Geological Society, London, Special Publications-2003-Nieuwland-1-5

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Geological Society, London, Special Publications

doi: 10.1144/GSL.SP.2003.212.01.012003; v. 212; p. 1-5Geological Society, London, Special Publications

D. A. Nieuwland

modellingIntroduction: new insights into structural interpretation and

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I n t r o d u c t i o n : n e w i n s i g h t s i n t o s t r u c t u r a li n t e r p r e t a t i o n a n d m o d e l l i n g

D . A . N I E U W L A N DF a c u l t y o f E a r th a n d L i f e S c i e n c es , T e c to n ic s , V r i j e Un iv e r s it e it , D e B o e le la a n 1 0 8 5,

1 0 8 1 H V A m s t e r d a m , T h e N e t h e r l a n d s ( e -m a i l : d i c k . n i e u w l a n d @ f a l w , v u .n l )

This book i s a fo l low-up to a Geo log ica l Socie tyo f L o n d o n c o n f e r e n c e w i t h t h e s a me t i t l e , h e l d i nBu r l i n g t o n H o u s e , L o n d o n , i n Fe b r u a r y 2 0 0 0 . Fo l -l o w i n g t h e c o n f e r e n c e i t w a s d e c i d e d t o c o mp i l e aSp e c i a l Pu b l i c a t io n b a s e d i n p a r t o n p a p e r sp resen ted a t the conference and in par t on paperstha t were added l a t e r to fo rm a ba lanced con ten t .T h e c o n t e n t o f New Insights into StructuralInterpretation and Modelling presen t s a ba lancedoverv iew of what the t i t l e p romises . I t i s in t endedas a book tha t wi l l s e rve the exper i enced p ro -fess ional as wel l as more advanced s tuden t s inE a r t h s c i e n c e s w i t h a w i d e r a n g e o f t o p i c sd e s c r i b e d i n h i g h q u a l i t y p u b l ic a t io n s . So me c h a p -te rs a re by l eaders in the f i e ld , o ther chap ters a rew r i t t e n b y y o u n g a u t h o r s w i t h f r e s h i d e a s .

St ruc tu ra l in t e rp re ta t ion and model l ing go handin hand in s t ruc tu ra l geo logy . In te rp re ta t ion needsto be based on da ta . These da ta can be found onma n y s c a l e s a n d i n v o l v e d i r e c t o b s e r v a t i o n s o fn a t u r a l p h e n o me n a b a s e d o n f i e l d w o r k , a n di n d i r e c t o b se r v a t io n s o f n a t u r a l d a t a b y s u c h m e a n sas se i smic o r s t res s measurements . In te rp re ta t ion i sn o l o n g e r l i m i t e d t o d r a w i n g l i n e s a l o n g f a u l tp lanes in c ross -sec t ions o r to cons t ruc t ing hor izonma p s . N e w me t h o d s a n d t e c h n i q u e s h a v ed e v e l o p e d i n m a n y f ie l d s o f a c q u i s it i o n p r o c e s s in ga n d i n t e r p r e t a t i o n . Mo d e l l i n g r e l i e s o n t w o c o mp -l e me n t a r y a p p r o a c h e s : a n a l o g u e mo d e l s u s i n gphys ica l mater i a l s as ana logues to rocks , andn u me r i c a l mo d e l s t h a t a r e b a s e d o n ma t h e ma t i c a la l g o r i t h ms t o mi mi c r o c k s a n d d e f o r ma t i o n p r o -c e s s e s w i t h c o mp u t e r p r o g r a ms .

