Velocity amI directioD of plate displacemeuts 

by latitude observations 

E. PIW\'ERBIO - Y. Q,UESADA ("') 

Reeeived on January 8th. 1973 

RTASSU'>:'l'O. - Con riferiillento ad 11Il pre{·e{h·nte lavoro ( ~ ) eon il 
quale sono st.ate dedoUe le velol"itil Ili s("onimeuto (lei hloechi Allieriea-
Aumsia elI AllIeri{·a-l'al"ific o, secolHlo la ricost.ruzioue (li Le l'i("hon, 
utilil':l':au(lo la lungfl scrie (70 flnni) ai os;;ervazioni (li lat.itlllliue (Ielle Stal':ioni 
dcl Sl1., gli autori prelulouo in esame il ]Hohlenlfl Ilell 'cfl'e!t.o eh e la indeter -
llIinal':ioue sulla conoscenza llelle coonliuate dei lJOli di rObll':iOllP Ilei hlo('chi, 
lletermiua 8ul calcolo (tella "e!O("itil di ~(·OlTilliento. 

Fal'enllo rÌl'or so lHI un ]lro("eaimento ai ot.tilllizzazione (tei (tati V('u;!"ono 
Ill'terlllinak poi le vcloeitil Ili SCOITiillent.o e le eoonlinat.e 1101 ]1010 Ili rota· 
zioue dei hl o("ehi Am(,TÌl'a·l~umsia. T risultat i si aecon!ano eon quelli 1Il 
pre("edenza Ilet.e\'lllinflti (t ) e risultano nello stesso or dine di gmJl(!ezza di 
(!u(·lli llellotti MI rilcvailleuti g-eolog-iei e ~eofi8ki. 

SU~DtAHY. -- The reslIlts olJt.aine(1 lJy lhe l1utho l'S in a fOl'cgoing 
papc!' ("), IJl"oviding eOn1lJlcte!y indepclI\!ent. evidencc ou the plate tedouie8 
hypothe~is, 11\'(\ IliS('uss('(1. [low lTitÌl'al iH t.he l'llOiec of t1w rotat.ional 
pole lJOsition of t ile platcs is carcfully anfllys('11. 

'l'he ]o("atiou of t.hc ("enhe of rotnt.ion awl the l'ate of rot.ation of 
Allicriea·Elll'flsiu plate has ll<'en sUl"("cssivoly ol, t.ain('(l lly the last ·sr}llfll'e 
fit IlIcthod. 'l'hc8e l'e8 11It.8 al'e in good agl'ccment. with gcophysi('I1\ 1111\! geolo· 
gical moaSIll'elllents anI] ('onfi r lll t.he possibility of using ust.ronOilliefll (lat.fI 
in the stJlIl,l' of ]llak tedonÌl' s . 

INTRODUC'l'lO':-< 

USillg Le Pieh(}]l ~ ~ (!.) rccollstl'llctioll, the .. l . ..ti. (G) comput.ed the 
l'ot.at.ioll rate of thc Eumsia n-Amel'ic a n amI Pacific-AmCl'ican 

(*) lnt.emationfll Lutitude Station, Cagliari, 

" 



2HO B. PROVEIWIO - V. QUESADA 

}llates from m!tronolllical latitudes observed in the five int.ernational 
astronomical ~tations oì 1lizusawa· (Jall:ln), Kitab (USSI{), Ca·rloforte 
(Haly), Gaithersburg a·llI} Ukiah (USA) ~ituated on the + 3H"S' 
}lara11c1. 'l'he data analp!cd cover a period of 70 yea·rs. From t.his 
ana.Jysis it reslùts that in generaI, di~reganling loeal dist.orsions 
whieh undoubt.edIy occur, the Kitab al\(l Carlofortc stations can be 
comiderml as Iying on t.hc Eumsian platc. )Iizusawa al80 lie~ on this 
plate, although close to the boumlary. 'l'Ile fourth amI fiìth st.utions, 
Gait.herslnu·g and Ukiah, must be on diffcrent. plates. Gait.lmrslnu-g 
liCf! near tlw center of tlm American }llat.c a·llI} Ukiah mUf!t be con· 
sidered as llloving with thc East Pacifie plate. 'l'his plate is almost 
cntirely eonS1IDled by t.he ,\merican plate amI onlr a· sma11}Jart remainl>, 
,,·hose lllot.ion if! essent.ially nort.h-west.. 

