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3-D crustal structure using seismic waves P and S ( SimulpPS )

CNRST – MARWAN Morocco. 3-D crustal structure using seismic waves P and S ( SimulpPS ). Youssef Timoulali CNRST. timoulali@cnrst.ma. EUMEDGRID-Support / CHAIN/ EPIKH Workshop Rabat 16 June 2011 . Types of Seismic Waves.

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3-D crustal structure using seismic waves P and S ( SimulpPS )

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  1. CNRST – MARWAN Morocco 3-D crustal structure usingseismicwaves P and S (SimulpPS) Youssef Timoulali CNRST timoulali@cnrst.ma EUMEDGRID-Support / CHAIN/ EPIKH Workshop Rabat 16 June 2011

  2. Types of Seismic Waves There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves. . body waves P wave or primary wave (compressional waves) S wave or secondary wave ,

  3. Seismicwavemodelisationfrom source to seismic station The body wave travel time T from an earthquake i to a seismic station j is expressed using ray theory as a path integral (2) (1) Where u is the slowness field ds is an element of path length (u=1/V où V vitesse locale) τi : origin time  tij : arrived time (from station)

  4. Model parameters Receiver (Location) Observed and arrived times The source coordinates (x1,x2,x3) Origin times Ray path Slowness field Only known Unknown (Model parameters) The arrivaltime tijobs are mesuredat a station of network The calculatedarrival times tij cal are determinedfromequation (1) and (2) using trial hypocenters, origin times and an initial model of the seismicvelocity Structure ( the priori information).

  5. The misfit between observed and predicted (calculated) arrival times are the residuals rij rij = tijobs –tij cal rijpositif Lowvelocity rijnegatifhighvelocity The residualcanberelated to desired perturbations to the Hypocenterand velocitystructure parameters by linear approximation (3)

  6. Goal of local earthquaketomography Tomo= section Graphy = image * To improve the estimation of model parameters (structure and hypocenters) by perturbingthem. * The perturbation isused to minimizesomemeasure of misfit data. * This generallyrequire an iterativescheme for solution..

  7. Methodology Computaion of travel time and ray path It is essential to computetravel time and ray path in a heterogeneous earth model quicly and accurately. Twoapproximatelytracing techniques developped by thurberworks wellwhenepicentral distance are shorterthan 50km: ART : Approxiate Ray Tracing (Thurber 1983) CHT : Pseudo-bendingmethod, designed to perturb an ART path closer to the true ray path.

  8. Approximate Ray tracing (ART) Adopt a brut force approach to finding the minimum time ray path. A large set of smoothcurvesconnecting the soucre and receiver are constructedusing an efficient but somewhatarbitraryscheme The travel time alongeachcurveiscalculatednumerically, The estimatedtruepathobtained by computedtravel times ispresneted by « fastest » curve.

  9. The pseudo-bending (CHT) method Takes a geometricapproach to estimation of the true ray path. This permits a given ray pathestimate to have a curvaturewhich varies along the ray, as well as allowing the path to deviatefrom a single plan.

  10. Inverse problem * Optimisation to found the cruste structure * The inversion alow to construct the neartrue structure from physique data

  11. Grid computation Job.JDL Type = "Job"; JobType = "Normal"; Executable = "simulps.exe"; StdOutput = "simul.out"; StdError = "simul.err"; InputSandbox = {"simulps.exe","CNTL","EQKS","MOD","STNS"}; OutputSandbox = {"simul.err","output","nodes.out","resol.out","f24", "velomod.out","hypo71list","f28","itersum"}; Arguments = "-f"; ShallowRetryCount = 3; #Requirements = other.GlueCEUniqueId == "ce1.cnrst.magrid.ma:8443/cream-pbs-eumed"

  12. 3-D computation result West AlboranSeacrust structure Total earthquake = 5972 Observation total =110176 P obs = 58774, S obs = 51402 PC/Windows Computation beganat 14:47:01 Computation finishedat 17:43:37 Linux/ Grid Computation beganat 13-Jun-11 14:01:19 Computation finishedat 13-Jun-11 14:33:33

  13. Crustvelocity Crustvelocity perturbation Profile along longitude 5°W

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