T h e s e a p p r o a c h e s t o s o l v i n g c o m p l e x s t ru c t u ra lp r o b l e ms h a v e t h e i r s p e c i f i c a d v a n t a g e s a n d l i mi -t a t ions . S ign i f i can t p rogress in s t ruc tu ra l geo logy i stherefo re to be expected due to improved in teg ra tedmethods . In th i s book a co l l ec t ion o f papers hasb e e n c o mp i l e d w i t h t h e i n t e n t i o n t o p r o v i d e t h er e a d e r w i t h a c o mp r e h e n s i v e o v e r v i e w o f s t a t e - o f -the-ar t approaches and t echn iques in s t ruc tu ra lin te rp re ta t ion and model l ing . The chap ters a reo r g a n i z e d f o l l o w i n g t h e v i e w t h a t t h e t o p i c s t h a tare c loses t to the na tu ra l wor ld appear f i r s t , fo l -

l o w e d b y g r a d u a l l y mo r e ' a r t i f i c i a l ' a p p r o a c h e s .A l t h o u g h t h e mu l t i d i s c ip l i n a r y n a t u r e o f ma n y p a p -e r s ma k e s a s t r a i g h t f o r w a r d o r d e r o f a p p e a r a n c eaccord ing to top ic d i f f i cu l t , t he chap ters dea l ingw i t h n a t u r a l g e o l o g i c a l d a t a a p p e a r i n p r i n c i p l ee a r l y , i n t e r p r e t a t i o n p r e c e d e s mo d e l l i n g a n d a n a -l o g u e mo d e l l i n g p r e c e d e s n u me r i c a l mo d e l l i n g .

S i n c e t h e p u b l i c a t i o n o f t h e p r e d e c e s s o r o f t h i sSp e c i a l Pu b l i c a t i o n ( Bu c h a n a n & N i e u w l a n d 1 9 9 6)mu c h p r o g r e s s h a s b e e n ma d e . T h i s h a s b e e n p r i m-a r i l y th a n k s t o t h e c o n t i n u o u s l y i n c r e a s i n g c o m p u t -i n g s p e e d a n d c o mp u t e r me mo r y c a p a c i t y , w h i c hhas pos i t ive ly a f fec ted a l l f i e lds in s t ruc tu ra lin te rp re ta t ion , se i smics and model l ing , d i rec t ly o rind i rec t ly .

InterpretationN a t u r a l d a t a s e t s h a v e t h e o b v i o u s a d v a n t a g e t h a tt h e y a r e r e a l , h o w e v e r s t r a n g e t h e y ma y a p p e a r t obe . The da ta resu l t d i rec t ly f rom natu ra l defo r -ma t i o n p r o c e s s e s t h a t h a v e d e f o r me d n a t u r a l r o c k sin na tu ra l t ime. However , da ta f rom ou tcrops a l sohave p rob lems assoc ia ted wi th them. I t i s o f t en d i f -f i c ul t o r e v e n i m p o s s i b l e t o o b s e r v e a n d m e a s u r e afea tu re ( fau l t , fo ld o r f rac tu re) comple te ly in 3D.Co mmo n l y s o me e l e me n t s n e e d t o b e e s t i ma t e db e c a u s e t h e y c a n n o t b e o b s e rv e d . A n o t h e r p r o b l e mwi th na tu ra l da ta i s the t ime fac to r . Deformat ionp r o c e s s e s t h a t t o o k p l a c e o v e r g e o l o g i c a l t i me -s c a l e s c a n n o t b e o b s e r v e d i n a h u ma n l i f e t i me .What we see in ou tcrop i s a s t a t i c end resu l t o f av e r y d y n a mi c p r o c e s s . T h e 3 D p r o b l e m w i t h n a t u -r a l d a t a i s i n p a r t r e s o l v e d w h e n 3 D s e i s mi c c a nb e a p p l i e d . U n f o r t u n a t e l y t h e me t h o d i s c o s t l y a n dt h e r e fo r e a l mo s t e x c l u s i v e l y u s e d f o r c o mm e r c i a lp u r p o s e s , p r e f e r a b l y o n o f f s h o r e l o c a t i o n s w h e r ethe acqu i s i t ion i s so much be t t e r and eas ie r than inthe mounta inous a reas where f i e ld geo log i s t s o f t enl i k e to w o r k b e c a u s e o f t h e a b u n d a n c e o f o u tc r o p -p i n g r o c k s . T h e q u a l i t y o f 3 D s e i s mi c h a si mp r o v e d s i g n i f ic a n t l y o v e r t h e l a s t t e n y e a r s o r s o .I t has become a s t andard too l fo r geo log i s t s and

From: NmUWLAND, D. A. (ed.) New Insights into Structural Interpretation and M odelling. Geological Society, Lon-don, Sp ecia l Publications, 212 , 1-5. 0305-8719/03/515 The Geological Society of London 2003.