'l'o deterllline the valuc of the rotation ratc ('h of diffcrcnt lJlatCf! 
(k) by t.he seeuIar vmiations oI the latitude b! oI the stat.ion (i) af! 
well as the sccular motion of the EartHs pole (n), condition equatiolls 
of the tn)e 

[1] 

wcrc used, in whieh thc fIrst. tcrlll of t.hc second member re}H·esents 
t.he eiIect oI sccuiar }lolar motion on obRerve!l latitude variations, 
while t.he second tcrm represent.s the c1feet oI the rotation of the 
station (j) of IOllgit.ude Ai aroullIl the rotation Jlole (k) oì eoordinates 
L k and 1>/: . 

'l'he rcsulting absolute rates of the different })late~, averaged on 
thc ba·sis oì various cases treated (") are Iound to be 

-o" .0037jyear 
±O" .0002 

+0" .00lbjyear 
±O" .0002 

+0" .001Sjycar 
±O" .0002 

(Emasia.n plate) 

(Amcrican pJn.t.e) 

(NB Pacific pla.f.e) 

'l'hcf!c resuIt.s are in cxeclhmt. agreement 1vith thc }llate t.eet.onics 
theorr amI sIlow that Iong-tcrm variations in t.hc motion of tIle f!ta-
tions can be Iound by carehù analyf!is of vcry long serics of astro-
nomical !lat.a. 



YELOCLTY A~D DlRECTION 01" Pr,ATl'~ j)J.~l'L'\CJn!E~TS ETC, 2!J! 

IN'l':EIU,AL A:-ID EXTBRNAL :ElUWRS BY lJB'l':EIDU.:->I.:->G l'OL:E A':->lJ A.:->-

G"CL,\R RATF-S 

The Volar eoordinat.c~ q)~ aniL L I< I whieh arn obtaille!l b:r deLcl' -
mining t.he re lative motions oI dilIerenL }1Ia.Le~, are generali:r alIeet.ed 
by observation errol'S 'whieh lmve rel)ercussions on the determination 
oI t.he absolut.e rates eakula.ted by mea,ns of l'ela.t,ion [IJ. 

The polar eooriLiuates of !liffer ent. }llates are usuall:r ,,~tablishe!l 
clil'ect,]y irom ~})]'efl(lillg rates amI Il'aeLw'e zone azimut.hs (azimuths 
of the t.ramiorm Iaults). In pa.rtieular, the l)ositions oI the ceuter of 
roLa.Lion adOl)ted by I~e Pkhon eJ are obta,ined h om the azimllLhs 
oI the fradure :>;ones. The sLa.ndarcl ~lc-viations oI measlU'ed Irom 
computeiL az imllLhf! given by Le Pichon (2) are ±iJo./ ior the Ameriean-
Padfìe Vole ancl ± 9°.1 ior the Ameriean-Huraf!iflll vo](,. These 
q ult.ntities only indil'edly give an idea of Lhe im}lreeision wit.h 'which 
rot.a,t.ion l)Ole coordinaLns are !letermined. Because oi the l)rocedul'e 
of ('aleulat-ing the eool'!linates oI the pole used by Le Pkhon e), Lhe 
aceul'ae:r oi these coordinates ('all be eOffi}lllLed only "a l)Osteriori". 

From t.he Sl)herieal tl'iallgle (Fig. 1) having as vertices the geo-
graphica.l uorth }lole 1'", t.he rot.at.ion pole l'k of the }1la.Ln (1.:) on whieh 

p. 

