Wolfgang Friederich ◽  
Keyword(s):  
Seismic Anisotropy ◽  
Pannonian Basin ◽  
Lower Boundary ◽  
Eastern Alps ◽  
P Wave ◽  
Moho Depth ◽  
Abrupt Decrease ◽  
Lateral Extrusion ◽  
Wave Tomography ◽  
The Alps

Abstract. Based on recent results of AlpArray, we propose a new model of Alpine collision that involves subduction and detachment of thick (∼ 180 km) European lithosphere. Our approach combines teleseismic P-wave tomography and existing local earthquake tomography (LET), allowing us to image the Alpine slabs and their connections with the overlying orogenic lithosphere at an unprecedented resolution. The images call into question the conventional notion that downward-moving lithosphere and slabs comprise only seismically fast lithosphere. We propose that the European lithosphere is heterogeneous, locally containing layered positive and negative Vp anomalies of up to 5 %–6 %. We attribute this layered heterogeneity to seismic anisotropy and/or compositional differences inherited from the Variscan and pre-Variscan orogenic cycles rather than to thermal anomalies. The lithosphere–asthenosphere boundary (LAB) of the European Plate therefore lies below the conventionally defined seismological LAB. In contrast, the lithosphere of the Adriatic Plate is thinner and has a lower boundary approximately at the base of strong positive Vp anomalies at 100–120 km. Horizontal and vertical tomographic slices reveal that beneath the central and western Alps, the European slab dips steeply to the south and southeast and is only locally still attached to the Alpine lithosphere. However, in the eastern Alps and Carpathians, this slab is completely detached from the orogenic crust and dips steeply to the north to northeast. This along-strike change in attachment coincides with an abrupt decrease in Moho depth below the Tauern Window, the Moho being underlain by a pronounced negative Vp anomaly that reaches eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted as representing hot upwelling asthenosphere that heated the overlying crust, allowing it to accommodate Neogene orogen-parallel lateral extrusion and thinning of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the east. A European origin of the northward-dipping, detached slab segment beneath the eastern Alps is likely since its down-dip length matches estimated Tertiary shortening in the eastern Alps accommodated by originally south-dipping subduction of European lithosphere. A slab anomaly beneath the Dinarides is of Adriatic origin and dips to the northeast. There is no evidence that this slab dips beneath the Alps. The slab anomaly beneath the Northern Apennines, also of Adriatic origin, hangs subvertically and is detached from the Apenninic orogenic crust and foreland. Except for its northernmost segment where it locally overlies the southern end of the European slab of the Alps, this slab is clearly separated from the latter by a broad zone of low Vp velocities located south of the Alpine slab beneath the Po Basin. Considered as a whole, the slabs of the Alpine chain are interpreted as highly attenuated, largely detached sheets of continental margin and Alpine Tethyan oceanic lithosphere that locally reach down to a slab graveyard in the mantle transition zone (MTZ).

scholarly journals Seismic anisotropy inferred from direct S-waves derived splitting measurements and its geodynamic implications beneath southeastern Tibetan Plateau

2016 ◽  
Author(s):  
Ashwani Kant Tiwari ◽  
Arun Singh ◽  
Tuna Eken ◽  
Nitin Grewal ◽  
Chandrani Singh
Keyword(s):  
Seismic Anisotropy ◽  
Plate Motion ◽  
Reference Station ◽  
Sharp Change ◽  
Lithospheric Deformation ◽  
Mantle Dynamics ◽  
Study Region ◽  
S Waves ◽  
Anisotropy Parameters ◽  
Fast Polarization

Abstract. The present study deals with detecting seismic anisotropy parameters beneath southeastern Tibet near Namche Barwa Mountain using splitting of the direct S-waves. We employed the reference station technique to remove the effects of source side anisotropy. Seismic anisotropy parameters, splitting time delay and fast polarization directions were estimated through analyses on a total of 501 splitting measurements obtained from direct-S waves from 25 earthquakes (> 5.5 magnitude) that were recorded at 42 stations of Namchebarwa seismic network. We observed a large variation in time delays ranging from 0.64 to 1.68 s but in most cases it is more than 1 s, which suggests for a highly anisotropic lithospheric mantle in the region. A comparison between direct S- and SKS-derived splitting parameters generally shows a close similarity although some discrepancies exist where null or negligible anisotropy is reported earlier using SKS. The seismic stations with hitherto null or negligible anisotropy are now supplemented with new measurements with clear anisotropic signatures. Our analyses indicate a sharp change in lateral variations of fast polarization directions (FPDs) from consistent ENE-SSW or E-W to NW-SE direction at the southeastern edge of Tibet. Comparison of the FPDs with global positioning system (GPS) measurements, absolute plate motion (APM) directions and surface geological features signify that the observed anisotropy and hence inferred deformation patterns are not only due to asthenospheric dynamics but it is a combination of lithospheric deformation and sub-lithospheric (asthenospheric) mantle dynamics. Splitting measurement using direct-S waves proves their utility to supplement the anisotropic measurements in the study region and fills the missing links that remain rather illusive due to lack of SKS measurements.

