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TABOO: The Alto Tiberina Near Fault Observatory

A 3-D velocity model for earthquake location from combined geological and geophysical data: a case study from the TABOO Near Fault Observatory (Northern Apennines, Italy).

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TABOO: The Alto Tiberina Near Fault Observatory

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  1. A 3-D velocity model for earthquake location from combined geological and geophysical data: a case study from the TABOO Near Fault Observatory (Northern Apennines, Italy) D. Latorre 1, A. Lupattelli 2, F. Mirabella 2, F. Trippetta 3, L. Valoroso 1, A. Lomax 4, R. Di Stefano 1, C. Collettini 3, L. Chiaraluce 1 Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy Università degli Studi di Perugia, Italy Università La Sapienza, Rome, Italy Alomax Scientific, Mouans-Sartoux, France

  2. TABOO: The Alto Tiberina Near Fault Observatory SW NE The TABOO seismic network ~ 60 seismic stations (surface and shallow boreholes) ~39,000 earthquakes in 4 years (2010-2014) ML 3.7 05-2010 ML 4.1 12-2013

  3. COMBINING GEOLOGICAL AND GEOPHYSICAL DATA Seismic reflection profiles Geological surveys 3D velocity model In situ velocity measurements Laboratory measurements Local earthquake recordings

  4. INTEGRATING SURFACE AND SUBSURFACE DATA • DATA • 40 seismic reflection profiles • (~300 km, 4s twt) and • 6 deep borheoles (5 km depth) • Detailed geological maps • - Structural surveys data 3D Geological Model Mirabella et al., Tectonics 2011 3D layered Model • 5 layers = lithostratigraphic units: • similar rock types • similar seismic velocities - Turbidites Cenozoic Carbonates Triassic Evaporites Acoustic basement Crystalline Basement

  5. DIRECT P AND S VELOCITY MEASUREMENTS Laboratory Boreholes Velocity model VP1, VS1 Turbidites VP2, VS2 Carbonates Evaporites VP3, VS3 Acoustic basement P-wave velocity (m/s) VP4, VS4 VP5, VS5 Crystalline basement In situ VP measurements (sonic logs) Lab measurements of VP and VS (dry condition) • Proper scale (in situ) • In situ conditions (in situ) • Seismic frequency (in situ) • Good control on the Boundary conditions (lab) • Detailed measurements for the different layers (lab) • S-velocity measurements (lab)

  6. EARTHQUAKE DATA About 39,000 earthquakes have been analyzed in quasi real time with an automatic procedure (Valoroso et al., Poster section, EGU2014-5486) • Our dataset selection • P and S picking weights ≤ 1 • At least 10 P and 8 S pickings for event • 5982 events • about 80,000 P and 40,000 S pickings

  7. 3D VELOCITY MODEL CONSTRUCTION From direct velocity measurements (boreholes and laboratory) From the 3D geological model (seismic reflection profiles, boreholes and geological surveys) VP1, VS1 VP2, VS2 VP3, VS3 VP4, VS4 Average velocities of P and S waves for each layer VP5, VS5 Geometry of the velocity layers 3D velocity model Model validation Earthquake hypocenter location of the selected dataset with the NonLinLoc code (alomax.free.fr/nlloc)

  8. 3D VERSUS 1D VELOCITY MODEL 1D velocity models of the Alto Tiberina Fault area Carannante et al., in prep. - Velest + regional model Chiaraluce et al., 2007 - Borehole data/geology Piccinini et al., 2003 - Velest Models 1,2,3,4 - Genetic alghoritm+NLLoc 3 4 1 2

  9. 3D VERSUS 1D VELOCITY MODEL RMS 3D model 1D model

  10. 3D VERSUS 1D VELOCITY MODEL PDF VOLUME 3D model 1D model The PDF shape depends on the model complexity PDF = Probability Density Function Lomax et al., 2009

  11. 3D VERSUS 1D VELOCITY MODEL SW NE carbonates evaporites 1 ac basement ATF crystalline basement SW NE 1 ATF

  12. 3D VERSUS 1D VELOCITY MODEL SW NE carbonates evaporites ac basement ATF 2 crystalline basement SW NE ATF 2

  13. CONCLUSIONS • By combining different data we have provided a 3D P- and S-wave velocity model allowing for: • 1) Accurate earthquake locations • P- and S- wave arrival time residuals in comparison to previous 1D velocity models • The consistency of the earthquake distribution with known geological structures. • An optimal reference model for future (3 and 4D) tomographic inversions

  14. NEXT STEP: INVERSION SCHEME FROM DIRECT VELOCITY MEASUREMENTS FROM LOCAL EARTHQUAKE DATA FROM THE 3D GEOLOGICAL MODEL Geometry of the velocity layers (fixed) Velocity ranges of P and S waves for each layer Selected P and S first arrival times from the TABOO dataset Generation of P- and S- velocity models Earthquake hypocenter location (NonLinLoc alghoritm) Genetic alghoritm WORK IN PROGRESS misfit

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