Shear-wave attenuation anisotropy: a new constraint on mantle melt near the Main Ethiopian Rift




The behaviour of fluids in preferentially aligned fractures plays an important role in a range of dynamic processes within the Earth. In the near-surface, understanding systems of fluid-filled fractures is crucial for applications such as geothermal energy production, monitoring CO2 storage sites, and exploration for metalliferous sub-volcanic brines. Mantle melting is a key geodynamic process, exerting control over its composition and dynamic processes. Upper mantle melting weakens the lithosphere, facilitating rifting and other surface expressions of tectonic processes.
Aligned fluid-filled fractures are an efficient mechanism for seismic velocity anisotropy, requiring very low volume fractions, but such rock physics models also predict significant shear-wave attenuation anisotropy. In comparison, the attenuation anisotropy expected for crystal preferred orietation mechanisms is negligible or would only operate outside of the seismic frequency band.
Here we demonstrate a new method for measuring shear-wave attenuation anisotropy, apply it to synthetic examples, and make the first measurements of SKS attenuation anisotropy using data recorded at the station FURI, in Ethiopia. At FURI we measure attenuation anisotropy where the fast shear-wave has been more attenuated than the slow shear-wave. This can be explained by the presence of aligned fluids, most probably melts, in the upper mantle using a poroelastic squirt flow model. Modelling of this result suggests that a 1% melt fraction, hosted in aligned fractures dipping ca. 40° that strike perpendicular to the Main Ethiopian Rift, is required to explain the observed attenuation anisotropy. This agrees with previous SKS shear-wave splitting analysis which suggested a 1% melt fraction beneath FURI. The interpreted fracture strike and dip, however, disagrees with previous work in the region which interprets sub-vertical melt inclusions aligned parallel to the Main Ethiopian Rift which only produce attenuation anisotropy where the slow shear-wave is more attenuated. These results show that attenuation anisotropy could be a useful tool for detecting mantle melt, and may offer strong constraints on the extent and orientation of melt inclusions which cannot be achieved from seismic velocity anisotropy alone.


Abramson, E. H., Brown, J. M., Slutsky, L. J., & Zaug, J. (1997). The elastic constants of San Carlos olivine to 17 GPa. Journal of Geophysical Research: Solid Earth, 102(B6), 12253–12263.

Aki, K., & Richards, P. G. (1980). Quantitative Seismology — Theory and Methods (A. Cox, Ed.; Vol. 1, pp. 170–182). W.H. Freeman.

Albuquerque Seismological Laboratory/USGS. (2014). Global Seismograph Network (GSN - IRIS/USGS). International Federation of Digital Seismograph Networks.

Al‐Harrasi, O. H., Kendall, J. ‐M., & Chapman, M. (2011). Fracture characterization using frequency‐dependent shear wave anisotropy analysis of microseismic data. Geophysical Journal International, 185(2), 1059–1070.

Asplet, J, Wookey, J., Kendall, M., Chapman, M., & Das, R. (2023). Suppplementary material for Shear-wave attenuation anisotropy: a fluid detection tool.

Asplet, Joseph, Wookey, J., & Kendall, M. (2022). Inversion of shear wave waveforms reveal deformation in the lowermost mantle. Geophysical Journal International, 232(1), 97–114.

Ayele, A., Stuart, G., & Kendall, J. ‐Michael. (2004). Insights into rifting from shear wave splitting and receiver functions: an example from Ethiopia. Geophysical Journal International, 157(1), 354–362.

Backus, G. E. (1962). Long‐wave elastic anisotropy produced by horizontal layering. Journal of Geophysical Research, 67(11), 4427–4440.

Bacon, C. A., Johnson, J. H., White, R. S., & Rawlinson, N. (2022). On the Origin of Seismic Anisotropy in the Shallow Crust of the Northern Volcanic Zone, Iceland. Journal of Geophysical Research: Solid Earth, 127(1).

Baird, A. F., Kendall, J.-M., & Angus, D. A. (2013). Frequency-dependent seismic anisotropy due to fractures: Fluid flow versus scatteringFrequency-dependent anisotropy. Geophysics, 78(2), WA111–WA122.

