Joint-Interpretation of SKS Splitting Measurements and Receiver Function Data for Detecting Seismic Anisotropy in the Upper Mantle: Feasibility and Limitations.

Author(s)

G. Lamarque, N. Piana Agostinetti, J. Julià, S. Philippe, M. Evain

Abstract

Measuring seismic anisotropy within the Earth is essential as it

constitutes a proxy for inferring lithospheric deformation and

asthenospheric mantle flows that develops preferred orientations of the

minerals in response to tectonic strain. The most commonly used method

to detect anisotropy beneath a seismic station is the measurement of

teleseismic SKS wave splitting, in which the delay time (δt)

between two fast- and slow- shear-waves and their orientation of

polarization (Φ) are determined from two horizontal recordings. This

technique provides integrated estimates (SKS data, hereinafter) of the

average Φ and δt along the entire SKS ray-path. Despite its

importance for large-scale anisotropy within the upper mantle, the

analysis of SKS data suffers from several limitations : (1) SKS data are

difficult to interpret in regions where several anisotropic layers

occur; (2) SKS waves fail to provide robust information about anisotropy

related to thin layers; and (3) SKS data can investigate rock volumes

with an horizontal symmetry axis only. During the last decade a new

method, called harmonic decomposition of teleseismic Receiver Functions

(RFs) has been developed in order to detect more complex anisotropic

layering. This methodology is based on the extraction of back-azimuth

harmonics of the RF dataset. Briefly, it constitutes a tool to

appreciate the value of Φ and δt at every depth-level

affording a detailed study of the rock anisotropy with both plunging and

horizontal symmetry axis. RFs studies are however commonly limited to

the first 10-15s of the signal and do not sample the anisotropy at large

depths. In this work we investigate in details both SKS data and RFs

harmonic decomposition for a pool of stations deployed in northeastern

Brasil, in order to understand how results from the analysis of these

two observables can be jointly interpreted. Our study focuses on the

permanent GSN station (RCBR) and on a number of temporary seismic

stations available in the area. We show that comparison and/or joint

interpretation is not straightforward as both results can vary according

to the amount of data available and their distribution in back-azimuth,

and filtering. However, if those shortcomings can be fully accounted

for, the integration of these two observables may result in robust

detection of upper mantle anisotropy.

Organisation(s)

Department of Geology

External organisation(s)

Centre de Bretagne, Universidade Federal do Rio Grande do Norte, Centro Nazionale Terremoti

Publication date

12-2018

Peer reviewed

Yes

Austrian Fields of Science 2012

105102 General geophysics

Keywords

Portal url

https://ucrisportal.univie.ac.at/en/publications/943130b9-79a8-46c4-b8d1-ce791272c12e