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2 D.A . NIEUWLANDi s n o l o n g e r t h e ex c l u s i v e d o m a i n o f t h e t r a i n edgeophys ic i s t / se i smic in terpre ter .T h e s ec t io n o n i n t e rp re t a ti o n b eg i n s w i t h a ch ap -t e r b y Ce l l o e t a l . The work re l i es on a l a rge data-b as e co l l ec t ed i n t h e A p en n i n es . T h e p ro j ec t w asb as ed o n co l l ab o ra ti o n b e t w een i n d u s t ry an d acad -em i a , a co m b i n a t i o n t h a t m ay b eco m e m o re co m -mon in the near fu ture . Indus t ry has decreased i t so w n r e s ea rch e f fo r t s an d r e l i e s m o re h eav i l y o nu n i v e r s i t y p ro j ec ts , f o cu s ed o n g e o l o g i ca l p ro b l em sthat a re o f in teres t to the indus t ry . The chap ter byCe l l o e t a l . i l lus t ra tes tha t fo r f rac ture sys tems ,f i e ldwork i s s t i l l the m os t impor ta n t source o fin format ion .Deta i l s o f complex fau l t s t ruc tures can be in ter -p re t ed v e ry w e l l f ro m h i g h - r e s o l u t i o n 3 D s e i s m i c ,a s d em o n s t r a t ed b y t h e ex am p l es i n t h e ch ap t e r b ySch ro o t & d e H aan . H o w ev e r , f au l t s w i t h an o f f se tsmal ler than some 20 m cannot be in terpre tedre l i ab ly and t ens ion f rac tures cannot be observedat a l l . Nine-component se i smic may be ab le toiden t i fy t ens ion f rac tur ing ( jo in t s ) , bu t cannot d i s -t i n g u i s h b e t w een a f ew l a rg e f r ac tu re s an d m an ysmal l f rac tures . Or ien ta t ions o f t ens ion f rac tures y s t em s d e r i v ed f ro m s e i s m i c d a t a a r e a l s o u n ce r -t a in because con jugate f rac tures t end to becomeaveraged a long the b i sec t r ix o f the acu te ang le .N ev e r t h e l e s s , w i t h o u t 3 D s e i s m i c t h e re w o u l d b en o h o p e o f i n t e rp re t i n g t h e v as t an d co m p l ex s u b -surface s t ruc tures tha t fo rm reservo i rs fo r na tura lresources such as o i l and gas . The message i sagain , in tegra t ion of f i e ldwork , model l ing and se i s -mics , to combine fu l l 3D and in t r i ca te fau l t geo-met r i es a t a l l sca les i s the key to re l i ab le s t ruc-tu ra l in terpre ta t ion .Next to fau l t geomet r i es , the k inemat ics o f fau l t -ing processes i s jus t as impo r tan t , p resen t ing ap ro b l em i n an o t h e r d i m en s i o n - t i m e . O n eapproach to the k inemat ics p rob lem i s tha t o f pa l -inspas t i c recons t ruct ion , which presen t s p rob lemsof i t s own. Trad i t ional ly , pa l inspas t i c recons t ruc-t ion (o r sec t ion balancing) can on ly be per formedon d ip sec t ions o f s t ra ta tha t were deformed inp la in s t ra in . As many deformat ions t ake p lace in3D, a pa l inspas t i c recons t ruct ion requ i res a 3Dapproach a l so . In o rder to recons t ruct fau l t s cor-rec t ly in 3D, one needs to know the comple tes t ra in -path . Preservat ion of l ine l eng th and area i snecessary , bu t no t suf f i c ien t to per form a mechan-ica l ly correc t pa l inspas t i c recons t ruct ion ; the s t ra inpath needs to be incorpora ted as wel l .Ru t t en & V er s ch u ren h av e w o rk ed o u t a 3 Dapproach to th i s p rob lem. They app ly the i r t ech-n ique on the sca le o f a de lt a . To a t t ack th i s p rob lemo n t h e m u ch l a rg e r s ca le o f m o u n t a i n b e l t s , H i n d l ehas developed a t echnique tha t can be seen as s imi -l a r t o t h a t u s ed b y Ru t t en & V er s ch u ren i n t h a ti t i s a l so based on d i sp lacement pa ths . However ,

