The speed at which an earthquake rupture propagates affects its energy balance and ground shaking impact. Dynamic models of supershear earthquakes, which are faster than the speed of shear waves, often start at subshear speed and later run faster than Eshelby’s speed. Here we present robust evidence of an early and persistent supershear rupture at the sub-Eshelby speed of the 2018 magnitude 7.5 Palu, Indonesia, earthquake. Slowness-enhanced back-projection of teleseismic data provides a sharp image of the rupture process, along a path consistent with the surface rupture trace inferred by subpixel correlation of synthetic-aperture radar and satellite optical images. The rupture propagated at a sustained velocity of 4.1 km s–1 from its initiation to its end, despite large fault bends. The persistent supershear speed is further validated by seismological evidence of far-field Rayleigh Mach waves. The unusual features of this earthquake probe the connections between the rupture dynamics and fault structure. An early supershear transition could be promoted by fault roughness near the hypocentre. Steady rupture propagation at a speed unexpected in homogeneous media could result from the presence of a low-velocity damaged fault zone.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $15.58 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The ALOS-2 original data can be obtained from JAXA. Derived pixel offset maps can be obtained from the authors. Copernicus Sentinel images are available at no cost from the Copernicus Open Access Hub (https://scihub.copernicus.eu/). PlanetScope images are available from Planet Labs (https://www.planet.com/). The broadband seismograms are accessed from IRIS (www.iris.edu) data centres for the Australian and Alaskan networks, from ORFEUS (www.orfeus-eu.org) for the Turkish network, from GEONET (www.geonet.org.nz) for the New Zealand network and from Hi-net (http://www.hinet.bosai.go.jp) for the Japan network. The earthquake catalogues are obtained from the USGS NEIC (http://earthquake.usgs.gov). The background topography and bathymetry used in our figures are provided by the NOAA National Center for Environmental Information (https://www.ngdc.noaa.gov/mgg/global/etopo1sources.html). The USGS W-phase solution can be accessed at https://earthquake.usgs.gov/earthquakes/eventpage/us1000h3p4/moment-tensor. The computer code for back-projection is available upon request to L.M.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Burridge, R. Admissible speeds for plane‐strain self‐similar shear cracks with friction but lacking cohesion. Geophys. J. R. Astronom. Soc. 35, 439–455 (1973).
Andrews, D. J. Rupture velocity of plane strain shear cracks. J. Geophys. Res. 81, 5679–5687 (1976).
Xia, K., Rosakis, A. J. & Kanamori, H. Laboratory earthquakes: the sub-Rayleigh-to-supershear rupture transition. Science 303, 1859–1861 (2004).
Das, S. in Perspectives on European Earthquake Engineering and Seismology Vol. 2 (ed. Ansall, A.) 1–20 (Springer, Cham, 2015).
Bouchon, M. et al. Faulting characteristics of supershear earthquakes. Tectonophysics 493, 244–253 (2010).
Huang, Y., Ampuero, J. P. & Helmberger, D. V. The potential for supershear earthquakes in damaged fault zones—theory and observations. Earth Planet. Sci. Lett. 433, 109–115 (2016).
Perrin, C., Manighetti, I., Ampuero, J. P., Cappa, F. & Gaudemer, Y. Location of largest earthquake slip and fast rupture controlled by along‐strike change in fault structural maturity due to fault growth. J. Geophys. Res. Solid Earth 121, 3666–3685 (2016).
Bruhat, L., Fang, Z. & Dunham, E. M. Rupture complexity and the supershear transition on rough faults. J. Geophys. Res. Solid Earth 121, 210–224 (2016).
Socquet, A. et al. India and Sunda plates motion and deformation along their boundary in Myanmar determined by GPS. J. Geophys. Res. Solid Earth 111, B05406 (2006).
Watkinson, I. M. & Hall, R. in Geohazards in Indonesia: Earth Science for Disaster Risk Reduction (eds Cummins, P. R. & Meilano, I.) 71–120 (Geological Society Special Publications Vol. 441, Geological Society, London, 2017).
