Complex seismic anisotropy in Madagascar revealed by shear wave splitting measurements

Cristo Ramirez, Andrew Arnold Nyblade, Michael E. Wysession, Martin Pratt, Fenitra Andriampenomanana, Tsiriandrimanana Rakotondraibe

Research output: Contribution to journalArticle

Abstract

Shear wave fast polarization directions (Φ) and delay times (dt) obtained from SKS and SKKS splitting measurements are reported for 25 temporary and 2 permanent seismic stations distributed throughout Madagascar. Results show a complicated pattern of Φ that is not easily explained by a single source of anisotropy, such as fossil anisotropy in the lithosphere or mantle flow from the African superplume or absolute plate motion. To interpret the results, we divide the island into four areas. The northern part of the island is characterized by an ~ENE-WSW Φ pattern, which can be attributed to NE-oriented mantle flow from the African superplume or plate motion modified by SE-oriented mantle flow from the Comoros hotspot. In the centre of the island, a roughly circular Φ pattern is observed and can be attributed to upwelling asthenosphere, caused by lithospheric delamination, interacting with mantle flow from the superplume or plate motion. Small-scale mantle flow can also be invoked to explain a separate semi-circular Φ pattern in the southwestern part of the island. In the south-central and southeastern parts of the island, Φ is parallel to the NW strike of shear zones at many stations and can be attributed to fossil anisotropy in the lithosphere. However, NE-oriented fast polarization directions along the northern edge of this area do not align with the orientation of shear zones and could instead be part of the circular Φ pattern that characterizes the central part of the island.

Original languageEnglish (US)
Pages (from-to)1718-1727
Number of pages10
JournalGeophysical Journal International
Volume215
Issue number3
DOIs
StatePublished - Dec 1 2018

Fingerprint

Madagascar
seismic anisotropy
wave splitting
Shear waves
S waves
S-wave
Anisotropy
Earth mantle
anisotropy
mantle
plate motion
Polarization
fossils
Delamination
lithosphere
shear zone
Time delay
polarization
stations
fossil

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

Ramirez, C., Nyblade, A. A., Wysession, M. E., Pratt, M., Andriampenomanana, F., & Rakotondraibe, T. (2018). Complex seismic anisotropy in Madagascar revealed by shear wave splitting measurements. Geophysical Journal International, 215(3), 1718-1727. https://doi.org/10.1093/gji/ggy367
Ramirez, Cristo ; Nyblade, Andrew Arnold ; Wysession, Michael E. ; Pratt, Martin ; Andriampenomanana, Fenitra ; Rakotondraibe, Tsiriandrimanana. / Complex seismic anisotropy in Madagascar revealed by shear wave splitting measurements. In: Geophysical Journal International. 2018 ; Vol. 215, No. 3. pp. 1718-1727.
@article{448be7ab2e6c40cfa729732ebc61b1ce,
title = "Complex seismic anisotropy in Madagascar revealed by shear wave splitting measurements",
abstract = "Shear wave fast polarization directions (Φ) and delay times (dt) obtained from SKS and SKKS splitting measurements are reported for 25 temporary and 2 permanent seismic stations distributed throughout Madagascar. Results show a complicated pattern of Φ that is not easily explained by a single source of anisotropy, such as fossil anisotropy in the lithosphere or mantle flow from the African superplume or absolute plate motion. To interpret the results, we divide the island into four areas. The northern part of the island is characterized by an ~ENE-WSW Φ pattern, which can be attributed to NE-oriented mantle flow from the African superplume or plate motion modified by SE-oriented mantle flow from the Comoros hotspot. In the centre of the island, a roughly circular Φ pattern is observed and can be attributed to upwelling asthenosphere, caused by lithospheric delamination, interacting with mantle flow from the superplume or plate motion. Small-scale mantle flow can also be invoked to explain a separate semi-circular Φ pattern in the southwestern part of the island. In the south-central and southeastern parts of the island, Φ is parallel to the NW strike of shear zones at many stations and can be attributed to fossil anisotropy in the lithosphere. However, NE-oriented fast polarization directions along the northern edge of this area do not align with the orientation of shear zones and could instead be part of the circular Φ pattern that characterizes the central part of the island.",
author = "Cristo Ramirez and Nyblade, {Andrew Arnold} and Wysession, {Michael E.} and Martin Pratt and Fenitra Andriampenomanana and Tsiriandrimanana Rakotondraibe",
year = "2018",
month = "12",
day = "1",
doi = "10.1093/gji/ggy367",
language = "English (US)",
volume = "215",
pages = "1718--1727",
journal = "Geophysical Journal International",
issn = "0956-540X",
publisher = "Wiley-Blackwell",
number = "3",

