George Helffrich

SAC for your MacOS X (or other) system here			Fast, interactive receiver function modelling? Look here...
Focal mechanism drawing? Try here!			Want to listen to the magnitude 9 Boxing Day earthquake and other seismograms (as MP3 files)? Look here...
Focal mechanism animation? Try here!			Browsing for something? Tips and tricks about software and system procedures...
CMT catalog search? Try here!			Want some useful figures? Visit the figure gallery
Calculate travel times? Try here!			Buland and Kennett travel time tables? See here!
Sensible extraction of seismograms from SEED volumes? See here!			Calculate liquid metal seismic wave speeds? See here!

Publication List __________________

• Nakagawa, T., Tsuchiya, T., Satish-Kumar, M., Helffrich, G., eds. Core Mantle Co-Evolution: An Interdisciplinary Approach, AGU Geophysical Monograph Series, v.250, 2023.
• Tagawa, S., Helffrich, G., Hirose, K., Ohishi, Y., High-Pressure Melting Curve of FeH: Implications for Eutectic Melting between Fe and Non-Magnetic FeH, J. Geophys. Res., v.127, doi:10.1029/2022JB024365, 2022.
• Helffrich, G., Hirose, K., Nomura, R., Thermodynamical Modeling of Liquid Fe-Si-Mg-O:Molten Magnesium Silicate Release from the Core, Geophys. Res. Lett., v.47, doi:10.1029/2020GL089218, 2020.
• Helffrich, G., Brasser, R., Shahar, A., The chemical case for Mercury mantle stripping, Prog. Earth Planet. Sci., v.6, 66ff, 2019.
• Helffrich, G., Mainprice, D. Anisotropy at the inner core boundary, Geophys. Res. Lett., v.46, doi:10.1029/2019GL083644, 2019.
• Kusakabe, M., Hirose, K., Sinmyo, R., Kuwayama, Y., Ohishi, Y., Helffrich, G., Melting curve and equation of state of β-Fe₇N₃: Nitrogen in the core?, J. Geophys. Res., v.124, 3448-3457, doi:10.1029/2018JB015823, 2019.
• Helffrich, G. Comment on "Crustal thickness across the Trans-European Suture Zone from ambient noise autocorrelations" by G. Becker and B. Knapmeyer-Endrun, Geophys. J. Int., v.217, 906-908, 2019.
• Helffrich, G. Peer Review's Psychological Potholes, EOS, 94(48), 459, 2018.
• Helffrich, G., Shahar, A., Hirose, K. Isotopic signature of core-derived SiO₂, American Mineralogist, v.103, 1161-1164, 2018.
• Spieker, K., Rondenay, S., Ramalho, R., Thomas, C., Helffrich, G. Constraints on the structure of the crust and lithosphere beneath the Azores Islands from teleseismic receiver functions, Geophys. J. Int. v.213, 824-835, 2018.
• Helffrich, G., Ballmer, M., Hirose, K. Core-exsolved SiO₂ dispersal in the Earth's mantle, J. Geophys. Res. v.123, 176-188, 2018.
• Helffrich, G., Mars core structure -- concise review and anticipated insights from InSight, Prog. Earth Planet. Sci. v.4, 24, 2017.
• Helffrich, G., Feasibility of a magma ocean dynamo on Mars, Prog. Earth Planet. Sci. v.4, 21-26, 2017.
• Helffrich, G., A finite strain approach to thermal expansivity's pressure dependence, American Mineralogist, v.102, 1690-1695, 2017.
• Hirose, K., Morard, G., Sinmyo, R., Umemoto, K., Hernlund, J., Helffrich, G., Labrosse, S., SiO₂ crystallization and compositional evolution of the Earth's core, Nature v.543, 99-102, 2017.
• Ramalho, R.S., Helffrich, G., Madeira, J., Cosca, M., Thomas, C., Quartau, R., Hipolito, A., Rovere, A., Hearty, P.J. and Avila, S.P., Emergence and evolution of Santa Maria Island (Azores) -- The conundrum of uplifted islands revisited, GSA Bulletin, doi: 10.1130/B31538.1, 2016.
• Helffrich, G., Ground Truth: Seismological properties of the core, in Deep Earth: Physics and Chemistry of the Lower Mantle and Core, H. Terasaki, R. Fischer (eds.), AGU Monographs, 113-120 (doi:10.1002/9781118992487), 2016.
