Ch 9 Structures

8/17/2019 Ch 9 Structures

1/132

Rock Structure and Fault

Activitychapter 9


2/132

What is structural geology

The study of the forms of the Earth’s crustand the processes which have shaped it

analysis of displacement and changes in

shape of rock !odies "strain# reconstruct stress that produced strain


3/132

Structural $eformation

Rocks deform whenstresses placed uponthem e%ceed the rock

strength &rittle deformation

"e'g' fractures#

ductile deformation

"e'g' folds#


4/132

$riving Forces

(late tectonics ) plate convergence and ridgespreading

$eep !urial of sediments

Forceful intrusion of magma into the crust *eteorite impacts


5/132

Evidence of +rustal

$eformation Folding of strata Faulting of strata

Tilting of strata ,oints and fractures


6/132

Evidence of +rustal

$eformation Folding of strata

Faulting of strata

Tilting of strata

,oints and fractures


7/132

Evidence of +rustal

$eformation Folding of strata

Faulting of strata

Tilting of strata

,oints and fractures


8/132

Evidence of +rustal

$eformation Folding of strata Faulting of strata

Tilting of strata ,oints and fractures


9/132

Applications of structural

geology su!surface e%ploration for oil and gas

mining e%ploration

geotechnical investigations

groundwater and environmental siteassessment


10/132

-eological structures

-eologic !ed contacts

(rimary sedimentary structures

(rimary igneous structures

Secondary structures


11/132

Fundamental Structures

Three fundamental types of geologicstructures.

bed contacts primary structures / produced duringdeposition

or emplacement of rock !ody

secondary structures / produced !ydeformation

and other process after rock is emplaced


12/132

Bed Contacts

&oundaries which separate one rockunit from another

two types.0' 1ormal conforma!le contacts

2' 3nconforma!le contacts

"4unconformities’#


13/132

Conformable Bed Contacts

5ori6ontal contact !etween rock unitswith no !reak in deposition or

erosional gaps no significant gaps in geologic time

&ook +liffs7central 3tah


14/132

Unconformable Contacts

Erosion surfaces representing asignificant !reak in deposition "and

geologic time# angular unconformity

disconformity non/conformity


15/132

Angular Unconformity

&edding contact which discordantly cutsacross older strata discordance means strata are at an angle to

each other

commonly contact is erosion surface


16/132

Formation of an angular

unconformity


17/132

DisconformityErosional gap !etween rock units

without angular discordance

e%ample. fluvial channel cutting intounderlying se8uence of hori6ontally!edded deposits


18/132

Nonconformity

Sedimentary strata overlying igneous ormetamorphic rocks across a sharp contact

e%ample. (recam!rian/(aleo6oic contact in ntario

represents a erosional hiatus of a!out :;; ma

-rand +anyon7 3SA


19/132

Structural Relations

The structural relations !etween !edcontacts are important in

determining.0' presence of tectonic deformation


20/132


21/132

Principle of Cross!cutting

>gneous intrusions and faults are younger than the rocks that they

cross/cut

*afic dike cutting across older sandstones


22/132

Cross!cutting Relations

ften several cross/cuttingrelationships are present

how many events in this outcrop?


23/132

Principle of "nclusion

Fragments of a rock included within a

host rock are always older than thehost


24/132

Fundamental Structures

Three fundamental types ofstructures.

