TY - JOUR
T1 - Complex seismic anisotropy in Madagascar revealed by shear wave splitting measurements
AU - Ramirez, Cristo
AU - Nyblade, Andrew
AU - Wysession, Michael E.
AU - Pratt, Martin
AU - Andriampenomanana, Fenitra
AU - Rakotondraibe, Tsiriandrimanana
N1 - Funding Information:
We gratefully acknowledge the work of the reviewers of this manuscript for their helpful comments and improvements. Figures in this paper have been produced with the GMT software (Wessel & Smith 1998). This research was funded by the National Science Foundation, through grants EAR-0838426 and 0838387. The facilities of IRIS Data Services, and specifically the IRIS Data Management Center, were used for access to waveforms, related metadata, and/or derived products used in this study. IRIS Data Services are funded through the Seismological Facilities for the Advancement of Geoscience and EarthScope (SAGE) Proposal of the National Science Foundation under Cooperative Agreement EAR 1261681.
Publisher Copyright:
© The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society.
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.
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U2 - 10.1093/gji/ggy367
DO - 10.1093/gji/ggy367
M3 - Article
AN - SCOPUS:85054738420
SN - 0956-540X
VL - 215
SP - 1718
EP - 1727
JO - Geophysical Journal International
JF - Geophysical Journal International
IS - 3
ER -