• Ramalho, R., Winckler, G. Madeira, J., Helffrich, G., Schaefer, J., Hipólito, A., Quartau, R., Adena, K., Hazard potential of volcanic flank collapses raised by new megatsunami evidence, Science Advances, v.1, E1500456 (doi:10.1126/sciadv.1500456), 2015.
• Thompson, D., Kendall, J.-M., Helffrich, G. R., Bastow, I. D., Wookey, J. W., Snyder, D. B., CAN-HK: An a priori crustal model for the Canadian Shield, Seismological Research Letters, v.86, 1374-1382, 2015.
• Helffrich, G. R., The hard sphere view of the outer core, Earth, Planets, Space, v.67, 73-84, 2015.
• Thompson, D., Hammond, J., Kendall, J.-M., Stuart, G., Helffrich, G., Keir, D., Ayele, A., Goitom, B., Hydrous upwelling across the mantle transition zone beneath the Afar Triple Junction, Geochem., Geophys., Geosyst., v.16, 834-846, 2015.
• Helffrich, G., Outer core compositional layering and constraints on core liquid transport properties, Earth and Planet. Sci. Lett., v. 391, 256-262, 2014.
• Fonseca, J.F.D.B., Chamussa, J.P., Domingues, A.L., Helffrich, G.R., Antunes, E., van Aswegen, G., Pinto, L. V., Custodio, S.I., Manhiça, V. J. MOZART - a seismological investigation of the East African Rift in central Mozambique, Seismological Research Letters, v. 85, p. 108-116, 2014.
• Bina, C., Helffrich, G. R. Geophysical Constraints Upon Mantle Composition, in Treatise on Geochemistry: Geochemistry of the Mantle and Core. Turekian, K. & Holland, H. (eds.), 2nd ed., Elsevier Science, v. 3, 41-65, 2014.
• Helffrich, G. R., John Milne: The maverick founder of modern seismology, Nature, v.504(7479), 216-217, 2013.
• Helffrich, G. R., A Modestly Rewarding Proposal Concerning Peer Review, EOS, v.94(48), 459, 2013.
• Martinez-Arevalo, C., Mancilla, F., Helffrich, G., Garcia, A. Seismic Evidence of a Regional Sublithospheric Low Velocity Layer beneath the Canary Islands, Tectonophysics, v. 608, 586-599, 2013.
• Helffrich, G., Kaneshima, S. Causes and Consequences of Outer Core Stratification, Phys. Earth and Planet. Int., v. 223, 2-7, 2013.
• Kaneshima, S., Helffrich, G. Vp structure of the outermost core derived from analyzing large scale array data of SmKS waves, Geophys. J. Int., v. 93, 1537-1555, 2013.
• Horleston, A., Helffrich, G. Constraining sediment subduction: A converted phase study of the Aleutians and Marianas, Earth and Planet. Sci. Lett., v.359-360, 141-151, 2012.
• Hammond, J., Kendall, J.-M., Collier, J., Helffrich, G. R., Ruempker, G. Plume scar in the mantle lithosphere beneath the Seychelles revealed by seismic imaging Earth and Planet. Sci. Lett., v. 355-356, 20-31, 2012.
• Tonegawa, T., Helffrich, G. R. Basal Reflector under the Philippine Sea Plate, Geophys. J. Int., v. 189, 659-668, 2012.
• Helffrich, G. R. How light element addition can lower core liquid wavespeeds, Geophys. J. Int., v. 188, 1065-1070, 2012.
• Olsson, J. R., Soderlund, U., Hamilton, M. A., Klausen, M. B., Helffrich, G. R. A late Archaean radiating dyke swarm as possible clue to the origin of the Bushveld Complex, Nature Geoscience, v. 4, 865-869, 2011.
• Thompson, D., Helffrich, G., Bastow, I., Kendall, J.-M., Wookey, J., Eaton, D., Snyder, D. Implications of a simple mantle transition zone beneath cratonic North America, Earth Planet. Sci. Lett., v. 312, 28-36, 2011.
• Helffrich, G., J.-M. Kendall, J. O. S. Hammond, and M. R. Carroll, Sulfide melts and long-term low seismic wavespeeds in lithospheric and asthenospheric mantle, Geophys. Res. Lett., 38, L11301, doi:10.1029/2011GL047126, 2011.
• Bastow, I., Thompson, D., Wookey, J., Kendall, J.-M., Helffrich, G., Snyder, D., Eaton, D., Darbyshire, F. Precambrian Crustal Evolution: Seismic Constraints from the Canadian Shield, Geology, v. 39, 91-94, 2011.