Baird, A. F., Kendall, J.-M., Sparks, R. S. J., & Baptie, B. (2015). Transtensional deformation of Montserrat revealed by shear wave splitting. Earth and Planetary Science Letters, 425, 179–186.

Barnes, A. E. (1993). Instantaneous spectral bandwidth and dominant frequency with applications to seismic reflection data. Geophysics, 58(3), 419–428.

Bastow, I. D., Nyblade, A. A., Stuart, G. W., Rooney, T. O., & Benoit, M. H. (2008). Upper mantle seismic structure beneath the Ethiopian hot spot: Rifting at the edge of the African low‐velocity anomaly. Geochemistry, Geophysics, Geosystems, 9(12).

Bastow, I. D., Pilidou, S., Kendall, J.-M., & Stuart, G. W. (n.d.). Melt-induced seismic anisotropy and magma assisted rifting in Ethiopia: Evidence from surface waves. Geochemistry, Geophysics, Geosystems, 11(6).

Best, A. I., Sothcott, J., & McCann, C. (2007). A laboratory study of seismic velocity and attenuation anisotropy in near‐surface sedimentary rocks [Journal Article]. Geophysical Prospecting, 55(5), 609–625.

Beyreuther, M., Barsch, R., Krischer, L., Megies, T., Behr, Y., & Wassermann, J. (2010). ObsPy: A Python Toolbox for Seismology. Seismological Research Letters, 81(3), 530–533.

Buck, W. R. (2004). 1. Consequences of Asthenospheric Variability on Continental Rifting. In G. D. Karner, B. Taylor, N. W. Driscoll, & D. L. Kohlstedt (Eds.), Rheology and Deformation of the Lithosphere at Continental Margins (pp. 1–30). Columbia University Press.

Carter, A. J., & Kendall, J. ‐Michael. (2006). Attenuation anisotropy and the relative frequency content of split shear waves. Geophysical Journal International, 165(3), 865–874.

Červenỳ, V., Molotkov, I. A., & Pšenčı́k, I. (1977). Ray method in seismology (pp. 47–50). Universita Karlova.

Chambers, E. L., Harmon, N., Keir, D., & Rychert, C. A. (2019). Using Ambient Noise to Image the Northern East African Rift. Geochemistry, Geophysics, Geosystems, 20(4), 2091–2109.

Chambers, E. L., Harmon, N., Rychert, C. A., Gallacher, R. J., & Keir, D. (2022). Imaging the seismic velocity structure of the crust and upper mantle in the northern East African Rift using Rayleigh wave tomography. Geophysical Journal International, 230(3), ggac156-.

Chapman, M. (2003). Frequency‐dependent anisotropy due to meso‐scale fractures in the presence of equant porosity. Geophysical Prospecting, 51(5), 369–379.

Chapman, M., Maultzsch, S., & Liu, E. (2003). Some Estimates of the Squirt-flow Frequency. All Days, SEG-2003-1290.

Chevrot, S. (2000). Multichannel analysis of shear wave splitting. Journal of Geophysical Research: Solid Earth, 105(B9), 21579–21590.

Crampin, S. (1981). A review of wave motion in anisotropic and cracked elastic-media. Wave Motion, 3(4), 343–391.

Crampin, S. (1984). Effective anisotropic elastic constants for wave propagation through cracked solids. Geophysical Journal of the Royal Astronomical Society, 76(1), 135–145.

Dasios, A., Astin, T. R., & McCann, C. (2001). Compressional‐wave Q estimation from full‐waveform sonic data. Geophysical Prospecting, 49(3), 353–373.

Durand, S., Matas, J., Ford, S., Ricard, Y., Romanowicz, B., & Montagner, J.-P. (2013). Insights from ScS–S measurements on deep mantle attenuation. Earth and Planetary Science Letters, 374, 101–110.

Engelhard, L. (1996). Determination of Seismic‐Wave Attenuation By Complex Trace Analysis. Geophysical Journal International, 125(2), 608–622.