S " , 
o 

"o , 
~ 

'" 

a , 
go - a, 

P, "-----d-, -----"--;:A, 

Fig. 1. - Spherical t.rianglo P n l't .AI. 
LO tho Borth geographkal polo and 

'l'he poinh T' ~ anI} l't cOlTPspond 
tho rotat.ion polo o( thc pLì,te. 



2fJ2 E. l'ROV mUllO - V. QUESAlJA 

the point AI, at which the azimuth~ (t, of t.he fracture zone were taken, 
lies, amI the point Ai itself, we ean write the following Sl)herical re-
lations: 

sin rft~ __ o sin rpi t··o~ d, + cos Ti sin di sin (ti 
_~=(4-A,)~_~~~-~.,_"~.' 

e08 (jJ~ 8ill (L~ - }.tl = sin di cos (li 

in which !I(O is t.he allj.çular distance PkAI, whilc ({i(O and Àli) are the 
gcographic coordinates of poillt. Ai. 

From these, ·we can easily obtain 

t.ag rft~ - pos (L~ - }.,) = sec Cf, ~in (L~ - À,) tago (lI 

from whit'h, in tleveloping [uHI ncgleet.ing thc secontl order tcrm, wc 
havc 

cos Cf' cosec (L~ - }.I) (l + tag! (jJ k ) ,1(jJ + 
{ COS CPI - cot (L~ - }.I) tag (t,} ,1L = (l + t.ag! al) ,1al [2] 

By means of this relation it is possible to calcllh1te the tlworetieal 
values of t.he uncertaint.jes .1(jJ ami ,1L of the coortlinates of thc 1"0-
t,atton cent,cr P eorrespunding to the absolut,ell value of the st.·llldal"ll 
rleviat.iolls ,1a, = ±!)o.l of fradure zone azimuths. 

Utilizing the coonlina.tes ami a.zimllths of fradure zones Ai given 
by Le Picholl (2) referring to the center of rotat.ion of the American -
Em'asian plate anrl Sup})()sing .1(jJ = .1L, we obta,in, by formuh1 [2], 
l.1rftl = I.1Lj :::' 20°. 

'rhe~e vahw8, which agree with thc sizes of t.lw elli}J8e of error 
comlmted by Le Pichon (!), repre~ent. the amount oI accuracy to be 
expeet.ed in t.he detennination of the rotation eenter coonlinatcs of 
the Amcrican-EIlI"fl.sian }Jlate from fradure zone azimuths. 

It is illteresting to note that t.lw Vl1hw8 tlms dcterminetl of the 
imIctcrminations of rotation pole coonlinatcs are al80 in agreement 
with the values oI the external })]'ee1sions detcrmine{\ on t.he basis 
of eenter of rot.ation coordinates compllt.erl by difIercnt allthor8. 

In the Jir~t fOlli" lines of 'rable 1, thc valucs of the rotation polc 
coonlillate8 and the relative rate of rot.ation of the Americall-Eurasian 
l)late rleterminel[ by rlitferent author~ are givell. 



VELOUlTY A~D DIRECTIO~ OIo' l'l.ATE DISPLACE~!E~TS ETC. 2D3 

The ,o,tandarll deviatiol1S of t,he eooI'llinates observecl from the 
average givcn in Table l are: 

alo = +lDo 

T [\ b l c l - Rl';).AT!VJ'; VJ~CTOR OF A~IERICA-EIJI,AS!AN PLA'l'E ROTAT!ON 

m I L I 10-
7 dcgirr I Authors 

78"N lO2 oE 2.8 Le Pichon (') 
63°N 137"F, Le l'iehon (~) 
60 0 N l 35°}<; 2.1 ~forgan l') 
48 0 N 155°F, 2.4 Chase (l) 
8u oN 57°,," Pro\'crbio & Qucsada (6) 