Cipta, A et al. in Geohazards in Indonesia: Earth Science for Disaster Risk Reduction (eds Cummins, P. R. & Meilano, I.) 133–152 (Geological Society Special Publications Vol. 441, Geological Society, London, 2017).
Kiser, E. & Ishii, M. Back-projection imaging of earthquakes. Annu. Rev. Earth Planet. Sci. 45, 271–299 (2017).
Meng, L., Zhang, A. & Yagi, Y. Improving back projection imaging with a novel physics‐based aftershock calibration approach: A case study of the 2015 Gorkha earthquake. Geophys. Res. Lett. 43, 628–636 (2016).
Meng, L., Inbal, A. & Ampuero, J. P. A window into the complexity of the dynamic rupture of the 2011 M w 9 Tohoku‐Oki earthquake. Geophys. Res. Lett. 38, L00G07 (2011).
Meng, L. et al. Earthquake in a maze: compressional rupture branching during the 2012 M w 8.6 Sumatra earthquake. Science 337, 724–726 (2012).
Laske, G., Masters, G., Ma, Z. & Pasyanos, M. Update on CRUST1. 0—a 1-degree global model of Earth’s crust. Geophys. Res. Abstr. 15, 2658 (2013).
Fialko, Y., Sandwell, D., Simons, M. & Rosen, P. Three-dimensional deformation caused by the Bam, Iran, earthquake and the origin of shallow slip deficit. Nature 435, 295–299 (2005).
Xu, X. et al. Refining the shallow slip deficit. Geophys. J. Int. 204, 1867–1886 (2016).
Vallée, M., Landès, M., Shapiro, N. M. & Klinger, Y. The 14 November 2001 Kokoxili (Tibet) earthquake: high‐frequency seismic radiation originating from the transitions between sub‐Rayleigh and supershear rupture velocity regimes. J. Geophys. Res. Solid Earth 113, B07305 (2008).
Wang, D., Mori, J. & Koketsu, K. Fast rupture propagation for large strike-slip earthquakes. Earth. Planet. Sci. Lett. 440, 115–126 (2016).
Huang, Y., Ampuero, J. P. & Helmberger, D. V. Earthquake ruptures modulated by waves in damaged fault zones. J. Geophys. Res. Solid Earth 119, 3133–3154 (2014).
Vallée, M. & Dunham, E. M. Observation of far‐field Mach waves generated by the 2001 Kokoxili supershear earthquake. Geophys. Res. Lett 39, L05311 (2012).
Dunham, E. M. & Bhat, H. S. Attenuation of radiated ground motion and stresses from three-dimensional supershear ruptures. J. Geophys. Res. Solid Earth 113, B08319 (2008).
Ekström, G. A global model of Love and Rayleigh surface wave dispersion and anisotropy, 25-250 s. Geophys. J. Int. 187, 1668–1686 (2011).
Dunham, E. M. Conditions governing the occurrence of supershear ruptures under slip‐weakening friction. J. Geophys. Res. Solid Earth 112, B07302 (2007).
Liu, Y. & Lapusta, N. Transition of model II cracks from sub-Rayleigh to intersonic speeds in the presence of favorable heterogeneity. J. Mech. Phys. Solids 56, 25–50 (2008).
Dieterich, J. H. & Smith, D. E. in Mechanics, Structure and Evolution of Fault Zones (eds Ben-Zion, Y. & Sammis, C.) 1799–1815 (Birkhäuser, Basel, 2009).
Burridge, R., Conn, G. & Freund, L. B. The stability of a rapid mode II shear crack with finite cohesive traction. J. Geophys. Res. 85, 2210–2222 (1979).
Rosakis, A. J., Samudrala, O. & Coker, C. Cracks faster than the shear wave speed. Science 284, 1337–1340 (1999).
Thomas, M. Y. & Bhat, H. S. Dynamic evolution of off-fault medium during an earthquake: a micromechanics based model. Geophys. J. Int. 214, 1267–1280 (2018).
Gabriel, A. A., Ampuero, J. P., Dalguer, L. A. & Mai, P. M. Source properties of dynamic rupture pulses with off‐fault plasticity. J. Geophys. Res. Solid Earth 118, 4117–4126 (2013).