Hind le ' s approach i s speci f i ca l ly su i t ab le fo r ther eco n s t ru c t i o n o f d i s p l acem en t s o n a m u ch l a rg e rsca le . In h i s example he uses d i sp lacement f i e ldsr a t h e r t h en v ec t o r s t o r eco n s t ru c t m o v em en t s o nthe sca le o f mounta in be l t s ra ther than a long ind i -v idual fau l t s .Pro jec t s in the o i l and gas indus t ry and in c iv i leng ineer ing rou t ine ly requ i re accura te s t ruc tura lin terpre ta t ions o f compl ica ted fau l t sys tems and there la ted s t ress f i e lds . Accura te def in i t ion of thepresen t -day t ec ton ic s t ress i s a fundamenta lr eq u i r em en t t o p e r fo rm s u ch t a s k s co r r ec t l y an dre l i ab ly . The re l i ab i l i ty o f the resu l t s depends to alarge ex ten t on the qual i ty assurance of the da ta .T h e r eq u i r em en t s fo r t h i s q u a l i t y a s s e s s m en t an di m p l em en t a t i o n h av e b een l a i d d o w n i n a p ro g ramca l l ed T E N SO R. T h e p ro g ram i s th e b as ic t o o l f o rthe World St ress Map bu t a l so has o ther app l i -ca t ions in the f i e ld o f s t ress invers ion . Delvaux &Sp ern e r ex p l a i n m o re ab o u t t h i s w i d e l y u s ed p ro -g ram . T h e Wo r l d S t r e s s M ap p ro v i d es t h e d a t a i nthe fo rm of a f ree ly access ib le g lobal da tabase asd es c r i b ed i n t h e ch ap t e r b y Sp e rn e r e t a l .A di f feren t f i e ld o f s t ruc tura l in terpre ta t ion wi thre levance fo r modern socie ty i s tha t o f ear thquakem ech an i c s . P r ed i c t i n g ea r t h q u ak es h as b eenat t empted for decades i f no t longer , bu t so far p re-d ic t ions have no t been very success fu l . In a newunconvent ional approach to ear thquake pred ic t ion ,Vol t i & Crampin presen t an app l ica t ion of se i smicshear-wave sp l i t t ing , based on a long- term f i e lds tudy . The f i r s t chap ter on th i s top ic descr ibes thebackground , p re l iminary observat ions , and analys i sof shear-wave sp l i t t ing in Ice land . The secondchapter d i scusses po ten t i a l app l i ca t ions o f th i sap p ro ach i n c l u d i n g m o n i t o r i n g h y d ro ca rb o n p ro -duct ion , s t ress - forecas t ing ear thquakes and somevolcan ic erup t ions .

ModellingIn t h i s t i m e o f m as s i v e co m p u t i n g p o w er a co m -m o n l y a s k ed q u es t i o n w i t h r eg a rd t o an a l o g u emodel l ing (AM) i s , does i t s t i l l have a p lace insc ience , and why no t so lve a l l our p rob lems wi thco m p u t e r s ? T h i s s i m p l e q u es t i o n i m m ed i a t e l ybr ings fo rward the s t reng ths and weaknesses o fbo th model l ing t echniques . In the model l ing sec-t ion a b r i ef t rea tment o f some fundamenta l aspect so f an a l o g u e m o d e l l i n g an d n u m er i ca l m o d e l l i n g(NM) i s p resen ted .In an a l o g u e m o d e l l i n g t h e s m a l l s i ze o f th e m o d -el s d i rec t ly ra i ses ques t ions about sca l ing . (Mandl1 9 8 8 ; M cCl ay 1 9 9 0 ; Bru n e t a l . 1994). The resul tso f co m p u t e r m o d e l s a r e s eem i n g l y fr ee o f a s ca li n gp ro b l em , e s p ec i a l l y w h en m o d e l r e s u l t s a r e g i v endimens ions tha t a re o f the same order as in na tura lexamples . Th i s i s mis lead ing in tha t , fo r example ,


