Advanced search
Start date
Betweenand
(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Comparing ray-theoretical and finite-frequency teleseismic traveltimes: implications for constraining the ratio of S-wave to P-wave velocity variations in the lower mantle

Full text
Author(s):
Chaves, Carlos A. M. [1, 2] ; Ritsema, Jeroen [2] ; Koelemeijer, Paula [3]
Total Authors: 3
Affiliation:
[1] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Dept Geofis, Rua Matao 1226, BR-05508090 Sao Paulo - Brazil
[2] Univ Michigan, Dept Earth & Environm Sci, 1100 North Univ Ave, Ann Arbor, MI 48109 - USA
[3] Royal Holloway Univ London, Dept Earth Sci, Egham TW20 0EX, Surrey - England
Total Affiliations: 3
Document type: Journal article
Source: Geophysical Journal International; v. 224, n. 3, p. 1540-1552, MAR 2021.
Web of Science Citations: 0
Abstract

A number of seismological studies have indicated that the ratio R of S-wave and P-wave velocity perturbations increases to 3-4 in the lower mantle with the highest values in the large low-velocity provinces (LLVPs) beneath Africa and the central Pacific. Traveltime constraints on R are based primarily on ray-theoretical modelling of delay times of P waves (Delta T-P) and S waves (Delta T-S), even for measurements derived from long-period waveforms and core-diffracted waves for which ray theory (RT) is deemed inaccurate. Along with a published set of traveltime delays, we compare predicted values of Delta T-P, Delta T-S, and the Delta T-S/Delta T-P ratio for RT and finite-frequency (FF) theory to determine the resolvability of R in the lower mantle. We determine the FF predictions of Delta T-P and Delta T-S using cross-correlation methods applied to spectral-element method waveforms, analogous to the analysis of recorded waveforms, and by integration using FF sensitivity kernels. Our calculations indicate that RT and FF predict a similar variation of the Delta T-S/Delta T-P ratio when R increases linearly with depth in the mantle. However, variations of R in relatively thin layers (< 400 km) are poorly resolved using long-period data (T > 20 s). This is because FF predicts that Delta T-P and Delta T-S vary smoothly with epicentral distance even when vertical P-wave and S-wave gradients change abruptly. Our waveform simulations also show that the estimate of R for the Pacific LLVP is strongly affected by velocity structure shallower in the mantle. If R increases with depth in the mantle, which appears to be a robust inference, the acceleration of P waves in the lithosphere beneath eastern North America and the high-velocity Farallon anomaly negates the P-wave deceleration in the LLVP. This results in a Delta T-P of about 0, whereas Delta T-S is positive. Consequently, the recorded high Delta T-S/Delta T-P for events in the southwest Pacific and stations in North America may be misinterpreted as an anomalously high R for the Pacific LLVP. (AU)

FAPESP's process: 14/17779-3 - Global study of the mantle transition zone structure from geoid anomalies and SS wave propagation
Grantee:Carlos Alberto Moreno Chaves
Support type: Scholarships in Brazil - Post-Doctorate
FAPESP's process: 16/11580-6 - Global study of the mantle transition zone structure from SS wave propagation.
Grantee:Carlos Alberto Moreno Chaves
Support type: Scholarships abroad - Research Internship - Post-doctor