The 2011 Lorca earthquake slip distribution controlled by groundwater crustal unloading

Journal name:
Nature Geoscience
Volume:
5,
Pages:
821–825
Year published:
DOI:
doi:10.1038/ngeo1610
Received
Accepted
Published online

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.

At a glance

Figures

  1. Location and kinematics of the Lorca earthquake.
    Figure 1: Location and kinematics of the Lorca earthquake.

    a, Southwest Spain seismicity (2000–2010), focal mechanisms (1970–2010), long-term GPS velocity (2006–2011, grey) and coseismic vectors (red). Major mapped faults are labelled. b, Lorca city and Alto Guadalentin Basin. IGN mainshock focal mechanisms (black), pre-shock (light grey) and largest aftershock (dark grey), and relocated seismic sequence13. The black stars are damage locations; the red lines are faults11. The contour lines indicate 2cmyr−1 InSAR subsidence due to groundwater pumping14. Blue rectangle: fault surface projection. AMF, Alhama de Murcia Fault. c, Groundwater depth evolution from different data sources (see Supplementary Information). d, InSAR (triangles) and line-of-sight (LOS)-projected GPS ground-surface subsidence at LORC station.

  2. Ground deformation data and model.
    Figure 2: Ground deformation data and model.

    ad, Descending LOS displacement maps and LORC station horizontal GPS vector (a and c) and distributed slip model predictions (b and d). a,b, Data and model for track 008 (20110426–20110526). c,d, Data and model for track 209 (20110510–20110609). The insets in a and c indicate LOS angle, positive values away from the satellite. Blue rectangle: fault surface projection. Dashed lines are profile locations (ad). e,f, Observed and simulated data along two profiles, and local topography. 2σ data profiles based on standard deviation in a 1-km-wide area normal to the profile direction.

  3. Fault slip and unloading stress change models.
    Figure 3: Fault slip and unloading stress change models.

    a, Coseismic distributed fault slip model. b, Fifty years (~ 1960–2010) of cumulative ΔCFF (slip rake=36°) resolved on the rupture fault plane by crustal unloading. c,d, Fault dip profiles ~ 2.5km north of the city (c) and in Lorca (d) for the coseismic slip, and three cumulative unloading ΔCFF models with variable slip rake (thrusting,blue; left-lateral, green; oblique, red with rake=36°). The background of c shows the depth percentage of the long-term crustal seismicity (2000–2010) located (www.ign.es) in southwest Spain, under a similar compressive regime, used to infer the depth of the upper frictional transition limit.

References

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Affiliations

  1. Department of Earth Sciences, University of Western Ontario, Biological and Geological Sciences Building, London, Ontario N6A 5B7, Canada

    • Pablo J. González &
    • Kristy F. Tiampo
  2. Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo—Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy

    • Mimmo Palano &
    • Flavio Cannavó
  3. Instituto de Geociencias (CSIC-UCM), Facultad de Ciencias Matemáticas, Plaza de Ciencias 3, Ciudad Universitaria, 28040 Madrid, Spain

    • José Fernández

Contributions

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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The authors declare no competing financial interests.

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