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INTRODUCTION 3in the much used finite element (FE) technique, thesize of the mesh elements is very large comparedto the smallest elements in natural deformation pro-cesses. For comparison, a typical analogue modelcontains about 30000000 sand grains. In order toreach the same resolution as such an AM experi-ment, a FE mesh should also be built of 30000000elements. FE meshes of such dimensions are stillunthinkable. The sand grains in analogue modelsare not scaled; in a typical model 1:10000 to1:100000 sand grains with an average diameter of0.1 mm would resemble boulders of roughly 1 m to10 m in size. However, the resolution of analoguemodels in terms of definition of individual faultplanes and intricate fault patterns is much greaterthan in numerical models. Without going into themathematics of scaling, a good argument in sup-port of the validity of scaled analogue modelscomes from nature itself. Field observations offaults of all types on almost all scales, indicate thatfractal properties can be applied to faulting andfracturing (Mandelbrot 1989). Self-similarity hasas a consequence that small fault systems createdin analogue models have a similar geometry aslarger scale systems.Whereas numerical models rely on mathematicalalgorithms to mimic natural processes andmaterials, analogue models work with naturalmaterials to mimic rocks; however, the defor-mation processes are all natural, not imitated byalgorithms. A disadvantage of using analoguematerials to simulate rocks is that the choice ofmaterials is limited compared to the variation innatural rocks. For most brittle rocks this does notpose a problem. The reason is that the mostimportant mechanical parameter that governsdeformation geometries and processes is theinternal frict ion angle ~b, which is about 30 formost br ittle rocks and is also about 30 for sand.The main difference between sand and rocks isstrength; however, strength governs only the mag-nitude of the stress that is required to drive a defor-mation process. The resulting structural geometriesare independent of the stress magnitude. For bothmethods (AM and NM) scaling is a real but man-ageable problem: not everything can be exactlyscaled, but most of the important paramete rs canbe scaled satisfactorily.

The main goal o f analogue models is to study thegeometries and kinematics of tectonic deformationprocesses in manageable space and time. The dur-ation of the deformation process (strain rates), highresolution and free formation of faults are of funda-mental importance to this method.Stress orientations and magnitudes are muchmore difficult to acquire from AM experimentsthan geometric and kinematic information. So faronly directional point measurements are possible.

Such a stress measurement has an advantage ofbeing continuous in time, but it is limited to beinga point in 3D space. Numerical models lack muchin the field of geometry and to a lesser extent kin-ematics because free-growing faults cannot yet begenerated. However, concentrations of deformat ionin shear bands can give useful information:especially in the early deformation stages, stressescalculated with numerical methods are much moredetailed than the AM point measurements eventhough the NM stress measurements are not con-tinuous in time.So far deformat ion in the brittle domain has beendiscussed. When viscous or ductile materials startto play a role, the material properties become moreimportant. In numerical models material propertiescan be varied more easily than materials in ana-logue models. However, the viscous material sili-cone putty in a variation of qualities can be modi-fied to suit many desired mechanical properties andstepping engines provide the required control overstrain rates. Temperature effects are still a majorproblem in analogue experiments. Numerical mod-els can treat this aspect better by simply varyingthe input parameters in algorithms that are hope-fully realistic enough to model the processes thatwe are trying to understand.

