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The Use of Azimuthal Variation in ScS–S Differential Travel Times to Investigate Possible Anisotropy in the Lowermost Mantle Beneath the Philippines

We collected approximately 500 ScS–S differential travel times passing beneath the Philippines with various azimuths to discuss whether there were azimuthal variations in the ScS–S time residuals. By correcting for mantle heterogeneity using a three-dimensional (3D) mantle velocity model, we found a large variance reduction in the ScS–S residuals. In addition, the strong negative correlation between the S and ScS–S time residuals was greatly reduced, while the positive correlation between the ScS and ScS–S time residuals moderately improved, indicating that the corrected ScS–S residuals are manifestations of the lower half of the lower mantle structure. Next, we corrected for the local-scale heterogeneity in the lower mantle by subtracting the bin-averaged ScS–S residuals, and we experimented with fitting the trigonometric functions in terms of the propagation azimuth ? to the ScS–S residuals, suggesting that a 2? variation is significant. If we accept the hypothesis of azimuthal anisotropy in the lowermost mantle, the fastest direction of the S-wave velocity was east-southeast–west-northwest (N97.5° E– N82.5° W), and the amplitude of the azimuthal anisotropy was approximately 1.4% anisotropy if we assume a D? thickness of 300 km.

Ketersediaan
#
Perpustakaan BIG (Eksternal Harddisk) 550
409
Tersedia
Informasi Detail
Judul Seri
Geosciences
No. Panggil
550
Penerbit
Switzerland : MPDI.,
Deskripsi Fisik
21 hlm PDF, 3.139 KB
Bahasa
Inggris
ISBN/ISSN
2076-3263
Klasifikasi
550
Tipe Isi
text
Tipe Media
-
Tipe Pembawa
online resource
Edisi
Vol.15, Issue 2, February 2025
Subjek
Philippines
azimuthal anisotropy
lower mantle
ScS–S travel times
Info Detail Spesifik
Geosciences
Pernyataan Tanggungjawab
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  • The Use of Azimuthal Variation in ScS–S Differential Travel Times to Investigate Possible Anisotropy in the Lowermost Mantle Beneath the Philippines
    We collected approximately 500 ScS–S differential travel times passing beneath the Philippines with various azimuths to discuss whether there were azimuthal variations in the ScS–S time residuals. By correcting for mantle heterogeneity using a three-dimensional (3D) mantle velocity model, we found a large variance reduction in the ScS–S residuals. In addition, the strong negative correlation between the S and ScS–S time residuals was greatly reduced, while the positive correlation between the ScS and ScS–S time residuals moderately improved, indicating that the corrected ScS–S residuals are manifestations of the lower half of the lower mantle structure. Next, we corrected for the local-scale heterogeneity in the lower mantle by subtracting the bin-averaged ScS–S residuals, and we experimented with fitting the trigonometric functions in terms of the propagation azimuth θ to the ScS–S residuals, suggesting that a 2θ variation is significant. If we accept the hypothesis of azimuthal anisotropy in the lowermost mantle, the fastest direction of the S-wave velocity was east-southeast–west-northwest (N97.5° E– N82.5° W), and the amplitude of the azimuthal anisotropy was approximately 1.4% anisotropy if we assume a D″ thickness of 300 km.
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