Examples Using both 2-D sections from Figure 3, data has been modeled for (acoustic) P and (elastic) S wave field

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1 Suslt illumintion studies through longitudinl nd trnsversl wve propgtion Riz Ali *, Jn Thorecke nd Eric Verschuur, Delft University of Technology, The Netherlnds Copyright 2007, SBGf - Sociedde Brsileir de Geofísic This pper ws prepred for presenttion t the 10 th Interntionl Congress of The Brzilin Geophysicl Society held in Rio de Jneiro, Brzil, Novemer Contents of this pper were reviewed y the Technicl Committee of the 10 th Interntionl Congress of the Brzilin Geophysicl Society nd do not necessrily represent ny position of the SBGf, its officers or memers. Electronic reproduction, or storge of ny prt of this pper for commercil purposes without the written consent of the Brzilin Geophysicl Society is prohiited. Astrct In this pper, propgtion nd illumintion studies hve een performed for coustic nd elstic wve field propgtion through relistic model representing typicl Gulf of Mexico slt structure. Strong wve conversions my occur t the interfces of sediments nd djcent slt odies. These wve conversions occur ecuse of the high velocity contrsts nd inhomogeneities, nd in generl (longitudinl) P-wves get scttered, refrcted nd converted due the stronger wve distortion effects of (longitudinl) P-wves t these strong velocity contrsts, yielding lrge shdow zones. On the other hnd, the converted (trnsversl) S-wves, propgte in generl in the slt odies with less wve front distortion ecuse of their lower propgtion velocity nd, therefore smller contrsts with the surrounding sediment P-wve velocities. Introduction In generl, when processing offshore dt, the top-slt events re picked nd P-wve slt flood migrtion is performed to determine the se-slt structure. The remining susurfce velocity model is eing estimted in step-wise pproch. To emphsize the importnce of S- wve propgtion inside slt odies, some experiments hve een performed on relistic model representing typicl Gulf of Mexico slt structure : the Ziggy model, shown in Figure 1. The Su-slt Multiples Attenution nd Reduction Technology Joint Venture (SMAART JV) relesed, to the industry nd universities, the 3-D numericl model referred to s Ziggy. The Ziggy geologic model represents generlized structure of explortion interest found long the Sigsee Escrpment in the deep wter Gulf of Mexico. The 3-D physicl Ziggy model (see Figure 1) is lyered model with complex slt structure, with dimensions of 38x42x10km depth (see lso vn Veldhuizen nd Blcquière, 2005). Mrine-type dt ws recorded over the 3-D Ziggy model, y plcing the model in the physicl modeling fcility t the Delft University of Technology (Blcquière nd Volker, 2002). Figure 2 shows picture of the Delft Experimentl Fcility for Imging. Specific susurfce scle models hve een designed nd plced in this wter tnk, for recording dt over relistic physicl models. In seismic dt imging, the susurfce model is not known nd due to wve conversions it often ecomes difficult to identify the se of slt nd su-slt structures. Lu et l. (2003) outlined the identifiction, removl nd imging of P-S conversions t slt-sediment interfces nd showed the importnce of tking wve conversions into ccount in migrtion. These situtions typiclly occur when recording offshore dt over susurfce contining slt odies (e.g. in the Gulf of Mexico). As mentioned erlier, recording offshore dt over susurfce with slt odies, strong wve conversions my occur t the top nd se of the slt ody. A lrge mount of this (longitudinl) P-wve energy gets converted into (trnsversl) S-wves nd these S-wves show up in the seismic dt s echoes of the P-wve reflections. (Ali nd Verschuur, 2006) outlined tht with the id of physicl model dt, these effects cn e studied in controlled mnner. Experiments on physicl model dtset illustrte clerly tht wve conversions pper t slt ody interfces nd tht migrtion of this dt for known susurfce model with the correct susurfce velocities (either P or S) will provide the correct imges of (multiply) mode-converted energy. Susurfce illumintion studies re very importnt in determining shdow zones in seismic dt. Xie et l. (2006) discussed one-wy wve-eqution sed method for seismic illumintion nlysis y extrpolting the wve fields from sources nd receivers to the susurfce trget. Acoustic nd elstic wve field propgtion Figure 3 shows 2-D verticl section from the 3-D Ziggy velocity depth model. As cn e oserved there is thinshped slt ody present in this section. The slt ody s used in this section contins velocities for (longitudinl) P- wve propgtion. To illustrte the importnce of (trnsversl) S-wve propgtion within slt odies, the following experiment hs een performed. The thinshped slt ody hs een replced with lower velocity eing the (trnsversl) S-wve velocity. Figure 3 shows the 2-D verticl section from the Ziggy model, the upper slt ody P-wve velocity hs een replced y S-wve velocity. Exmples Using oth 2-D sections from Figure 3, dt hs een modeled for (coustic) P nd (elstic) S wve field Tenth Interntionl Congress of the Brzilin Geophysicl Society