!ed contacts primary structures

secondary structures


25/132

Primary SedimentaryStructures

Structures ac8uired during deposition ofsedimentary rock unit

Stratification / hori6ontal !edding is mostcommon structure in sedimentary rocks

http://wrgis.wr.usgs.gov/docs/parks/rxmin/laminSS215x192.jpg


26/132

Primary Sedimentary

StructuresCross!bedding / inclined stratification

recording migration of sand ripples or

dunes


27/132

Primary Sedimentary

Structures

Ripples / undulating !edforms produced !y

unidirectional or oscillating "wave# currents


28/132

Ripplemar#s


29/132

Primary Sedimentary

Structures$raded bedding / progressive decrease in

grain si6e upward in !ed

indicator of upwards direction in deposit common feature of tur!idites


30/132

Primary Sedimentary

Structures%ud crac#s / cracks produced !y

dessication of clays


31/132

Primary Sedimentary

StructuresSole mar#s / erosional grooves and marks

formed !y scouring of !ed !y unidirectional

flows good indicators of current flow direction


32/132

Primary Sedimentary StructuresFossils ) preserved remains of organisms7 casts or

moulds good strain indicators

determine strain from change in shape of fossil

relative change in length of lines


33/132


34/132

Primary "gneous Structures

Flo& stratification layering in volcanic rocks produced !y

emplacement of successive lava

sheets stratification of ash "tephra# layers


35/132

Primary "gneous Structures

Pillo& la'as / record e%trusion and8uenching of lava on sea floor


36/132

"mportance of Primary

Structures() Paleocurrents / determine paleoflow directions

*) Origin ) mode of deposition7 environments

+) ,ay!up / useful indicators of the direction of younger !eds in stratigraphic se8uence

-) Dating / allow relative ages of rocks to !e

determined !ased on position7 cross/cutting

relations and inclusions.) Strain indicators / deformation of primary

structures allows estimates of rock strain


37/132

Secondary Structures

Secondary structures / deformationstructures

produced !y tectonic forces and otherstresses in crust(rinciple types.

fractures


38/132

Fractures and /oints

Fractures ) surfaces along which rockshave !roken and lost cohesion

/oints / fractures with little or nodisplacement parallel to failuresurface

indicate !rittle deformation of rock


39/132

Fractures and /oints


40/132

Faults

Faults / fracture surfaces with apprecia!ledisplacement of strata

single fault plane

fault 6one / set of associated shear fractures

shear 6one / 6one of ductile shearing


41/132

S0ear 1ones

S0ear one / 6one of deformed rocks that are morehighly strained than surrounding rocks

common in mid/ to lower levels of crust shear deformation can !e !rittle or ductile


42/132

Fault 2erminology

Hanging &all bloc#/ fault !lock toward whichthe fault dips

Foot&all bloc# / fault !lock on underside offault

Fault plane ) fault surface


43/132

Fault Slip

Slip is the fault displacement descri!ed!y.

direction of slip sense of slip

magnitude of slip


44/132

Fault 2ypes

Dip!slip faults / slip is parallel to thefault dip direction

normalreverse

thrust


45/132

Fault 2ypes

Normal fault / footwall !lock dispacedup


46/132

Fault 2ypes

Re'erse 3t0rust4 fault / footwall !lockdisplaced down


47/132

Fault 2ypes

Stri#e!slip ) fault slip is hori6ontal7parallel with strike of the fault plane

right/handed "de%tral# left/handed "sinistral#


48/132

Fault 2ypes

Obli5ue slip ) +om!ination of dip/ andstrike/slip motion

de%tral/normal de%tral/reverse

sinistral/normal

sinistral/reverse


49/132

Faults

What type of faults are shown here?


50/132

Faults



51/132

Faults



52/132

Faults



53/132

Folds

Folds ) warping of strata produced !ycompressive deformation

range in scale from microscopic featuresto regional/scale domes and !asins

indicators of compression and shortening


54/132

Fold 2erminology

Hinge 3A6ial4 plane / imaginary plane !isecting foldlim!s

Hinge line / trace of a%ial plane on fold crest

Plunge / angle of dip of hinge line


55/132

hori6ontal fold a%is


56/132


57/132

Fold 2erminology

Anticline / conve% in direction of youngest !eds

Syncline / conve% in direction of oldest!eds

Antiform / conve% upward fold

"stratigraphy unknown#Synform / concave upward fold


58/132

Anticline < Antiform?


59/132

SynclineSynform?