A n a l o g u e m o d e l l i n gThe contribution by Dooley et al. is a good illus-tration of an integrated approach in which field data(from seismic) and modelling have been broughttogether to interpret and understand a complexmultiphase fault system. The example also makesclear the importance of stratigraphy for reli ablemodelling and interpretation of deformation pro-cesses. The mechanical stratigraphy is the basis fora good model, be it analogue or numerical. In thechapter by Schellart & Nieuwland the emphasislies on the kinematics of a growing complex faultsystem, and the related changes in the local stressfield. The results make clear that with an unchang-ing regional stress field, the local stresses within astructure can change dramatically. The work makesintensive use of computed tomograph (CT) scan-nin g to generate 3D data volumes. CT scans permitnon-destructive acquisition of 3D data volumes ofanalogue models. The resulting series of 3D datavolumes through time forms a powerful 4D data-base for detailed structural interpretation that canbe performed on 3D seismic interpretation systems.This implies that advances made in 3D seismicsoftware are also of immediate use for the analysisand interpretation of analogue models that havehad the benefit of CT scanning. Tentler & Tem-perley have focused their analogue modelling on alarge scale of deformation including the asthenos-


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4 D.A. NIEUWLANDphere, which they approximate with carefullychosen sili con polymers of two different viscositiesand densities. The model highlights the strength ofanalogue modelling in representing the develop-ment of intricate 3D structures in time, and at thesame time demonstrates the complexity of makingthe appropriate analogue materials for experimentsthat include layers with brittle and ductile or vis-cous behaviour.Mulugeta & Sokoutis have applied analoguemodelling to gain more insight into the mechanicsof thrust tectonics. Their chapter describes the useof analogue experiments for studying the dynamicand rheologic control of hanging wall accommo-dation in ramp-fiat thrust models. The complexityof 3D deformation processes in time becomes moreapparent as strain rate and rheology are also usedas variables. Much can be learned from such ana-logue models about the strain path of complicatedstructures. The study highlights the usefulness ofmodelling tectonic processes with analoguematerials and at the same time draws attention tothe practical difficulty involved with such models.Variations in material are much more easily achi-eved in numerical models, but here the algorithmsthat need to be applied form another challenge.

N u m e r i c a l m o d e l l i n gFollowing the observations and conclusions of theanalogue models, the next logical step is to find outhow numerical techniques can be applied to findanswers to questions that cannot be solved by ana-logue modelling. In their chapter Burov & Poliakovuse a numerica l approach to model basin dynamics.The work is exemplary for numerical modelling.In addition to the main topic of the paper, erosionalforcing of basin dynamics, they present advancesin the mathematics of 3D basin modelling. Thework also demonstrates the quantitative insightsthat can be gained from this approach and that aresuch a welcome complementary result to the morequalitative analogue experiments. Burov & Pol-iakov and also Robin e t a l . work with a variablethat has not yet been successfully controlled in ana-logue models - temperature. In analogue modelsof the brittle upper crust, temperature effects arenormally not a factor that needs to be considered;however, as soon as the deeper lithosphere orasthenosphere is involved in the modelling, tem-perature effects become important. Robin e t a l .integrate a wealth of geological data with theirnumerical work.

The chapter by Hobbs e t a l . deals with 3D seis-mic data, a field in which a lot o f progress has beenmade over the last five years. Hobbs e t a l . havewritten an important contribution on seismic pro-cessing of difficult data with severe topography

effects and velocity problems. Their approach hasnow been applied to an interesting geoscienceproblem, that of imaging an axial magma chamberon the East Pacific Rise, but cou ld well be modi fiedfor application to economic targets as well.

The next chapter on geomechanical modellingby Heidbach & Drewes deals with a large-scaleproblem - tectonic processes in the Eastern Medit-erranean. Although their approach is to a largeextent based on geomechanics with an elasto-visco-plastic 3D finite element model at the core,important boundary conditions still need to be pro-vided as input. The mode l does not generate faults;however, on the scale of the problem individualfaults are not so important. 3D geomechanicalfinite element models are still in a developmentstage and this paper marks a significant step for-ward.The next two chapters, by Cornu e t a l . , avoid theproblem of 3D geomechanics by using a kinematicapproach to large scale geometrical problems. Adisadvantage of this is that input of fault geo-metries is required, but an advantage is that rela-tively complicated structural geometries can bemodelled. Cornu e t a l . describe their approach andapply it to three cases: basin deformation, and com-pressional and extensional tectonics.

