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Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography

Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography
Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography
The Costa Rica–Nicaragua subduction zone shows systematic along strike variation in arc chemistry, geology, tectonics and seismic velocity and attenuation, presenting global extremes within a few hundred kilometres. In this study, we use teleseismic and ambient noise derived surface wave tomography to produce a 3-D shear velocity model of the region. We use the 48 stations of the TUCAN array, and up to 94 events for the teleseismic Rayleigh wave inversion, and 18 months of continuous data for cross correlation to estimate Green's functions from ambient noise. In the shallow crust (0–15?km) we observe low-shear velocities directly beneath the arc volcanoes (<3?km s–1) and higher velocities in the backarc of Nicaragua. The anomalies below the volcanoes are likely caused by heated crust, intruded by magma. We estimate crustal thickness by picking the depth to the 4?km s–1 velocity contour. We infer >40-km-thick crust beneath the Costa Rican arc and the Nicaraguan Highlands, thinned crust (?20?km) beneath the Nicaraguan Depression, and increasing crustal thickness in the backarc region, consistent with receiver function studies. The region of thinned, seismically slow and likely weakened crust beneath the arc in Nicaragua is not localizing deformation associated with oblique subduction. At mantle depths (55–120?km depth) we observe lower shear velocities (up to 3?per?cent) beneath the Nicaraguan arc and backarc than beneath Costa Rica. Our low-shear velocity anomaly beneath Nicaragua is in the same location as a low-shear velocity anomaly and displaced towards the backarc from the high VP/VS anomaly observed in body wave tomography. The lower shear velocity beneath Nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab or higher temperature. Finally, we observe a linear high-velocity region at depths >120?km parallel to the trench, which is consistent with the subducting slab.
Tomography Interferometry Surface waves and free oscillations Seismic Tomography Subduction zone processes Volcanic arc processes
0956-540X
1300-1313
Harmon, N.
10d11a16-b8b0-4132-9354-652e72d8e830
de la Cruz, M.S.
f838d765-8cbc-4d11-afa9-90e805d06999
Rychert, C.A.
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Abers, G.
a22b8f83-cad4-4076-abc9-da758d175df3
Fischer, K.
2a93b145-67ca-4ccb-b852-4c203e0d6e33
Harmon, N.
10d11a16-b8b0-4132-9354-652e72d8e830
de la Cruz, M.S.
f838d765-8cbc-4d11-afa9-90e805d06999
Rychert, C.A.
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Abers, G.
a22b8f83-cad4-4076-abc9-da758d175df3
Fischer, K.
2a93b145-67ca-4ccb-b852-4c203e0d6e33

Harmon, N., de la Cruz, M.S., Rychert, C.A., Abers, G. and Fischer, K. (2013) Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography. Geophysical Journal International, 195 (2), 1300-1313. (doi:10.1093/gji/ggt309).

Record type: Article

Abstract

The Costa Rica–Nicaragua subduction zone shows systematic along strike variation in arc chemistry, geology, tectonics and seismic velocity and attenuation, presenting global extremes within a few hundred kilometres. In this study, we use teleseismic and ambient noise derived surface wave tomography to produce a 3-D shear velocity model of the region. We use the 48 stations of the TUCAN array, and up to 94 events for the teleseismic Rayleigh wave inversion, and 18 months of continuous data for cross correlation to estimate Green's functions from ambient noise. In the shallow crust (0–15?km) we observe low-shear velocities directly beneath the arc volcanoes (<3?km s–1) and higher velocities in the backarc of Nicaragua. The anomalies below the volcanoes are likely caused by heated crust, intruded by magma. We estimate crustal thickness by picking the depth to the 4?km s–1 velocity contour. We infer >40-km-thick crust beneath the Costa Rican arc and the Nicaraguan Highlands, thinned crust (?20?km) beneath the Nicaraguan Depression, and increasing crustal thickness in the backarc region, consistent with receiver function studies. The region of thinned, seismically slow and likely weakened crust beneath the arc in Nicaragua is not localizing deformation associated with oblique subduction. At mantle depths (55–120?km depth) we observe lower shear velocities (up to 3?per?cent) beneath the Nicaraguan arc and backarc than beneath Costa Rica. Our low-shear velocity anomaly beneath Nicaragua is in the same location as a low-shear velocity anomaly and displaced towards the backarc from the high VP/VS anomaly observed in body wave tomography. The lower shear velocity beneath Nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab or higher temperature. Finally, we observe a linear high-velocity region at depths >120?km parallel to the trench, which is consistent with the subducting slab.

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More information

Published date: November 2013
Keywords: Tomography Interferometry Surface waves and free oscillations Seismic Tomography Subduction zone processes Volcanic arc processes
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 361096
URI: http://eprints.soton.ac.uk/id/eprint/361096
ISSN: 0956-540X
PURE UUID: 120416a7-734e-4665-9517-21c58e81b69b
ORCID for N. Harmon: ORCID iD orcid.org/0000-0002-0731-768X

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Date deposited: 13 Jan 2014 10:27
Last modified: 15 Mar 2024 03:33

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Contributors

Author: N. Harmon ORCID iD
Author: M.S. de la Cruz
Author: C.A. Rychert
Author: G. Abers
Author: K. Fischer

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