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The 2011 Lorca earthquake slip distribution controlled by groundwater crustal unloading


Earthquake initiation, propagation and arrest are influenced by fault frictional properties1,2 and preseismic stress3,4. Studies of triggered and induced seismicity5,6,7 can provide unique insights into this influence. However, measurements of near-field, surface ground deformation8,9 and pre-earthquake stress conditions necessary for such studies are rare. Here, we use geodetic data to determine surface deformation associated with the Mw 5.1 earthquake that occurred in Lorca, southeast Spain, on 11 May 2011. We use an elastic dislocation model to show that earthquake nucleation and the area of main fault slip occurred at very shallow depths of 2–4 km, on a rupture plane along the Alhama de Murcia Fault. Slip extended towards the surface, across fault segments with frictional properties that changed from unstable to stable. The area of fault slip correlates well with the pattern of positive Coulomb stress change that we calculate to result from the extraction of groundwater in a nearby basin aquifer. We therefore suggest that the distribution of shallow slip during the Lorca earthquake could be controlled by crustal unloading stresses at the upper frictional transition of the seismogenic layer, induced by groundwater extraction. Our results imply that anthropogenic activities could influence how and when earthquakes occur.

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Figure 1: Location and kinematics of the Lorca earthquake.
Figure 2: Ground deformation data and model.
Figure 3: Fault slip and unloading stress change models.


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Our research was financially supported by an Ontario Early Researcher Award, the CSRN NSERC Strategic Network Grant, and the NSERC and Aon Benfield/ICLR IRC in Earthquake Hazard Assessment. P.J.G. also acknowledges the Banting Postdoctoral Fellowship of the Government of Canada. Further support was provided by the projects CGL2005-05500-C02, CGL2008-06426-C01-01/BTE, PCI2006-A7-0660 and AYA2010-17448; as well the Moncloa International Campus of Excellence. Radar data were from ESA CAT1:4460 and 6745 projects. GPS data were from Meristemum, Red Activa de Murcia and IGN networks. GMT software was used to create all figures. We are grateful to J-P. Avoua for helpful comments. We thank P. Bhattacharya, N. Cho and F. Lorenzo-Martı´n for stimulating discussions, F. Luzón, and J. Morales and A. Concha for sharing manuscripts before publication13,17.

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P.J.G. carried out the radar data analysis; dislocation, loading and pore-pressure diffusion models; and wrote the manuscript with the help of all co-authors. K.F.T. and P.J.G. carried out the CFF models. M.P. processed daily GPS data and computed the two-dimensional strain-rate tensor. F.C. processed high-rate GPS data and analysed accelerometer frequency spectra. J.F. and P.J.G. designed the research.

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Correspondence to Pablo J. González.

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González, P., Tiampo, K., Palano, M. et al. The 2011 Lorca earthquake slip distribution controlled by groundwater crustal unloading. Nature Geosci 5, 821–825 (2012).

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