• Pawlak, A., Eaton, D., Bastow, I., Kendall, J.-M., Helffrich, G., Wookey, J., Snyder, D. Crustal structure beneath Hudson Bay from ambient-noise tomography: Implications for basin formation, Geophys. J. Int., v. 184, 65-82, 2011.
• Helffrich, G., Kaneshima, S. Outer-core compositional stratification from observed core wave speed profiles Nature, v. 468, 807-810, 2010.
• Kaneshima, S., Helffrich, G. Small scale heterogeneity in the mid-lower mantle beneath the circum-Pacific area Phys. Earth and Planet. Int., v. 183, 91-103, 2010.
• Ramalho, R., Helffrich, G., Cosca, M., Vance, D., Hoffmann, D., Schmidt, D. N. Episodic swell growth inferred from variable uplift of the Cape Verde hotspot islands, Nature Geoscience, v. 3, 774-777, 2010.
• Thompson, D., Bastow, I., Helffrich, G., Kendall, J.-M., Wookey, J., Snyder, D., Eaton, D. Precambrian Crustal Evolution: Seismic Constraints from the Canadian Shield, Earth and Planet. Sci. Lett., v. 297, 655-666, 2010.
• Ramalho, R., Helffrich, G., Cosca, M., Vance, D., Hoffmann, D., Schmidt, D. N. Vertical movements of ocean island volcanoes: insights from a stationary plate Marine Geology, v. 275, 84-95, 2010.
• Helffrich, G., Thompson, D. A stacking approach to estimate Vp/Vs from receiver functions Geophys. J. Int., v. 181, 899-902, 2010.
• Ramalho, R., Helffrich, G., Schmidt, D. N., Vance, D. Tracers of uplift and subsidence in the Cape Verde archipelago J. Geol. Soc. London, v. 167, 519-538, 2010.
• Helffrich, G., Faria, B., Fonseca, J., Lodge, A., Kaneshima, S. Transition zone structure under a stationary hot spot: Cape Verde Earth and Planet. Sci. Lett., v. 289, 156-161, doi 10.1016/j.epsl.2009.11.001, 2010.
• Grevemeyer, I., Helffrich, G., Faria, B., Booth-Rea, G., Schnabel, M., Weinrebe, W. Seismic activity at Cadamosto seamount near Fogo Island, Cape Verdes -- formation of a new ocean island? Geophys. J. Int., v. 180, 552-558, doi 10.1111/j.1365-246X.2009.04440.x, 2010.
• Helffrich, G. Obituary: Paul Silver   Astronomy and Geophysics, v. 50(6), 6.34-6.35, 2009.
• Di Leo, J., Bastow, I., Helffrich, G. Nature of the Moho beneath the Scottish Highlands from a receiver function perspective Tectonophysics, v. 474, 214-222, 2009.
• Helffrich, G., Connolly, J. A. D. Physical contradictions and remedies using simple polythermal equations of state (abstract, reprint) Am. Min., v. 94, 1616-1619, 2009.
• Thomas, C., Kendall, J.-M., Helffrich, G. Probing two low velocity regions with PKP B-caustic amplitudes and scattering Geophys. J. Int., v. 178, 503-512, 2009.
• Kaneshima, S., Helffrich, G. Lower mantle scattering profiles and fabric below Pacific subduction zones Earth and Planet. Sci. Lett., 282, 234-239, 2009.
• Lodge, A., Helffrich, G. Grid-search Inversion of Teleseismic Receiver Functions Geophys. J. Int., v. 178, 513-523, 2009.
• Helffrich, G. Book review: Post-Perovskite: The Last Mantle Phase Transition, K. Hirose, J. Brodholt, T. Lay, D. Yuen, Eds. (2007), (reprint) Am. Min., v. 93, 1947-1948, 2008.
• Helffrich, G. Erratum to Extended-Time Multitaper Frequency Domain Cross-Correlation Receiver-Function Estimation Bull. Seismo. Soc. Am., v. 98, 1608, 2008.
• Wookey, J., Helffrich, G. Inner-core shear-wave anisotropy and texture from an observation of PKJKP waves Nature, v. 454, 873-877, 2008.
• Brodholt, J., Helffrich, G., Trampert, J. Chemical versus thermal heterogeneity in the lower mantle: the most likely role of anelasticity Earth and Planet. Sci. Lett., v. 262, 429-437, 2007.