Eshelby, J. D. (1957). The determination of the elastic field of an ellipsoidal inclusion, and related problems. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 241(1226), 376–396.

Eshetu, A., Mammo, T., & Tilmann, F. (2021). Imaging the Ethiopian Rift Region Using Transdimensional Hierarchical Seismic Noise Tomography. Pure and Applied Geophysics, 178(11), 4367–4388.

Ford, H. A., Goldhagen, G., Byrnes, J. S., & Brounce, M. N. (2022). New Insight into the Physical Properties of the East African Mantle from Seismic Attenuation. AGU Fall Meeting Abstracts, 2022, eT43B-03.

Ford, S. R., Garnero, E. J., & Thorne, M. S. (2012). Differential t* measurements via instantaneous frequency matching: observations of lower mantle shear attenuation heterogeneity beneath western Central America. Geophysical Journal International, 189(1), 513–523.

Futterman, W. I. (1962). Dispersive body waves. Journal of Geophysical Research (1896-1977), 67(13), 5279–5291.

Gabor, D. (1946). Theory of Communication. Journal of the Institution of Electrical Engineers, 93(26), 429–441.

Galvin, R. J., & Gurevich, B. (2009). Effective properties of a poroelastic medium containing a distribution of aligned cracks. Journal of Geophysical Research: Solid Earth, 114(B7).

Galvin, Robert J., & Gurevich, B. (2015). Frequency‐dependent anisotropy of porous rocks with aligned fractures. Geophysical Prospecting, 63(1), 141–150.

Hall, S. A., Kendall, J. M., & Baan, M. van der. (2004). Some comments on the effects of lower-mantle anisotropy on SKS and SKKS phases. Physics of the Earth and Planetary Interiors, 146(3–4), 469–481.

Hammond, J. O. S., Kendall, J. ‐M., Wookey, J., Stuart, G. W., Keir, D., & Ayele, A. (2014). Differentiating flow, melt, or fossil seismic anisotropy beneath Ethiopia. Geochemistry, Geophysics, Geosystems, 15(5), 1878–1894.

Hammond, W. C., & Humphreys, E. D. (2000). Upper mantle seismic wave attenuation: Effects of realistic partial melt distribution. Journal of Geophysical Research: Solid Earth, 105(B5), 10987–10999.

Holtzman, B. K., & Kendall, J. ‐Michael. (2010). Organized melt, seismic anisotropy, and plate boundary lubrication. Geochemistry, Geophysics, Geosystems, 11(12), n/a-n/a.

Hudson, J. A. (1980). Overall properties of a cracked solid. Mathematical Proceedings of the Cambridge Philosophical Society, 88(2), 371–384.

Hudson, J. A. (1981). Wave speeds and attenuation of elastic waves in material containing cracks. Geophysical Journal of the Royal Astronomical Society, 64(1), 133–150.

Hudson, J. A., Liu, E., & Crampin, S. (1996). The mechanical properties of materials with interconnected cracks and pores. Geophysical Journal International, 124(1), 105–112.

Hudson, T. S., Asplet, J., & Walker, A. (2023). Automated shear-wave splitting analysis for single- and multi- layer anisotropic media. Seismica.

Hunter, J. D. (2007). Matplotlib: A 2D graphics environment. Computing in Science & Engineering, 9(3), 90–95.

International Seismological Centre. (2023). ISC Bulletin.

Jakobsen, M., Johansen, T. A., & McCann, C. (2003). The acoustic signature of fluid flow in complex porous media. Journal of Applied Geophysics, 54(3–4), 219–246.

Jin, Z., Chapman, M., & Papageorgiou, G. (2018). Frequency-dependent anisotropy in a partially saturated fractured rock. Geophysical Journal International, 215(3), 1985–1998.

Kendall, J.-M., Stuart, G. W., Ebinger, C. J., Bastow, I. D., & Keir, D. (2005). Magma-assisted rifting in Ethiopia. Nature, 433(7022), 146–148.