}c'rom l'elation [IJ, ncglceting thc errcct of secular polar motion u 
on secular latitude vmiations, for the a,ngula.r rate of the stations 
lying on the America,n-J<JUl'aosia.n pla.te 'we fìnd 

wher€ 

and j = 1,2,3,4 rcfel'fl to 
forte amI Gaitherflburg. 

the rom statiol1s of MillllSf.wa, Kitab, Ca,rlo-
From the foregoing we inmlCcliately finel 

[3] 

"\vhere the coe1ficients A and Bare 

A = [bJ sin r[Jj; sin (Iok - AI)] Llw" - [cos r[Jk cos (Lt - )'I}] LlIo 

B = [sin 2 rPk sin "{L" - ,l,)] i]{P k - [sin 2 (L l' - Ai) CO::;2 W.I..] LlLt 

Utilizillg thc va.llles for ,o,eeubr va.ria.tiollf\ bi (G) a,jHl cOllsidering 
t,he rota,tion center coordÌlmtes (2) we fimI 

(10 -3 see of al'c(yr). 



2!J-1. t:. P1W\'E B BIO - V. QU};S.~j}.~ 

Altllougll thc rcliability of this sollltion is mthcr scarse (sincc 
the computed weight of the quantity L1w is onIy O.OOG) in any case 
we have, keeping in mind the maximum uncertainties in ealclllating 
tllc coor(linates Wl: amI Lk (order of 10 0 ), an uncertainty in tlw com-
puted anguIar mte of thc same rrmgnitwle of the angular rate by 
the .A. A. (fi) determined. 

"\s the {'hoice of ]Jole ]Josition in rotation calculation by means 
of thc cquation [lJ sccms to bc mther criticaI, we {'onsidercd it op-
portune to reconsider the whole llroblem by turning to a difIerent 
criterion of data proeessing. 

DE'l'EIDII'XA'l'IO.:\ 01,' IW'l'ATIOK CE~TER A'XD RATE F1W11 AWl'IWK01IICAL 

LATI'lTDES 

'rhe loeation of the center of rotation amI thc l'ate of rotation 
of thc American-Ellraf\ian plate \Vas dctermined by t.he lea.st.-squal'e 
fit mcthod, similar to the onc med hy l,e Pichon for the determination 
of l'otation parametel's of rigid hlock8. 

Thc numcricaImethQ(1 of litting minimizcs the 8um of the squares 
or the sbndard deviations of the residuals 

(i = 1,2,3,4) 

between the observed values of secutar lat.it.ude varia.tions a.ml those 
ealelllatc(l by t.he expression [l]. 'ro calcuIate this expression, the 
fìxed pammeters n = O" .0030 amI v = GDo.G, detcrmincd b'y the A.A. (~) 
with sufficient accumey, which clmracterizc the secuiar motion of 
thc EaI'th llole, \Vere introduced. 

The valucs of boa l \Vere t.hcr!!fol'c calcllbt.wl by means of [1] as 
a fUllCtiOll of the pa.ra.tneter Wk, changing thc coonlinatcf\ Wl: alld Lk 
by steps of fìve degrucs over the range 

o ~ W", ~ 85 0 
O ~ L" ~ :155" 

The values of t.he stalHlanl duviation 

ak.m ... (Wk, W." L.) = ILlc/ 1 'I, 
• ( m,JI 

(i = 1,2,3,4) [41 

are plot.ted in diJIel'ent diagrams .. As a11 example, in Fig. 2 we reprcscnt 
the valncs of ak,m,!!, corref\ponding to W l: = ± 0".0012, with the plus 



-, 
l a 

aB 

06 

04 

(5 1\.n 

ep . o' 
ep .lO" 
ep ' 20' 
ep ' 30' 

ep ' 40' 

ep . 50· 

ep . 5 0 · 

02-

00 
, 

O· 50' 100" 200" 250· 300' 350· 
l"i~. 2. - R c p l'Cllcn t n t.inll nf the valu(' 8 (lf t,h o st ll llllanl lIeviatioll (J" t ,," , .. C(ll'!'(lS}IOlH ling to w~ = ± ()".{)0 12, wit.h 
t,ho po~i t i vo Sig ll l'd cn ing LO llIot,ion o{ th ~ .A lIl cl'k all pl il t.c ;\1\(1 n ega t iv e 5i~1l l o llI ot.i on of i lio E u r;l si illl p la t e. 



