nome
Homework
3 - SIO160
2- 5T0160
Homework
Duein clsss,next Thursdoy.'
Hereoresomeexercises
to mokeyoucdeptot solving
velocitytriangles.
Mostoresimple,
but o few qretricky. Keepyoureyeonwhotis hoppening
right ot ihe triplejunction.
Monyof ihe velocitytriqnglesinvolveridgesthoi qrelgl spreoding
orihogonolly
to the plotemolion.Thisis notunusuol
onEorth(olihough
not
io lhe exte^t seenin lheseexercises).Thetricky thing in thesecasesis
to the ridgeondis not
ihot the velocitylinetorthe ridgeis porallel
orthogonol
to lhe ploiemotion.seebelowl
i+
<
*l."r,r
--->B
A *--i---- V
j/
ab
Besureto lobelcll velocitylines.
fn problem
ihe lengthof the veclors.
3 youconjust "eye-boll"
Theseproblems
? ol CoxandHort,
orefromChapter
"r
-T
-\l*
I
/\l
nA,+V,^-
I
hasbeencut into threepieces
A pieceof peperlithosphere
A, B, and C in differentwa)'s.In all casesthe paperplates
diagramshon'nat thetop.All of the angles
hale rher,elocity
shos'naremultiplesof 45'.
t+-
,f/\rll I
I
f
-r
.|_
(a) Show*'hetherthe plateboundaries
areridges,trenches,
or transfornrs.
/
'---.-
->l-<
F
1-
(b) Drawa pairof arron'son oppositesidesof eachbound'
arv shori'ingthe directionof relativemotion(note that
to ridgesand
thesearrowsneed not be perpen-dicular
trenches).
1Y
c
AB
-20
a
2a 10
F X . A M P LE
(c) Showrhemagnitude
of the relatirevelocityacrosseach
L ^ ,.^ t- - ,,
vvu l l u d l
G)
A
B
,Lto aa / 3r
c
/-\
r.
B
c
<_
8A
AA
B
c
-->
?
(f)
B
B
B
A
c
c c
B
h\
( ,1
B
A
'
A
B
c
A
c
A
nd/!r
(a)
A
(a)
z_
I
A
A- '_ /r 'r r r r r v)
Hint: If vou have trouble visualizingthe nrotion, hold plate
B fixed and dran'the velocity flelds over platesA and C.
60fry
SOLUTION
B
i^
_l rrl
A
c
The plates are no\!' moving as shon'nbelo*: Proceedas
before.
-4A -2A
'4A
AI BI C
A
,/
t^n\
Blc
'/
n'\$
t
lll
Gt)
c
(f)
A
A
/o\
\D /
B
G)
B
A
A
B
c
c
c
A
c
B
Blc
A
B
(e)
c
A
c
A
5Al^^t5,
Lc )
(t')
(a)
SoLUf t oN
€ (AN\FL E
B
\lake a velocirydiagramfor eachsetof plaresand deternrine
n'herherthedashedboundaryis a ridge,rransform,
or trench;
rhenshowrhe relativevelociryacrossrhe boundar*giving
borh rhe direcrion(smallarron.s)and rhe magnirude(in
units of nrnr/i'r).
u<pdto sh,swthaHhp boundari'is a t-rFsfsFprh,rlft:s_upro
rnu-o-d ererrnlne*belher"ft j+l efplater*l,e**B*t*red
N
8Q
<-ll-a^^,r.
l e aI
I
+
+
qk
A
+
T
te a _ ta
z\z
50
rJ
A
l eo
n tn'
l,/
r\
^J9
-ra+
e
T
c
I
+
\l
L4)
t a6
60 ^^1,1, I
(!,/
+
T
<-ll->
5o
I
--ll*'""t'
t
\.{
0"
s0Luftc.\
-t
+
10 ",^/J.
T
3
)1
A
lbo -ro
^9
rV
/
c
5A
A
10a
+
- Ea
6.\)
\
c
T
T
-tu@-+-
(c )
M
L4J
.l
16
n
A
t3A^^/",
,-
A
I
,"\""
,"\""
\1
,"
c
N
106f
T
Le l
c5a
J /r
CA
A
5a
8
ta ,a -5 e
\oto^
N
tt:
c
T
t,
*/
c
t
5a
tea
--'--t.^
50 ^^/r.
A
| ..,
.i
!{
.n
t^4
'l
+
+
l oaI
qh ,^/t,
trA
3
++-F+rf
T
T,
too -to
56
T
T
T
toa
4) In problem 2, analyzeall of the triple junctionsin velocity spaceto
determineif the triple junctions are stable.If one of the boundariesis a
trench,considerboth casesin which the role of oneof the adjacentpfates
is either overriding or underthrusting.For the stabletriple junctions,
determinethe velocity vectorof the triplejunctionrelaiiveto plate C.
ZA - q*o +;*
'Et
L'u#r'r^
E
-1A -2 A
nr8
,9C
-\a -2a
'-20
:E
nnn
lv
-1a -za
-4A -2A
Lk *t{.^f'U^ \)'M4
-1a -za
-1A -20
'4A
-1 a
-qa
,9
-ra -2a
20
-1a -20
40
47)
-1A -2A
- 4A - 24
1A
/-w
4A
+-qh4-q
l\
2-^ \
)
- ltAta
4A
-4 kt v
-L a
-2a
-4th
tv
-1l_u./
a
'-2A
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