60/132

Fold 2erminology

Synformal Anticline / overturned anticline

Antiformal Syncline / overturned syncline


61/132

Fold 2erminology

%onocline / step/like !end in strata


62/132

Foliation and Clea'ageFoliation / parallel alignment of planar fa!ric elements within a

rock

Clea'age / tendency of rock to !reak along planar surfacecleavage is a type of foliation

resem!le fractures !ut are not physical discontinuities


63/132

Foliation and Clea'ageFoliation / parallel alignment of planar fa!ric elements within a

rock

Clea'age / tendency of rock to !reak along planar surfacecleavage is a type of foliation

resem!le fractures !ut are not physical discontinuities


64/132

7ineations

7ineation / su!/parallel to parallel alignment ofelongate linear fa!ric elements in a rock !ody

e'g' slickenlines and grooves on fault plane surface


65/132

Structural analysis

>nvolves three steps

0' $escriptive or geometric analysis

2' inematic analysisB' $ynamic analysis


66/132

-eometrical analysis

*easurement of the B/dimentionalorientation and geometry of geological

structures

simplified into.

lines planes


67/132

lines or linear geological

structures liniation

) any linear feature o!served in a rock or

on a rock surface) any imaginary line ) such as a fold a%is


68/132

rientation of linear

structuresC>1ESTrend ) a6imuth direction measured clockwisefrom north BD;

(lunge ) angle of inclination of line measured fromthe hori6ontal "; / 9;#


69/132

E%amples of linear

structures (rimary ) flute casts7 grooves7 glacial striae Secondary ) slickenlines7 mineral lineations

-lacial striations on !edrock sole marks

http://almandine.geol.wsu.edu/~geo101/sckuehn/Sect3-Sp99/weathering/glacial-striae-chernicoff-cropped.jpg


70/132

E%amples of linear

structures (rimary ) flute casts7 grooves7 glacial striae Secondary ) slickenlines7 mineral lineations

-rooves on fault plane Slickenlines on fault surface


71/132

rientation of Cinear

Structureslinear structures on an other planar

surface.

pitch angle) angle from hori6ontal measured within

the plane(itch

angle Striationson a faultplane


72/132

(lanar -eological Structures

!edding planes and contacts

foliation

@oint surfaces fault planes

fold lim!s

fold a%ial planes "imaginary surface#


73/132

E%amples of (lanar

StructuresBedding planes ) most common

primary depositional surface

erosional surface

inclined !edding plane


74/132

E%amples of (lanar

StructuresFoliation ) cleavage planes produced !y

metamorphism

common in slates and phyllites

foliated phyllite


75/132

E%amples of (lanar

Structures/oint planes 8 planar fracture

surfaces caused !y !rittle failure

E l f l


76/132

E%amples of (lanar

StructuresFold a6ial plane ! imaginary plane

!isecting lim!s of fold

f (l


77/132

rientation of (lanar

StructuresThe attitude of a plane can !eesta!lished from any two lines

contained in the plane7 provided theyare not parallel

f (l


78/132


StructuresStri#e 8 a6imuth direction of a

hori6ontal line in a plane

Dip 8 angle of inclination of line measuredfrom the hori6ontal "; / 9;#

i i f (l


79/132


StructuresAppearent dip) dip measured along

a line other than9; to strike

) apparent dip willalways !e less thanthe true dip angle


80/132

*easurement of orientation

Strike "plane#

Trend "line#

a6imuth orientation measured with a compass


81/132

*easurement of orientation

Strike "plane#Trend "line#

a6imuth orientationmeasured with a compass

$ip "plane#

(lunge "line#inclination measured using

an inclinometer

* f S ik


82/132

*easurement of Strike

$irectionRight hand rule???When your thum! "on your right hand#

is pointing in the direction of strike your fingers are pointing in thedirection of dip


83/132

*easure of $ip Angle

The angle !etween the hori6ontal andthe line or plane


84/132

Structural $ata

Sym!ols represent different structuraldata

Sym!ols are placed on the map.) in the e%act field orientation

) where the data is measured

St d d St t l


85/132

Standard Structural

Sym!oles


86/132

E%ercises

geological maps

structure contour and structure maps

three/point pro!lems cross sections

sterionets


87/132

-eological *aps

distri!ution of rock types andcontacts

) sym!ols on map represent structures"strike and dip7 fold a%es7 faults etc'#

) map and structure sym!ols allow you toinfer su!surface structures


88/132

utcrop patterns

utcrop patterns controlled !yattitude "strike and dip# of !eds and

topographic relief


89/132

GHI Rule

&eds dipping downstream GHI )downstream

&eds dipping upstream GHI ) upstream


90/132

Hertical !eds cut straight

Hertical oriented !eds cut in a straightline regardless of topography


91/132

5ori6ontal !eds

layers always at the same altitude )do 1T dip in any direction

) layered cake


92/132

utcrop (atterns

Which direction are the !eds dipping?