2!)fj E. l'ROV.I!H BIO - V. QUE.~ADA 

sign l'cIerring' tu mution of t.he Americfl.ll blocIe ((::aithcl'sb1ll'g ~tfl.tion) 
and the minus sign to motion uf thtl Ellra~ia,n bIocIe (llIiZUf!'''Wll, Kit,ab, 
Carlofurte stat,iuns). 1<'ur par~h {!le value we thus obtain a, curvp rtl-
prcscnt.ing' a n abwllltc minimmll of t.he stalldanl dcviation in cor-
rpspondence t.o a determined pail' of W." Ln valups. 

Oli the ot,IHlr lmnd, ill l<'ig. :{ wc fina the ClLl'VPf! of tlIP absoIutf, 
minima uf the HtfHHlm·a arwil"tion a" k ,m a.s a Iunction of latitwlp Ln 
cOl'l'esponding to the va.Iucs oI W k and rfJ/n given in Table 2. 

Tahle 2 

Cude 
I 

± Wk 
I 

~, 
(0".001) 

( l) ± 12 -:- 75° 
12 

(2) ± " + 8(]o 14 
(3) ± 16 , 800 

16 
(4) ± 12 + 8 ll" 

20 
(5) ± 15 + 85° 

35 
(H) ± 12 -, 85° 

50 
(7) - 12 + 85° 

O 

Ana,loguuH CUl'VCH a,re given in Fig. -i. Thc latteI' wpm caIclùatell 
keeping t.he parameter rfJ k = 820 COllsta,nt a,nd va.rying tlHl vahIPS 
of Oh, ,1..<; avppal'H [1'om 'l'able 3. 

Tu.ble ::I 

Code I :l: Wk (0".001) 
( l) O 

- 30 
(2) + 5 

- 30 
(3) + lO 

- 30 



0: 0 

o 

6 

4 

1 

2 

.1 

.6 2 
~ __________ 77~~------------__ ~7~ __________ ~~~4 

'5 

gO 180 270 3 60 
l 'il:(. 3. _ D ingmlll of thc cu rvcs 0 1 tho aboolutR mi nim a o f t lu; s(.fi Il.~1an) deviatiOli a~." :lS a hlllf' tion 0 1 

la.ti tud c C~ eorrcspOll ù ing to !.ho \'alucs oI Wl; ::m d 'P", givcn in T ahle 2-. 



2G8 E. rnOVlmBIO - Y. QUESADA 

cr 
0,12 

0,10 

0 ,08 

0,06 

0,04 

0,02 

(1) W (Glo) ~ 0 .0000 
(~w (Gao)- 0.0005 
(3) w (6 .. ) :0.0010 

3 

À 
O,OOL~--~o---?O--~o---..,--",o--'",---"'--,,,,--~, O 10 20 30 40 50 60 70 80 90 

Fig. 4. - niflgram of the cm·ves of siamlanl devifltion ('aleulatc(l by kceping 
thc pamlllctcr <P~ = 820 {·onstant am] varying thc valnes or ili" as appears 

from Tablc 3. 



ygl.OCl'l'l' A:'O nIRECTlOX OF PLATE DIEPL\CE)fKKTE ETC. 2\)(1 

Fl'Om the avemge of the values alm antl L o ohtaùwtl by nllui-
rrUzing thc sta·ntlartl deviations in the variou,~ cascs, thc follow ing 
va.lucs Ior the rotation ccntcl' eoordinates of the .\merican-Eurusian 
pla.t.c were obt,ained: 

The avera.gctl value oi thc rotation eeuter eool'dinates obtainetl 
by Lc Piehon a,nd other authors by utiliziug spre:Hling rates and 
a zimuth oi the trausfOl'ln f:mlts given in Table 1 is, on t.llC othcl' h a utl, 
al = G2"N, L = 132°B, 

Comparison oI t.lte v alues oI these latt.cl' eo{mliuateR to those 
'we calClùated sho,'rS that the two l'otat,ion cent,ers are situatctl ap-
proximately ou the sa.me mel'idian lmt ou opposite sidcs 'with respeet 
to the E:u'th rotatiou polc. 