2 SUBSALT ILLUMINATION THROUGH P & S WAVE PROPAGATION 2 propgtion through the thin slt ody. Figure 4 shows vrious modeled snpshots for coustic nd elstic wve field propgtion. In Figure 4 P-wve snpshots re shown for 3 source loctions long the surfce. From these snpshots it cn e noticed, tht the wve fronts of the propgting P-wves get distorted, s the wve is propgting through high velocity contrsts etween sediments nd slt ody. Note tht in these exmples only trnsmission effects (downwrd one-wy wve field propgtion) re shown nd reflection effects re not considered here. However, the propgting wve front through the slt is the wve front tht illumintes the suslt structures. The more complex this wve front is, the more difficult it will e to imge these suslt structures. As the wve field hits the top of the slt ody, some distortion effect is clerly visile (see rrow in Figure 4). This effect, cusing tripliction in the wve front, is quite strong, nd is directly relted to the strength of the velocity contrst etween the sediments nd the top of the slt ody. A similr experiment hs lso een performed for the model depicted in Figure 3. In this model the P-wve slt ody hs een replced y lower (trnsversl) S-wve velocity. Becuse the velocity contrst is less thn the previous experiment (with P-wve slt ody), we expect less distortion effects, nd overll delyed suslt imges ecuse of the slower wve field propgtion inside the slt ody. Figure 4 shows the S-wve snpshots for 3 source loctions t the surfce (note here the delyed wves ecuse of slower S-wve velocity propgtion velocity through the susurfce model). From these snpshots comprisons, it cn e concluded tht for lrger velocity contrsts, the distortion effect of the wve front is lrger. Figure 4c shows the comined P- nd S-wve snpshots the lue colored wves represent P-wves nd the red colored wves represent S-wves. Figure 4d is lso comintion of P-wve nd S-wve snpshots ut for nother source loction t the surfce. In Figure 4d it lso oserved tht the S-wves hve higher illumintion ngle thn the P-wves. Note tht ecuse of the fst velocity ehvior of P- wves, the wve front gets distorted nd ecomes more complex nd loclly focused. On the other hnd less wve front distortion effects re oserved for propgting S-wves, due to the fct tht the S-wve velocity within the slt mtches more the P- wve velocities of the surrounding sediments. For etter illustrtion of the wve field propgtion, some illuminting ems re clculted nd illustrted in Figure 5. The illuminting ems re shown here for P-wve nd S-wve propgtion through the thin slt ody. Here the wve field is extrpolted from the surfce into the susurfce nd per depth level, the energy of the totl wve field hs eing clculted. Figure 5 shows the P- wve ems for 3 source loctions long the surfce. nd therefore my etter illuminte the se-slt nd suslt structures. Figure 5c shows the ddition of series of illuminting ems with sources long the surfce for only P-wves. Figure 5d shows the ddition of series of illuminting ems with sources long the surfce for only S-wve propgtion (in the slt ody). Notice tht P-wve propgtion cretes more shdow zones, nd note gin tht the S-wve propgtion etter illumintes the seslt nd suslt structures. Conclusions From the illumintion studies crries out on relistic model representing typicl Gulf of Mexico slt structure, it cn e concluded tht illumintion of the se-slt reflector nd the suslt region is etter otined y the wve field tht hve wve-conversion t the slt ody oundries, i.e. tht propgte with the P-wve velocity in the sediments nd with the S-wve velocity within the slt. Becuse the S-wve velocity within the slt mtches very well the P-wve velocities of the surrounding sediments, less distortion during the propgtion is oserved nd the illumintion of the suslt region is more uniform. On the other hnd, the full P-wve propgtion cretes strong inhomogeneities in the illumintion of the suslt structures, yielding lrge shdow zones. Acknowledgments The uthors would like to thnk the SMAART JV consortium for providing the ZIGGY model nd the sponsoring compnies of the DELPHI consortium for their finncil support. References Alá i, R, nd Verschuur, D.J., 2006, Suslt imging of wve converted reflections in physicl model dt, 68 th EAGE Conference & Exhiition. Blcquière, G. nd Volker, A.W.F., 2002, Physicl Modelling nd Suslt Illumintion, 64 th Mtg.: Eur. Assn. Geosci. Eng., C044. Lu, R.S., Willen D.E., nd Wtson, I.A., 2003, Identifying, removing nd imging P-S conversions t slt-sediment interfces, Geophysics, 68, vn Veldhuizen, E.J. nd Blcquière, G., 2005, Integrted pproch to cquisition geometry nlysis, 75th Ann. Internt. Mtg.: Soc. of Expl. Geophys., ACQ1.1. Xie., X., Jin, S. nd Wu, R., 2006, Wve-eqution sed seismic illumintion nlysis, Geophysics, 71, S169-S177 Figure 5 shows the S-wve ems for 3 source loctions t the surfce. Note tht S-wves get not distorted nd scttered s much s P-wves : the effect is tht S-wves propgte with higher illumintion ngle within slt odies