scholarly journals Subducted Lithosphere under South America from Multi-frequency P-wave Tomography

2021 ◽  
Author(s):  
Afsaneh Mohammadzaheri ◽  
Karin Sigloch ◽  
Kasra Hosseini
Keyword(s):  
South America ◽  
P Wave ◽  
Wave Tomography

3D shear velocity structure of the northwestern South America-Caribbean Subduction Zone from ambient noise and ballistic Rayleigh wave tomography

2021 ◽  
Author(s):  
Wenpei Miao ◽  
John Cornthwaite ◽  
Alan Levander ◽  
Fenglin Niu ◽  
Michael Schmitz ◽  
...  
Keyword(s):  
South America ◽  
Rayleigh Wave ◽  
Ambient Noise ◽  
Crustal Thickness ◽  
P Wave ◽  
Moho Depth ◽  
Good Resolution ◽  
Phase Velocities ◽  
Maracaibo Basin ◽  
Wave Tomography

<p>The Caribbean plate (CAR) collided with and initiated subduction beneath northwestern South America (SA) at about 60-55 Ma. Since the onset of subduction, it has formed the Lara nappes and subsequently the Laramide-style uplifts of the Merida Andes, Sierra de la Perija and Santa Marta ranges, with maximum elevations > 5km. The triangular Maracaibo block, bounded by the Santa Marta-Bucaramanga, Bocono and Oca-Ancon Faults, is currently escaping to the north relative to SA over both the subducting and nonsubducting elements of the CAR plate.</p><p>Although many petroleum related seismic studies have been done in this area, the details of the subduction geometry of the CAR plate beneath the Maracaibo block remain unclear. The few deeper seismic investigations are either very large scale, very local, or only peripheral to this area. Previous geodetic studies have suggested that this region has potential for a great (M~8+) earthquake (Bilham and Mencin, 2013). To investigate this complex region we fielded a 65 element broadband seismic array to complement the 48 existing stations of the Colombian and Venezuelan national seismic networks. The array is collectively referred to as the CARMArray.</p><p>In this study, we jointly inverted ambient noise Rayleigh wave Z/H ratios, phase velocities in the 8-30s band and ballistic Rayleigh wave phase velocities in 30-80s band to construct a 3D S-wave velocity model in the area from 75<sup>o</sup>-65<sup>o</sup> west and 5<sup>o</sup>-12<sup>o</sup> north. Rayleigh wave Z/H ratios are sensitive to the shallow sedimentary structure, while the phase velocity data have good resolution of the crust and upper mantle. The Vs model shows strong low-velocity anomalies beneath the Barinas-Apure and Maracaibo Basins, and the Paraguana Peninsula that are well correlated with surface geology. Sediment thickness beneath the Maracaibo basin reaches up to ~9 km depth, consistent with previous studies (Kellogg & Bonini, 1982). Crustal thickness beneath the Santa Marta uplift is 27-30 km, shallow for its nearly 4km elevation. From the trench to the southeast, Moho depth increases from 25-30 km near the coast to 40-45 km beneath the Maracaibo Basin, with the thickest crust, ~50 km, lying under the Merida Andes beneath the Bocono Fault. Crustal thickness decreases under the Venezeulan interior to ~45 km. From 50km to 150km depth, the CAR plate shows ~2% high Vs anomalies beneath the Santa Marta uplift and the Serrania de Perija range. Our slab image matches local slab seismicity very well (Cornthwaite et al., EGU 2021 GD7.1), and is consistent with and complements images from teleseismic P-wave tomography (Cornthwaite et al, 2021, submitted).</p>

scholarly journals High mantle seismic P-wave speeds as a signature for gravitational spreading of superplumes

2020 ◽  
Vol 6 (22) ◽  
pp. eaba7118 ◽  
Author(s):  
Tim Stern ◽  
Simon Lamb ◽  
James D. P. Moore ◽  
David Okaya ◽  
Katharina Hochmuth
Keyword(s):  
Upper Mantle ◽  
Thermal Effects ◽  
Seismic Anisotropy ◽  
P Wave ◽  
Large Igneous Province ◽  
Wave Speeds ◽  
Horizontal Length ◽  
Igneous Province ◽  
Radial Anisotropy

New passive- and active-source seismic experiments reveal unusually high mantle P-wave speeds that extend beneath the remnants of the world’s largest known large igneous province, making up the 120-million-year-old Ontong-Java-Manihiki-Hikurangi Plateau. Sub-Moho Pn phases of ~8.8 ± 0.2 km/s are resolved with negligible azimuthal seismic anisotropy, but with strong radial anisotropy (~10%), characteristic of aggregates of olivine with an AG crystallographic fabric. These seismic results are the first in situ evidence for this fabric in the upper mantle. We show that its presence can be explained by isotropic horizontal dilation and vertical flattening due to late-stage gravitational collapse and spreading in the top 10 to 20 km of a depleted, mushroom-shaped, superplume head on a horizontal length scale of 1000 km or more. This way, it provides a seismic tool to track plumes long after the thermal effects have ceased.

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