93/132

utcrop (atterns



94/132

utcrop (atterns



95/132

utcrop (atterns



96/132

&lock models

Relations !etween outcrop patterns andsu!surface structures

map view on !ottom ) cross sections in !locks on top


97/132

&ryce B/$ modeling !locks


98/132

Structural +ontour *aps

*ap showing the relief of a su!surfacegeological surface

) top or !ottom of !edding planes7 faultsor folded surface

) constructed from !orehole data


99/132

Structure +ontour *aps

Structure contour lines are lines of e8ual elevation show elevation relative to hori6ontal datum values are often negative since su!surface

elevations are commonly !elow sea level


100/132

$atum Surface

$atum is a hori6ontal referencesurface

regional stratigraphic surface

+onstructing Structural


101/132

+onstructing Structural

+ontours(oints of e8ual elevation along a !ed contact intersection of contact with topo contour

draw structure contours through points of e8ual

elevation


102/132

(lanar surfaces

3niformly dipping plane ) contours areparallel


103/132

folded planar surfaces

+ontours have varia!le spacing


104/132

Rules of +ontouring

0# contours cannot cross or !i/furcate

2# contours cannot end in the middle of the

map7 e%cept at a fault or otherdiscontinuity

B# same contour interval must !e used acrossthe map and elevations must !e la!elled

J# elevation is specified relative to datum"e'g' m a!ove sea level#


105/132

$etermining $ip

$ip direction and angle can !e determined from structureconour maps

measure hori6ontal separation K and find difference in L tan α M L


106/132

Three/point pro!lem

A minimum of three points are re8uiredto uni8uely define the orientation of a

plane


107/132

Three/point pro!lem

Find min and ma%values

$raw line !etween

these and dividedistance into intervals +onnect points of

e8ual elevation Two points in a plane

at the same elevationlie in the line of strike


108/132

Three/point pro!lem

Find min and ma%values

$raw line !etween

these and dividedistance into intervals +onnect points of

e8ual elevation Two points in a plane

at the same elevationlie in the line of strike


109/132

>sochore *ap

$rill hole logs giving the thicknesses in the drilled "oftenvertical# direction

Apparent thickness ) true thickness M perpendicular to

!edding


110/132

>sopach *ap

*ap showing GtrueI thickness measuredperpendicular to !edding


111/132

+ross/sections

+ross/section is a 2/$ slicethrough stratigraphy

construct perpendicular to dip

M true dip constructed at any other

direction M apparent dip

Engineering properties of


112/132

Engineering properties of

faulted or folded rock shear strength) loose materials

) compressive materials) permea!le materials


113/132

hydrology of fault 6ones

water in fault 6ones common due tofractured rock) fault 6one may !e either an a8uifer or an

a8uiclude crushed to gravel

crushed to clay

l l


114/132

hydrology of fault 6ones

water in fault 6ones common due tofractured rock) fault 6one may !e either an a8uifer or an

a8uiclude crushed to gravel

crushed to clay

(ro!lems due to water in


115/132

(ro!lems due to water in

fault 6ones leakage of waste water under a landfill leakage of water under a dam

sudden collapse and inflow of water into atunnel

hydrothermal alteration of rocks to clayminerals along faults ) varia!le physical7

mechanical and hydrological properties solu!le rocks / cavities

f f l


116/132

Activity of faults?

Risk for further movement) active fault ) has moved in the last 0;; ;;; to

B: ;;; years

) dormant fault ) no recorded movement inrecent history

>ndicators of fault


117/132

>ndicators of fault

movement fault scarps stream displacement

sag ponds lineaments vegetation displacement

Ri k i l d d


118/132

Risk potential depends upon.