}

Ramirez, C, Nyblade, AA, Wysession, ME, Pratt, M, Andriampenomanana, F & Rakotondraibe, T 2018, 'Complex seismic anisotropy in Madagascar revealed by shear wave splitting measurements', Geophysical Journal International, vol. 215, no. 3, pp. 1718-1727. https://doi.org/10.1093/gji/ggy367

Complex seismic anisotropy in Madagascar revealed by shear wave splitting measurements. / Ramirez, Cristo; Nyblade, Andrew Arnold; Wysession, Michael E.; Pratt, Martin; Andriampenomanana, Fenitra; Rakotondraibe, Tsiriandrimanana.

In: Geophysical Journal International, Vol. 215, No. 3, 01.12.2018, p. 1718-1727.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Complex seismic anisotropy in Madagascar revealed by shear wave splitting measurements

AU - Ramirez, Cristo

AU - Nyblade, Andrew Arnold

AU - Wysession, Michael E.

AU - Pratt, Martin

AU - Andriampenomanana, Fenitra

AU - Rakotondraibe, Tsiriandrimanana

PY - 2018/12/1

Y1 - 2018/12/1

N2 - Shear wave fast polarization directions (Φ) and delay times (dt) obtained from SKS and SKKS splitting measurements are reported for 25 temporary and 2 permanent seismic stations distributed throughout Madagascar. Results show a complicated pattern of Φ that is not easily explained by a single source of anisotropy, such as fossil anisotropy in the lithosphere or mantle flow from the African superplume or absolute plate motion. To interpret the results, we divide the island into four areas. The northern part of the island is characterized by an ~ENE-WSW Φ pattern, which can be attributed to NE-oriented mantle flow from the African superplume or plate motion modified by SE-oriented mantle flow from the Comoros hotspot. In the centre of the island, a roughly circular Φ pattern is observed and can be attributed to upwelling asthenosphere, caused by lithospheric delamination, interacting with mantle flow from the superplume or plate motion. Small-scale mantle flow can also be invoked to explain a separate semi-circular Φ pattern in the southwestern part of the island. In the south-central and southeastern parts of the island, Φ is parallel to the NW strike of shear zones at many stations and can be attributed to fossil anisotropy in the lithosphere. However, NE-oriented fast polarization directions along the northern edge of this area do not align with the orientation of shear zones and could instead be part of the circular Φ pattern that characterizes the central part of the island.

AB - Shear wave fast polarization directions (Φ) and delay times (dt) obtained from SKS and SKKS splitting measurements are reported for 25 temporary and 2 permanent seismic stations distributed throughout Madagascar. Results show a complicated pattern of Φ that is not easily explained by a single source of anisotropy, such as fossil anisotropy in the lithosphere or mantle flow from the African superplume or absolute plate motion. To interpret the results, we divide the island into four areas. The northern part of the island is characterized by an ~ENE-WSW Φ pattern, which can be attributed to NE-oriented mantle flow from the African superplume or plate motion modified by SE-oriented mantle flow from the Comoros hotspot. In the centre of the island, a roughly circular Φ pattern is observed and can be attributed to upwelling asthenosphere, caused by lithospheric delamination, interacting with mantle flow from the superplume or plate motion. Small-scale mantle flow can also be invoked to explain a separate semi-circular Φ pattern in the southwestern part of the island. In the south-central and southeastern parts of the island, Φ is parallel to the NW strike of shear zones at many stations and can be attributed to fossil anisotropy in the lithosphere. However, NE-oriented fast polarization directions along the northern edge of this area do not align with the orientation of shear zones and could instead be part of the circular Φ pattern that characterizes the central part of the island.

UR - http://www.scopus.com/inward/record.url?scp=85054738420&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85054738420&partnerID=8YFLogxK

U2 - 10.1093/gji/ggy367

DO - 10.1093/gji/ggy367

M3 - Article

AN - SCOPUS:85054738420

VL - 215

SP - 1718

EP - 1727

JO - Geophysical Journal International

JF - Geophysical Journal International

SN - 0956-540X

IS - 3

ER -