ML20105A732

From kanterella
Jump to navigation Jump to search
Transmits Draft Article Proposing New Kinematic Model for Southern California.Article Hypothesizes Zone of Active Deformation Including Western Transverse Ranges.Related Correspondence
ML20105A732
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 12/14/1984
From: Crane P
PACIFIC GAS & ELECTRIC CO.
To: Asselstine J, Bernthal F, Palladino N
NRC COMMISSION (OCM)
References
CON-#185-656 ALAB-782, OL, NUDOCS 8502040479
Download: ML20105A732 (34)
v • d • e


Text

e- -

I QEyTED CORRESPopounct

,}

  • --ru i
c. nt,tr h%AC PACIFIC GAS AND E LE C T RIC C O M PANY AN FR ANCISCO, CALIFORNI A 94106 T ELEPHONE (415) 781 4211 g 77 % A [ $7 pggg i

I P. O. BOX 7 4 4 2, S A N FRANCISCO, CALIFORNI A 94120 TE LECOPIE R (415) 543 7813 0F F[r: n; u p. ;h,j 6g 6. n.,.,,.,.,

g y{g f.p3 ,.,.,.,.;.,.y.... g.,.,..,,... ..g.,,..,,.,.,. ~ aosanv onLeAcn v.ca e.cuem.. er.su6.no..., gg4ggg - gg,.gg. yg ;yg.. f,=73;.,.;o .g 7.,,.,g., ii.;'ls* = *?.'~"

  • ..*nt'""
=7: ',;;.*:.*.*.
n'.*i*::: :""
L*.'s**::"*

?.2" *i ir"* ~;*:' "a*::.* * %?:*. :::' uti:: =:......

.:.r"::...
=~.* an...
= c.:: n?.....
= #..*::'.*..'*'

lL7.* *C::~." "!/.*:.'.*c.".:;0*" . :... f,*n'

== ':=:. "

==::."== '*

=.::':.=
=:.:= ""

in;.;;*r=...

-::.:.'r....
= citat:" r
r. tt:--'**

December 14, 1984 Chairman Nunzio J. Palladino Commissioner James K. Asselstine Commissioner Frederick M. Bernthal Commissioner Thomas M. Roberts Commissioner Lando W. Zech, Jr. US Nuclear Regulatory Commission 1717 H Street NW Washington DC 20555 1 Re: Docket No. 50-275 Docket No. 50-323 Diablo Canyon Units 1 and 2 Gentlemen: Enclosed for your information is a copy of a-recent draft article prepared by two doctoral candidates at the California Institute of Technology proposing a new kinematic model for southern California. The article hypothesizes that there is a zone of active deformation-in southern California which is interpreted to include the Western Transverse Ranges and northwest trending, predominantly strike-slip faults close to the coast north and south of the Transverse Ranges. Included among these faults is the Hosgri Fault. According to the article strain on this system is thought to account for about a third of the total North America-Pacific Plate motion. We are reporting the article to you at this time in view of'the motion pending before you to review ALAB-782. We remain confident that the seismic design of the Diablo Canyon facility is conservative and appropriate for ?? 479 041214 By20 ONDENCE PDR upcc bORRE Sal

1 S -6 Chairman and Commissioners December 14, 1984 US Nuclear Regulatory Commission Page 2 the seismic conditions of the area. As with other papers and articles which have been published since the conclusion of the seismic hearings in February 1979, we and our consultants will continue to monitor and evaluate this article and others which may follow as a part of the Company's Long Term Seismic Program. Very truly yours, /s/ Philip A. Crane, Jr. PHILIP A. CRANE, JR. PAC:nl Enclosure cc w/ encl: Judge Thomas Moore Judge W. R. Johnson L. J.' Chandler D. G. Eisenhut G. W. Knighton John B. Martin H._E. Schierling Service List