In the last two chapters, Skar &Beekman andvan Wees e t a l . apply geomechanical finite elementmodell ing to problems on smaller scales than entirebasins and limit themselves to the brittle uppercrust. The method is possible in the case workedon by Skar & Beckman because it is not necessaryto grow faults; they are part of the startinggeometry and derived from well defined geologicalcross-sections. The complicated structural cross-section that has been used as the basis for theirwork could be used because the model is 2D. Thework demonstrates that in many cases, where it isvalid to approximate the deformation history withplain strain, there is a definite advantage in using2D instead of 3D. As the lithosphere is notinvolved, the rheological model can be elasto-plastic, a viscous element is not required. VanWees e t a l . also base their calculations on a wealthof geological and geophysical data. They integratethese in a geomechanical 3D finite element modeland successfully model the quantitative effects ofhydrocarbon depletion from reservoirs.From the chapters on numerical modelling it canbe concluded that numerical modelling and ana-logue modelling are indeed complementary inmany ways. Both methods continue to evolve andto produce new approaches and techniques. Geo-mechanical numerical models cannot yet generatefree-growing faults; however, in very large scaleproblems individual faults are not so important andgeomechanical numerical models can produce


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I N T R O D U C T I O N 5r e a l i s t i c r e s u l t s . O n s c a l e s w h e r e i n d i v i d u a l f a u l t sb e c o m e i m p o r t a n t t h e t e c h n i q u e t h a t i s m o s t s u i t -a b l e d e p e n d s o n t h e n a t u r e o f t h e p r o b l e m .W h e t h e r a k i n e m a t i c o r a m e c h a n i c a l a p p r o a c h i sc h o s e n d e p e n d s o n t h e q u e s t i o n t h a t n e e d s t o b ea n s w e r e d .

AcknowledgementsT he ed i to r w i s hes to thank the G eo log ica l Soc ie ty o f L on-don fo r g iv ing the o ppor tu lf i ty to o rgan ize the co nfe rencewhich in s p i red th i s vo lume and the i r s ubs equen t s uppor tdu r ing the compi la t ion o f th is book . T he boo k wou ld no thave appea red w i thou t the he lp o f the re fe ree s who s pen tcons ide rab le t ime rev iew ing the m anus c r ip t s. T he fo l low-ing re fe ree s a re g ra t e fu lly acknow ledged : G . Be r to t ti ; T .den Bezemer; J .C. Blom; P. v .d . Boogaert ; S. Cloet ingh;T . Dooley; H. Dous t ; T . van Eck; R. Gabrie lsen; O. Heid-bag; D. H indle ; F. Kets ; Y. Leroy ; I . Mo ret t i ; F. J. N ieuw -

land; J . Rei js ; P. Richard; K. Rut ten; W. Schel lar t ; A.Se ih l ; J .D . v an Wees ; B . F . Wind ley and R . Z oe tem e i j e r .

ReferencesBRUN , J., SOKO UTIS,D. & VAN DEN DRIESSCHE, J. 1994.

A n a l o g u e m o d e l l i n g o f d e t a c h m e n t f a u lt s y s t e m s a n dcore complexes . Geology, 22 , 319-322 .BUCHANAN, P. G . & NIEUWLAND, D. A. (eds) 1996.Modern Ins ights into Structural Interpretat ion, Val i -da t ion and M ode l l ing . Geolog ica l Soc ie ty , L ondon ,Specal Publ ica t ions , 99.MANDELBROT, B. 1989. M ultifrac tal me asur es, esp ecia llyfo r the geophys ic i s t . Geophysics, 1/2, 5-42.MANDL, G. 1988. Mecha nics o f tec tonic faul t ing. In :ZWART, H. J. (ed.) Deve lopmen ts in S t r uc tur a lGeology. E ls ev ie r , Ams te rdam.McCLAY, K. R. 1990. Extens ional faul t sys tem s in sedi-men ta ry ba s ins . A rev iew o f ana logue mode l s tud ie s .Marine and Petroleum Geology, 7 , 206-233 .

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Geological Society, London, Special Publications-2003-Nieuwland-1-5