• Bastow, I., Owens, T. J., Helffrich, G., Knapp, J. H. Spatial and temporal constraints on sources of seismic anisotropy: Evidence from the Scottish Highlands (reprint) Geophys. Res. Lett., v. 34, doi:10.1029/2006GL028911, 2007.
• Helffrich, G., Heleno, S.I.N., Faria, B., Fonseca, J.F.B.D. Hydroacoustic detection of volcanic ocean-island earthquakes, Geophys. J. Int., v. 167, 1529-1536, 2006.
• Lodge, A., Helffrich, G. Depleted swell root beneath the Cape Verde Islands Geology, v. 34, 449-452, 2006.
• Helffrich, G. Heterogeneity in the mantle--its creation, evolution and destruction (reprint) Tectonophysics, v. 416, 23-31, 2006.
• Restivo, A., Helffrich, G. Core-mantle boundary structure investigated using SKS and SKKS polarization anomalies (reprint) Geophys. J. Int., v. 165, 288-302, doi: 10.1111/j.1365-246X.2006.02901, 2006.
• Helffrich, G. Extended-time multi-taper frequency domain cross-correlation receiver function estimation (preprint) Bull. Seismo. Soc. Am., v. 96, 344-347, 2006.
• Helffrich, G. and Kaneshima, S. Seismological Constraints on Core Composition from Fe-O-S Liquid Immiscibility(abstract) Science, v. 306, 2239-2242, 2004.
• Brana, L. and Helffrich, G. A scattering region near the core-mantle boundary under the North Atlantic. Geophys. J. Int. v. 158, 625-636, 2004 (submitted, 2002!).
• Helffrich, G. Basic principles of electromagnetic and seismological investigation of shallow subduction zone structure. Inside the Subduction Factory, AGU Geophys. Mon. v. 138, 47-57, 2003.
• Helffrich, G., Asencio, E., Knapp, J. and Owens, T. J. Transition zone structure in a tectonically inactive area: 410 and 660 km discontinuity properties under the northern North Sea. Geophys. J. Int., v. 155, 193-199, 2003.
• Kaneshima, S. and Helffrich, G. Subparallel dipping heterogeneities in the mid-lower mantle. J. Geophys. Res. v. 108(B5), 2272, 10.1029/2001JB001596, 2003.
• Asencio, E., Knapp, J. H., Owens, T. J. and Helffrich, G. Mapping fine-scale heterogeneities within the continental mantle lithosphere beneath Scotland: Combining active- and passive-source seismology. Geology, v. 31(6), 477-480, 2003.
• Helffrich, G. Chemical and seismological constraints on mantle heterogeneity. Phil. Trans. of the Royal Society (Mathematical, Physical & Engineering Sciences), v. 360, 2493-2506, 2002.
• Helffrich, G. Thermal variations in the mantle inferred from 660-km discontinuity topography and tomographic wavespeed variations (preprint), Geophys. J. Int., v. 151, 935-943, 2002.
• Helffrich, G., Kaneshima, S., and Kendall, J.-M. A local, crossing-path study of attenuation and anisotropy of the inner core (preprint), Geophys. Res. Lett., 10.1029/2001GL014059, 2002.
• Collier, J. and Helffrich. G. Estimate of inner core rotation rate from United Kingdom regional seismic network data and consequences for inner core dynamical behaviour (preprint), Earth and Planet. Sci. Lett., v. 193, 523-537, 2002.
• Helffrich. G., Wiens, D. A., Vera, E., Barrientos, S., Shore, P., Robertson, S. and Adaros, R. A teleseismic shear-wave splitting study to investigate mantle flow around South America and implications for plate-driving forces, (reprint), Geophys. J. Int., v. 149, F1-F7, 2002.
• Collier, J., Helffrich, G., and Wood, B. Seismic discontinuities and subduction zones (reprint), Phys. Earth and Planet. Int., v. 127, 35-49, 2001.
• Helffrich, G. and Wood, B. The Earth's Mantle, Nature, v. 412, 501-507,2001.
• Kendall, J.-M. and Helffrich, G. SPICeD: imaging the deep Earth, Astronomy and Geophysics, v. 42, 3.26-3.29, 2001.
• Collier, J. and Helffrich. G. The thermal influence of the subducting slab beneath South America from 410 and 660 km discontinuity observations, Geophys. J. Int., v. 147, 319-329, 2001.
• Helffrich, G. Topography of the transition zone seismic discontinuities Rev. Geophys., v. 38(1), 141-158, 2000.