REL ~' '~'AT59 NE55!ygg; ' :qqn v %k; I A Kinernstic Model of Southern California i '84 GC 17 P2:53 8 8 and Gene Humphreys ggg,, Ray Weldon Division of Earth and Planetary Sciences DOCKOk[usN. r UNANCh California Institute of Technology Pasadena. CA 91125 Abstract. We propose a new kinemaut model for southern California based en late Quaternary slip rates and orientauens of maj,or faults in the region. katernaDy sonsistent mouans are calculated assuming that these faults bound rigid bleeks. Relauwe to North America, most of Californiawest of the San Andreas Phult is moving parallel to the San Andreas Fault in the big bend reglen, and - mot parallel to the anoUon of the Pac 18e Plate. This is accessplished by retauen of southern California around the big band, and by the westward movement of ~ eentral California. north of the Garlock Phalt. The velocity Seld astribution in ~ southern California is salculated along several paths that begin in the Mojave Desert and and ett the Califemia seest. 'A path that erosses the western l 1-. l Wansverse Ennges accumulates the accepted relattre North AmericafaciSe Plate velocity whue paths to the ' north and south suggest a signiseant missing esmponent of neuen. These results haply the existenes of a sene of asuve deformauen la southern California which is laterpreted to laelade the western hansverse Ranges and NW trending, predanniana.ly strikes!!p faults eloos to the seast north and south of the Transverse Ranges. Strain en this system is thiogght to account for about a third of the total North Americafaelse Plate sneuen. i. l 3 Um: sed mutas cestegime* sarveyroeside r.e2 conese 8 Umwerstsy at Cassernia.kverside i

.n. i i l Introducuen Southern California is a tectonically active region, experiencing continental rifung, transform faulting, and small-ecale collision. The forces that drive these f processes are only partially understood, and despite a great deal of work even fundEnental aspects of the kinemaues are being debated. In this paper we have t i modeled the regional displacement Seld across southern California using avall-able Quaternary ally rates for major faults. We propose a kinematic model that diSers signiscantly from those presenuy pubibbed in the literat,ure. We begin with the observation that little' convergence occurs seress the portion of the San Andreas Fault between the two bends of the big bendi (Figure 1). We use new data that indicate that the total shear rate between cratonic North America and 4 the Pac 1Sc coastline is inadequate to account for the relauve Paciac-North American Plate motion. Using the slip rates and trends of the major faults in southern California (Figures 1 and 2) we conclude that most of California west of the San Andreas Fault is moving parallel to the San Andreas Fault in the big i bend region, and not parallel to the Pac 1Sc Plate mouon or to the San An'dreas i Fault north of the big bond. Furthermore, major ossbore right lateral faulting with a signiScant component of convergence is necessary.across KY trending ~ faults to account for the sup rates and trends of the major faults in California. i Problems with Previous Kinemaue Nodots The present tectonic regime is usually modeled with southern California attached to the Pac 1Sc Plate and moving about K35W relauve to North America (e.g.. Atwater.1970; Anderson 1971; N111.1952; Bird and Rosenstock 1984). This motion is roughly parallel to the section of the San' Andreas Fault north and The terz 'h;a knd* As used to refer to the seessen er the sen And eas Fauh that s=.esde 3 aber. We58 in the Transee-se Ranges regies. k hes kiseen the 'merth bend' and the 'sw.r.h 1 bend *, two sargs changes in the trend et the San And eas Fauh. d j >h ,4.. b -.N N avere m e

n 3-south of the big bend. The Transverse Ranges, which span the big bend region, are commonly attributed to compression in a zone of collision between the I Pacioc and North American Plates. Several serious problems with this interpre-J tauon are discussed below. l')' The net shear strain rate across southern California, determined from i recently estimated slip rates on southern California faults, does not add up to the relauve Pacioc North American plate velocity (Weldon and Sieh,6: press; Sieb and Jahns,1984). By our estimate, one third of the total plate velocity of 56 l 4 mm/yr (Minster and Jordan,1978; 1954) is presenUy not ac' counted for by major onsbore faults in southern California. Other workers (e.g., Bird and Rosenstock, 1954) have addressed the problem of total slip rate across southern California, and have pinduced solutions that yield the relauve Pacisc-Korth American Plate motion. Recent information on the slip rates of the southern San Andreas fault, (Weldon and Sieb, in press) and the San Jacinto Tault (Sharp.1951), however, j constrains each of these rates to be about 10 mm/yr'less than previously ( thought. These slip rates, and the rates of the other' major faults in southern California that are considered in our model, are shown in Figurs E.