Figure 1. The 3-D Ziggy model. Figure 3.

) 2-D verticl section from the Ziggy model,

3 RIAZ ALAI *, JAN THORBECKE AND ERIC VERSCHUUR 3 ZIGGY model exploded view sltody ZIGGY model sltody Figure 2. The Delft Experiment Fcility for Imging. Figure 1. The 3-D Ziggy model. Figure 3. ) 2-D verticl section from the Ziggy model. ) 2-D verticl section from the Ziggy model, the upper slt ody P-wve velocity hs een replced y S-wve velocity.

SUBSALT ILLUMINATION THROUGH P & S WAVE PROPAGATION 4 c d Figure 4.

P-wve snpshots for 3 source loctions long the surfce.

delyed wves ecuse of slower S-wve propgtion velocity through the susurfce

c) Comined P- nd S-wve snpshots the lue colored wves represent P-wves nd

d) Sme s c), ut for nother source loction t the surfce.

4 SUBSALT ILLUMINATION THROUGH P & S WAVE PROPAGATION 4 c d Figure 4. Vrious modeled snpshots for coustic nd elstic wve field propgtion : ) P-wve snpshots for 3 source loctions long the surfce. ) S-wve snpshots for 3 source loctions long the surfce (note here the delyed wves ecuse of slower S-wve propgtion velocity through the susurfce model). c) Comined P- nd S-wve snpshots the lue colored wves represent P-wves nd the red colored wves represent S-wves. d) Sme s c), ut for nother source loction t the surfce. Note tht ecuse of the fst velocity ehvior of P-wves, the wve front gets distorted nd gets more complex nd focused. On the other hnd for S-wves the wve front distortion effects re less oserved (propgtion with higher illumintion ngle).

RIAZ ALAI *, JAN THORBECKE AND ERIC VERSCHUUR 5 c d Figure 5.

source loctions long the surfce. ) S-wve ems for 3 source loctions long the surfce.

Therefore, the S-wves my e etter suited to illuminte the se-slt nd suslt structures.

d) Addition of series of illuminting ems with sources long the surfce for only S-wves (in

5 RIAZ ALAI *, JAN THORBECKE AND ERIC VERSCHUUR 5 c d Figure 5. Illuminting ems showing the wve propgtion through the susurfce model : ) P-wve ems for 3 source loctions long the surfce. ) S-wve ems for 3 source loctions long the surfce. Note tht S-wves do not get distorted nd scttered s much s P-wves. Therefore, the S-wves my e etter suited to illuminte the se-slt nd suslt structures. c) Addition of series of illuminting ems with sources long the surfce for only P-wves. d) Addition of series of illuminting ems with sources long the surfce for only S-wves (in the slt ody). Notice tht P-wve propgtion cretes more shdow zones, nd note gin tht the S-wve propgtion illumintes etter the se-slt nd suslt structures.

Fully Kinetic Simulations of Ion Beam Neutralization

Fully Kinetic Simulations of Ion Beam Neutralization Fully Kinetic Simultions of Ion Bem Neutrliztion Joseph Wng University of Southern Cliforni Hideyuki Usui Kyoto University E-mil: josephjw@usc.edu; usui@rish.kyoto-u.c.jp 1. Introduction Ion em emission/neutrliztion