• Restivo, A., Helffrich, G. Teleseismic shear-wave splitting measurement in noisy environments, Geophys. J. Int., v.137, 821-830, 1999.
• Helffrich, G. Practical use of Suzuki's thermal expansivity formulation Phys. Earth and Planet. Int., v. 116, 133-136, 1999.
• Kaneshima, S., Helffrich, G. Dipping low-velocity layer in the mid-lower mantle: Evidence for geochemical heterogeneity Science, v. 283, 1888-1891, 1999.
• Helffrich, G. Comment on ``Seismological evidence for the existence of anisotropic zone in the metastable wedge inside the subducting Izu-Bonin slab'' by Takashi Iidaka and Kazushige Obara, Geophys. Res. Lett., v. 25, 3243-3244, 1998.
• Kaneshima, S., Helffrich, G. Detection of lower mantle scatterers northeast of the Mariana subduction zone using short-period array data, J. Geophys. Res., v. 103, 4825-4838, 1998.
• Helffrich, G. How good are routinely determined focal mechanisms? Empirical statistics based on a comparison of Harvard, USGS and ERI moment tensors, Geophys. J. Int., v. 131, 741-750, 1997.
• Barruol, G., Helffrich, G. Shear wave splitting around the northern Atlantic: Frozen Pangaean lithospheric anisotropy? (reprint), Tectonophysics, v. 279, 135-148, 1997.
• Helffrich, G., Abers G. Slab Low-Velocity Layer in the Eastern Aleutian Subduction Zone, Geophys. J. Int., v.130, 640-648, 1997.
• Collier, J., Helffrich, G. Topography of the "410" and "660" km seismic discontinuities in the Izu-Bonin subduction zone, Geophys. Res. Lett., v.24, 1535-1538, 1997.
• Helffrich, G. GEBCO Digital Atlas (review), Terra Nova, v.8, 659-661, 1996.
• Helffrich, G., Wood, B. 410 km discontinuity sharpness and the form of the olivine - phase diagram: Resolution of apparent seismic contradictions, Geophys. J. Int., v.126, F7-F12, 1996.
• Helffrich, G. Subducted lithospheric slab velocity structure: Observations and mineralogical inferences, in Subduction Top to Bottom, Bebout, G., Scholl, D., Kirby, S., and Platt, J. eds., AGU Geophys. Mon. 96, 215-222, 1996.
• Helffrich, G., Lithospheric deformation inferred from teleseismic shear wave splitting observations in the UK (reprint), J. Geophys. Res., v.100, 18195-18204, 1995.
• Helffrich, G., Bina, C. Frequency dependence of the visibility and depths of mantle seismic discontinuities, Geophys. Res. Lett., v.21, 2613-2616, 1994.
• Bina, C.R., Helffrich, G.R. Phase transition clapeyron slopes and transition zone seismic discontinuity topography, J. Geophys. Res., v.99(B8), 15853-15860, 1994.
• Helffrich, G., Silver, P., Given, H. Shear wave splitting variation over short spatial scales on continents, Geophys. J. Int., v.119(2), 561-573, 1994.
• Helffrich, G., Sacks, S. Scatter in differential PKP travel times and implications for mantle and core phenomena, Geophys. Res. Lett., v.21, 2167-2170, 1994.
• Helffrich, G., Stein, S. Study of the structure of the slab-mantle interface using reflected and converted seismic waves, Geophys. J. Int., v.115, 14-40, 1993.
• Bina, C.R., Helffrich, G.R. Calculation of elastic properties from thermodynamic equation of state principles, Ann. Reviews of Earth Planet. Sci., v.20, 527-552, 1992.
• Helffrich, G., Brodholt, J. The relationship of deep seismicity to the thermal age of subducted lithosphere, Nature, v.353, 252-255, 1991.
• Helffrich, G.R., Stein, S., Wood, B.J. Subduction zone thermal structure and mineralogy and their relationship to seismic wave reflections and conversions at the slab/mantle interface, J. Geophys. Res., v.94(B1), 753-763, 1989.
• Helffrich, G.R., Wood, B.J. The subregular model for multicomponent solutions, American Mineralogist, v.74, 1016-1022, 1989.
• Sharp, Z.D., Helffrich, G.R., Bohlen, S.R., Essene, E.J. The stability of sodalite and phase equilibria in the system NaAlSiO4 - NaCl, Geochimica et Cosmochimica Acta, v.53, 1943-1954, 1989.