'r he vahwR wc fountl Ior thc eoortlina.t,cs alI: antl L k a·re, iu a.ny 
ca.sc, i nchLCletl within the ellipse oI crror given by Lc Pichon (2). This 
ra,thel' cornforting result once again demonst,mtes t,he possihilities of 
a.fìt.ronomical d ata iu st1HlieR ou the sceuhu motion of thc Eal' th's el' usL. 

Iu Big. 5 we filllI re]lrescutctl in a diagram t.llC valucs oi the st,an-
tla.l'tl tlevi ations a l: corresponding to t.lle values <PI: = 82o~ a·nd 
L I: = mo\V anel ca.}culateel h y keeping fixwl thc va.luc 01 angular 
veloeit,y (JJ t I 2 ) = + 0".0012 of thc Amcrica.n p lat-c a,nel changing the 
va.1uc (ù k I 1 ) (hav iug a· minus sign) oI t.lle angtùfH veloeity of the sta.tions 
oi the Eurasi a n plate. 

]<~l'om the cmve interpolatetl from J!~ig. 5 i t- is seen tlmt the most 
prolmhle value fol' a.ugul: u vclocit,y of thc Eurasian plate seemR to be 

W k (1 ) = - O".00295jyear. 

Successively using this valuc and varying the value of O.lt 121 , 
the m iuimum values of sta.nclarcl eleviatious relativc to t-he various 
valucs 01 Ol k (2) introtluccd 'were cletel'lniuctl. 

Tn Fig. 6 the tremI of thc values oI W j; ( 2 ) a·rc l'cpresentecl. 
'fhe curve presents a m inilllmll in cOl'l'espoJl(lcnee to the value 
Wk (~) = + 0".00125 . This value cali be consiclcrecl as being thc most-
praba.blc for thc rota.t.ion speetl of thc U .S. Amel'iCil-n plat-c. 

It is most int,erestiug to observe t,hat the most pl'ob able v alues 
of the fUl!:,'1llar veloeiticR 



2.0 . 

1,5 . 

1,0 . 

0,5 . 

O 

aoo E. PHOVE II BIO - Y. QUESADA 

(1),,1 1 ) = - 0".00295 (Emaflian plate) 
(0,,(2) = + O" .00125 ( .. A.lllel'ican plate) 

are in exeellenl agreclllent witll those obtaincd by an entircly imlepeud-
cnt. way ( ~ ) and rC]lorted in the inll'oduction oi this llHol)er. 

The optimization melhod lL~ed in tllis paper is efficacioUf\ in t.lle 
hypolheflifl t.hat lhc nUlllbcr of residuals .d<p ! is greater than L This 
llas allowcd t.he determiImtion, as wc have seen, oI f.lle most llTob-

0', •. <> 

• 

.;-

_<..:1:1) 

l O 20 30 40 50 

l"ig. 5. - Diagmm of tl\C valucs or thc 
sbmIard dcviation corrcsponding to 
thc valucs <P" = 820N and L" '=-' 570 W 
and cakuIa.tcd by kecping nxerl thc 
value or angular vclO(~ity or the 
Arncrican platc antl changing thc 

value or thc Eurasian platc. 

0'" "" 

40 

35 . 