0' duration of the 8uake

2' intensity of the 8uake

B' recurrence of the 8uake

( i l i ’


119/132

(otential trigger’s

stess N stength

water in a reservoir ) added weight andlu!rication

storage of fluids in old mines

!lasting

surface e%cavation

ground water mined from a8uifers

e%traction of oil and gas from a8uifers

+ di


120/132

+ase studies

Au!urn $am ) wide slender arch dam on theAmerican River7 upstream of Sacramento7+alifornia

Fig' 9'B0 pre investigations

) detailed mapping) O km trenches) 2 km e%ploratory tunnels) B; km !orings

A ! $


121/132

Au!urn $am

geology) metamorphic competent amphy!olite) metasediments) included vertical weak 6ones and lenses of chlorite schist7

talc schist and talcose serpentinites up to B; m wide7aligned with foliation

) series of su! parallel minerali6ed reverse faults with striketransverse to the dam a%is dipping J; to :: degrees intothe a!utment

) two of the longest faults are tangential to the dam7 close orunder the dm on the left a!utment) no active faults in the area) the area was supposed to !e low seismicity

A ! $


122/132

Au!urn $am

foundation construction) earth8uake occurred :'P

) regional fault study) reassessment B2 km trenches more !orings

surface e%cavationsaim to esta!lish the time relationship of

the faults

A ! $


123/132

Au!urn $am

+oncluded that the faults wee formed inanother tectonic setting than the present"compressional rather that e%tensional

stress field#A review of the dam ) will it withstand

vi!rations from a D': magnitude 8uake on afault Q O km from the dam??

Gff setI design recommended to withstand 2:mm to 9;; mm1 $A* !uilt due to discussions on safety

& ld i 5ill i f il d


124/132

&aldwin 5ill reservoir ) failed

09DB 0 principle em!ankment7 JP m

high7 and : smallerem!ankments

e%cavated hollow in !etween atthe top of a mountain range

&aldwin 5ill reservoir ) failed


125/132

09DB

geology) fria!le deposits of the (liocene (ico Formation7 massive !eds

of clayey7 sandy siltstone) (leistocene >ngewood Formation' inter!edded layers of sand7

silt7 and clay7 with some thin linestone !eds= some of thesand and silt !eds are unconsolidated and eroda!le

) &oth formations contain calcareous and limonitic concretions) !edding dips slightly : to P degrees7 striking roughly parallel

to the >nglewood fault

) ma@or active fault7 >nglewood7 passes @ust 0:; m west of thereservoir) the fault is a right lateral strike slip with a vertical

component) fault acts as a su!surface dam for a ma@or oil field in the

hills

& ld i


126/132

&aldwin

E%cavation phase) P minor faults wee mapped

) mostly normal faults) B to 0;; mm silty gouge

) largest fault had a total displacement ofmore than O m

& ld i


127/132

&aldwin

$esign) rock foundation lined with

asphalt and gravel drain layer

covered with compacted clay

covered with asphalt

& ld i


128/132

&aldwin

+onstruction phase 09JP/:0) fault 0 caused pro!lems

) slide initiated revealing that the faultpassed !eneath the inlet


129/132

&aldwin

after completion) liner cracked along the trace of the fault) emptied in 09:P

) cracks repaired) cracks were also o!served in the surrounding area

of the reservoir) the cracks dipped steeply) trend 1S parallel to the faults

) some e%hi!ited small sinkholes ) indicative ofe%tensional strain

) offset dip slip

& ld i


130/132

&aldwin

near!y oil fields ) oil was !eing e%tracted) resulted in su!sidence due to collapse of the a8uifer

) su!sidence of 2'P m !etween 090P and 09D2

& ld in


131/132

&aldwin

Failure 09P0) emptied completely in J hours

) seepage along the fault had enlarged to apipe

) then to a tunnel and

) then the collapse of the roof

) a canyon eroded completely through theall of the reservoir

&aldwin


132/132

&aldwin

Failure 09P0) Why??

cracks in the floor e%tended across the entire

reservoir along the trace of the fault :; mm displacement

open voids along the fault

movement along the fault had fractured the lining

rupture of the asphalt mem!rane water eroded cavities into the foundation rock

Documents

Ch 9 Structures