Kendall, John-Michael. (2000). Seismic anisotropy in the boundary layers of the mantle. In S. Karato, A. Forte, R. Liebermann, G. Masters, & L. Stixtrude (Eds.), Earth’s Deep Interior: Mineral physics and Tomography From the Atomic to the Global Scale (Vol. 117, pp. 133–159). American Geophysical Union.

Lawrence, J. F., & Wysession, M. E. (2006). QLM9: A new radial quality factor (Qμ) model for the lower mantle. Earth and Planetary Science Letters, 241(3–4), 962–971.

Li, Z., Leng, K., Jenkins, J., & Cottaar, S. (2022). Kilometer-scale structure on the core–mantle boundary near Hawaii. Nature Communications, 13(1), 2787.

Liu, C., & Grand, S. P. (2018). Seismic attenuation in the African LLSVP estimated from PcS phases. Earth and Planetary Science Letters, 489, 8–16.

Liu, E., Chapman, M., Varela, I., Li, X., Queen, J. H., & Lynn, H. (2007). Velocity and attenuation anisotropy Implication of seismic fracture characterizations. The Leading Edge, 26(9), 1170–1174.

Liu, J., Li, J., Hrubiak, R., & Smith, J. S. (2016). Origins of ultralow velocity zones through slab-derived metallic melt. Proceedings of the National Academy of Sciences, 113(20), 5547–5551.

Liu, Z., Park, J., & Karato, S. (2016). Seismological detection of low‐velocity anomalies surrounding the mantle transition zone in Japan subduction zone. Geophysical Research Letters, 43(6), 2480–2487.

Mainprice, D. (2015). Seismic anisotropy of the deep Earth from a mineral and rock physics perspective. Treatise of Geophysics, 2. In G. Schubert (Ed.), Treatise of Geophysics (1st ed., Vol. 2, pp. 437–491). Elsevier. 6.00045-6

Matheney, M. P., & Nowack, R. L. (1995). Seismic attenuation values obtained from instantaneous‐frequency matching and spectral ratios. Geophysical Journal International, 123(1), 1–15.

Mavko, G., & Nur, A. (1975). Melt squirt in the asthenosphere. Journal of Geophysical Research (1896-1977), 80(11), 1444–1448.

Muller, G. (1984). Rheological properties and velocity dispersion of a medium with power-law dependence of Q on frequency. Journal of Geophysics, 54(1), 20–29.

Quan, Y., & Harris, J. M. (1997). Seismic attenuation tomography using the frequency shift method. Geophysics, 62(3), 895–905.

Restivo, A., & Helffrich, G. (1999). Teleseismic shear wave splitting measurements in noisyenvironments. Geophysical Journal International, 137(3), 821–830.

Rubino, J. G., & Holliger, K. (2012). Seismic attenuation and velocity dispersion in heterogeneous partially saturated porous rocks. Geophysical Journal International, 188(3), 1088–1102.

Rychert, C. A., Hammond, J. O. S., Harmon, N., Kendall, J. M., Keir, D., Ebinger, C., Bastow, I. D., Ayele, A., Belachew, M., & Stuart, G. (2012). Volcanism in the Afar Rift sustained by decompression melting with minimal plume influence. Nature Geoscience, 5(6), 406–409.

Saha, J. G. (1987). Relationship Between Fourier And Instantaneous Frequency. 1987 SEG Annual Meeting, SEG-1987-0591.

Schlaphorst, D., Silveira, G., Mata, J., Krüger, F., Dahm, T., & Ferreira, A. M. G. (2022). Heterogeneous seismic anisotropy beneath Madeira and Canary archipelagos revealed by local and teleseismic shear wave splitting. Geophysical Journal International, 233(1), 510–528.

Schmandt, B., Jacobsen, S. D., Becker, T. W., Liu, Z., & Dueker, K. G. (2014). Dehydration melting at the top of the lower mantle. Science, 344(6189), 1265–1268.

Shearer, P. M. (2019). Introduction to Seismology. Cambridge University Press.

Silver, P. G., & Chan, W. W. (1988). Implications for continental strucutre and evolution from seismic anisotropy. Nature, 331(6185), 450.