30 

25 
5 lO 15 20 25 

Pig. 6. - Hcprcscntation or thc trenll 
o[ thc valncs of W,, {l). T he eurvc 
prcscnts a rninimum in corrispondence 

tu the valuc W,,(I) + 0".00125. 

u::/.2 ) 

30 



VISLOCITY A~D DIRECTIO'\ 01" PLATI, nISPLACE~m"TS ISTC, 301 

able values of rot.a.t.iun cent.er coor(lin ates and or angulal' vclocities 
Wt relative t.o the two ~\merican and EurHsian blocks, 

In the case or the SE l'acific plate, we have only une value or 
the quantities L11fi, COlTeSl)OlHIing to the Ukiah sta.t.ion (U,S,A,), In 
this circulllst.ance it. is tlms comllletrly imVossible t o obtain minima 
fuI' the sta,1lI1anl errOl'S a, However, it is possible even in this case 
to carry out an llnalysis of lllll'rly qualitative interest by !lctcrmining 
the m,nge of variability of the Varametel'S fJJ, L and (J) which annuI 
t.he resi!luals: 

[5J 

In Fig. 7, in boM-faced type, the area,s of variabiIity of t.lw pa.I'lk 
llleters W, L and w am rcpresented, for which the lH'evious condition 

o 40 80 120 O 30 80 90 

10 
~ 

li 10 
h 

Cf 

14 I \ 
/ \ \ 

14 

18 I 8 
22 22 

w \ w 
Fig. 7. - Rcpl'cscntatioll of thc a.I'CllS of variability thc ]Htl'amctCl's 'J;, 
J, ]l!atc, all,I w rorrespolldill.!; tll thc lllotion of thc Amcrica.·Pacific. 

is actually veril1cIl. \Ve consider it most significant. that also in this 
case the values of the rotation center C'OOl'dinatcs of t.hc American-
l'aC'ilic vIat.e Iletel'mincil by Lc Pichon (2): rp = 530~, L = 47 o W, 
cleal'ly indicatcIl in the sn,me F ifi. 7, fall within the areas or variability 
which, in a sense, repmsent t1w optimal areas of t.lw values of the 
parameters cf> alHl L. 



302 E. rnOVl;; H JlIO - V. QUESAVA 

CO::-;-CLlJSIO::'\S 

To (;onelude: 

a) ll.~ing a lH'oee!lu1'e completely ilU1epcndcnt or the one used 
by .A. A. (G), the most llrobable value~ oi thc cool'(lina,tes a,nd veloeity 
oi l'Otation of the America.ll-Bnrasian plate wel'e determined; 

b) thefIC vailles are in full agreement with tllO.~e lH'eviomly 
!lcterrnine(1 by A. A. (") and a,re on the sante o1'l1er a,i'! those ca,lcuIated 
with geophysicul alHI geological measul'ernenti'!; 

cl this connrms the possibility of ming astronomical (la.t.itude 
a,llIl longitn!le) obseryation !lata ill the stn!lr oi the secular motion 
oI thc Earth'.~ Cl'Uflt. 

REFEREKCES 

(1) ClIASl~ C. G., 1!J72. - TIIC N. Pla/.c prol!lcm 01 plale tec/ollics. "Geoph. 
J. R. AstI'. Soc..", 29, pp. ll7·122. 

(2) L}~ PIClION X., 1068. - Seu·F!ool' Sln'ea~ling allil contilUJntal drijt. 
"J.G.R.",73, 12, pp. 3(iul·3U97. 

(3) LE PICIIO:S X. anti Fox P. J., 1071a. - Jlargina,! Offse/s, Frac/ltrC ZOI . CS, 
and 7:J'arly Openi),g oj t/te NO/,t" A.tlantic. "J.C.R.", 76, 2ij, IIp. 62!J4· 
6308. 

(~) LE 1'lCllON X., HJ7l. In press (private communicn.tion by Dr. 
J. Frn.nchcten.u). 

(~) ~loJ\GA:S J., Hl7!. - In press (private communicn.tion by Dr. J. Fran· 
chetcn.u). 

(' ) PRovlmmo E. and QUl'-SADA V., 1!J72. - Analysis o{ sccnlar polar motion 
and contincntal {lrift. In presso "Bull. Ccod.".