Pathier, E. et al. Displacement field and slip distribution of the 2005 Kashmir earthquake from SAR imagery. Geophys. Res. Lett. 33, L20310 (2006).
Rosen, P. A., Gurrola, E., Sacco, G. F. & Zebker, H. in EUSAR 2012: 9th European Conference on Synthetic Aperture Radar 730–733 (IEEE, 2012).
Liang, C. & Fielding, E. J. Interferometry with ALOS-2 full-aperture ScanSAR data. IEEE Trans. Geosci. Remote Sens. 55, 2739–2750 (2017).
Planet Team Planet Application Program Interface: In Space for Life on Earth (Planet, San Francisco, 2017).
Debella-Gilo, M. & Kääb, A. Sub-pixel precision image matching for measuring surface displacements on mass movements using normalized cross-correlation. Remote Sens. Environ. 115, 130–142 (2011).
Leprince, S., Ayoub, F., Klinger, Y. & Avouac, J. P. in Geoscience and Remote Sensing Symposium 2007 1943–1946 (IEEE, 2007).
Ishii, M., Shearer, P. M., Houston, H. & Vidale, J. E. Extent, duration and speed of the 2004 Sumatra-Andaman earthquake imaged by the Hi-Net array. Nature 435, 933–936 (2005).
Ishii, M., Shearer, P. M., Houston, H. & Vidale, J. E. Teleseismic P wave imaging of the 26 December 2004 Sumatra‐Andaman and 28 March 2005 Sumatra earthquake ruptures using the Hi‐net array. J. Geophys. Res. Solid Earth 112, B11307 (2007).
Fan, W. & Shearer, P. M. Investigation of backprojection uncertainties with M 6 earthquakes. J. Geophys. Res. Solid Earth 122, 7966–7986 (2017).
Meng, L. et al. Double pincer movement: encircling rupture splitting during the 2015 M w 8.3 Illapel earthquake. Earth Planet. Sci. Lett. 495, 164–173 (2018).
Avouac, J. P. et al. The 2013, M w 7.7 Balochistan earthquake, energetic strike-slip reactivation of a thrust fault. Earth Planet. Sci. Lett. 391, 128–134 (2014).
Meng, L., Allen, R. M. & Ampuero, J. P. Application of seismic array processing to earthquake early warning. Bull. Seismol. Soc. Am. 104, 2553–2561 (2014).
An, C. & Meng, L. Application of array backprojection to tsunami prediction and early warning. Geophys. Res. Lett. 43, 3677–3685 (2016).
Feng, T. & Meng, L. A high-frequency distance metric in ground-motion prediction equations based on seismic array back-projections. Geophys. Res. Lett. 45, 11612–11621 (2018).
H.B. and L.M. were supported by NSF Earthscope grant no. EAR-1614609, NSF Geophysics grant no. EAR-1723192, and by the Leon and Joanne V.C. Knopoff Foundation. J.-P.A. acknowledges funding from the UCA-JEDI Investments in the Future project managed by the French National Research Agency (ANR, grant no. ANR-15-IDEX-01) and from ANR grant no. ANR-17-CE31-0008-01. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA) for the Earth Surface and Interior focus area and NISAR Science Team. The ALOS-2 original data are copyright JAXA and provided under JAXA ALOS RA6 PI projects P3278 and P3360. Sentinel-2 images used in our analysis contain modified Copernicus Sentinel data (2018), processed by the European Space Agency. We thank Planet Labs for access to their PlanetScope imagery. Funding for C.W.D.M. was provided under a NASA Postdoctoral Program fellowship administered by the Universities Space and Research Association through a contract with NASA. H.B. acknowledges that the Python software package ObSpy was used for data requesting, waveform filtering and cross-correlations.
Supplementary Figures, Supplementary Tables, Supplementary Text
About this article
Nature Geoscience (2019)
Nature Geoscience (2019)
Pure and Applied Geophysics (2019)
Coseismic landslides triggered by the 2018 Hokkaido, Japan (Mw 6.6), earthquake: spatial distribution, controlling factors, and possible failure mechanism