Silver, P. G., & Chan, W. W. (1991). Shear wave splitting and subcontinental mantle deformation. Journal of Geophysical Research, 96(B10), 16429–16454.

Solazzi, S. G., Lissa, S., Rubino, J. G., & Holliger, K. (2021). Squirt flow in partially saturated cracks: a simple analytical model. Geophysical Journal International, 227(1), 680–692.

Sun, Y., Carcione, J. M., & Gurevich, B. (2020). Squirt-flow seismic dispersion models: a comparison. Geophysical Journal International, 222(3), 2068–2082.

Taner, M. T., Koehler, F., & Sheriff, R. E. (1979). Complex seismic trace analysis. Geophysics, 44(6), 1041–1063.

Teanby, N. A., Kendall, J., & Baan, M. V. D. (2004). Automation of Shear-Wave Splitting Measurements using Cluster Analysis. Bulletin of the Seismologial Society of America, 94(2), 453–463.

Thomsen, L. (1995). Elastic anisotropy due to aligned cracks in porous rock. Geophysical Prospecting, 43(6), 805–829.

Tod, S. R. (2001). The effects on seismic waves of interconnected nearly aligned cracks. Geophysical Journal International, 146(1), 249–263.

Uieda, L., Tian, D., Leong, W. J., Schlitzer, W., Grund, M., Jones, M., Fröhlich, Y., Toney, L., Yao, J., Magen, Y., Jing-Hui, T., Materna, K., Belem, A., Newton, T., Anant, A., Ziebarth, M., Quinn, J., & Wessel, P. (2023). PyGMT: A Python interface for the Generic Mapping Tools (v0.9.0) [Computer software]. Zenodo.

Usher, P. J., Kendall, J. ‐M., Kelly, C. M., & Rietbrock, A. (2017). Measuring changes in fracture properties from temporal variations in anisotropic attenuation of microseismic waveforms. Geophysical Prospecting, 65(S1), 347–362.

Verdon, J. P., & Kendall, J.-M. (2011). Detection of multiple fracture sets using observations of shear-wave splitting in microseismic data. Geophysical Prospecting, 59(4), 593–608.

Walker, A. M., & Wookey, J. (2012). MSAT—A new toolkit for the analysis of elastic and seismic anisotropy. Computers & Geosciences, 49, 81–90.

Walsh, E., Arnold, R., & Savage, M. K. (2013). Silver and Chan revisited. Journal of Geophysical Research: Solid Earth, 118(10), 5500–5515.

Wenzlau, F., Altmann, J. B., & Müller, T. M. (2010). Anisotropic dispersion and attenuation due to wave‐induced fluid flow: Quasi‐static finite element modeling in poroelastic solids. Journal of Geophysical Research: Solid Earth, 115(B7).

Werner, U., & Shapiro, S. A. (1999). Frequency-dependent shear-wave splitting in thinly layered media with intrinsic anisotropy. Geophysics, 64(2), 604–608.

Wessel, P., Luis, J. F., Uieda, L., Scharroo, R., Wobbe, F., Smith, W. H. F., & Tian, D. (2019). The Generic Mapping Tools Version 6. Geochemistry, Geophysics, Geosystems, 20(11), 5556–5564.

Whaler, K. A., & Hautot, S. (2006). The electrical resistivity structure of the crust beneath the northern Main Ethiopian Rift. Geological Society, London, Special Publications, 259(1), 293–305.

Wuestefeld, A., Al-Harrasi, O., Verdon, J. P., Wookey, J., & Kendall, J. M. (2010). A strategy for automated analysis of passive microseismic data to image seismic anisotropy and fracture characteristics. Geophysical Prospecting, 58(5), 755–773.

Zhubayev, A., Houben, M. E., Smeulders, D. M. J., & Barnhoorn, A. (2016). Ultrasonic velocity and attenuation anisotropy of shales, Whitby, United Kingdom. Geophysics, 81(1), D45–D56.

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Asplet, J., Wookey, J., Kendall, M., Chapman, M., & Das, R. (2024). Shear-wave attenuation anisotropy: a new constraint on mantle melt near the Main Ethiopian Rift. Seismica, 3(1).




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