2) A mass balance problem exists if southern California is moving with the Paelse Plate b cause the direcuan of mouon would require a tremendous amount of convergence in the big bend region. A 'almple calculauon for the amount of crust that would have encountered the big bend can be made. The width of the coulsion zone-(normal to the relauwe plate motions) is about 150 km. and the amount of convergence is assumed to be equal to the offset on the San Andreas Tault, about 300 km. Using a crustal thickness of 25 kmla volume of crust greater than one million km has to be accounted for. An unusually thin 8

crust or a progressively widening big bend might reduce this' volume, but it seems likely that at least one-half ml!11on cuble kilometers would have been .E N Y \\sm

.o. cons.umed if this convergence occurred. Volume esumates that include crustal thickening, east-west extension, material transport through erosion and depost-tion, and crustal" flow" around the big bend have been estimated to be less than a quarter million cubic kilometers (Humphreys.1984). b) There is little geologic support for large scale Quaternary convergence in the central Transverse Ranges, and what convergence there is can be attributed to the local geometry of the fault system (Weldon.1964a). If California south of the Transverse Ranges were moving with the Pacific Plate, at least 20 mm/yr of convergence would have to occur"everywhere across the Transverse Ranges. Most of the convergence across the central Transverse Ranges occurs on the l Sierra Madre-Cucamonga Fault system (Figure 1). However, acuvity here is thought to vary between 1 and 6 mm/yr (Ziony and Yerkes.1984) and this is the i only structure upon which a significant amount of Quaternary shortening has been found. In the eastern Transverst. Ranges considerable convergence can be assigned to the Banning strand of the San Andreas Fault (Matu et aL.1964). Between these two regions of thrusung lies m'secuan of the San Andreas Fault 50 l km in length along which litus or no convergence can be documented (Figure 1). Despite loca1 northeast dips of the San Andreas Tault in the arwa features oSset by the fault can be restored by pure strike slip mouon (Weldon, unpublished mapping). In fact, extension is locally taking place on faults north (Weldon. 1984a) and south (Matu et at.1984) of the San Andreas Fault in this area. It is impossible to appeal to simple northwest-directed collision between the North American and Pacific Plates to explain the Banning and Cucamonga thrusts without also having major convergence between them. Other geologic observauons constrain the amount of convergence that has occurred across the Sierra Madre-Cucamonga and San Andreas Fault systems. The recogniuon of proximal early Pleistocene and late Pliocene sedirnents o -"--------.m-..m

  • '1 5-derived from the San Gabriel Mountains, both to the north (Barrows 1979; Foster.1980; Weldon,1964b) and south (Matti and Morton.1975: Morten and Matti 1979) of these range bounding faults rules out large amounts of conver-gence. The detalled match of bedrock terranes, Tertiary deposits and early Cenorpic' structures across the San Andreas Fault zone in the Transverse Ranges (e.g., Ehlig.1981: Ehlig et al.,1975; Crowell,1981: Silver.1982: Powell 1951) argues strongly against ".:onsumption" of signi!icant volumes of material across the San Andreas Fault in the central and eastern Transverse Ranges since at least the Miocene.

l

4) It is physically difficult to understand how signiacant motion could occur on the southern San Andreas Fault if the material south of the big bend is mov-ing parallel to the secuons of the San Andreas Fault to the north and south of the big bend. The big band fornis an impediment to the northwestward tran-sport of southern California, producing a situation in which other crustal frac-

~ \\ tures are more favorably aligned to accommodate the shearing motion (e.g., the San Jacinto and Elsinore Faults). Using a Snite element method, KosloS (1978) modeled the southern California crust as elastic blocks separated by relatively teak viscous faults. Then driven by a far Seld shear oriented so as to drive NW edirected right-lateral shear. he could not produce an acuve southern San Andreas Fault because the more favorably located faults relieved the stress. Kosloff (1978) and Humphreys and Hager (1954) have used this as evidence that l the manue must be contribuung forces that drive the southern California crust towards the Transverse Ranges. With this new kinematic model, however, the magnitude of these forces are reduced.

5) Trilateration, strain measurements (Savage 1983) indicate nearly pure strike-slip motion occurring along the length of the San Andreas Fault in south-i ern California. These data indicate that the strain Seld remains non convergent I

l -s-and rotates by the amount needed to keep it aligned with the local trend of the San Andreas Fault. The priiscipal strain axes across the three southern Califor-nian networks are shown in Figure 2. The lack of convergence is particularly striking in the central Transverse Ranges where the greatest amount of N-S strain, accumulation would be predipted by existing models. Overall, the evidence does not support Quaternary compression or geologic convergence in the central and eastern Transverse Ranges of large enough mag-mitude to be consistent witin the current models of NW-directed motion of material south of the big band. Local convergence does occur, but it can be attributed to either abrupt changes in fault trends or juncUons between major i faults. In fact, serious problems with tbs geology and the geodetic data arise if l major regional convergence is assumed during the last few million years. i e The proposed model has two major new features. First, we suggest that the l material between the big bend and the Paci8e Coast is moving around the big bend by rotating in a counter clockwise direcuon about a pole located approxi-mately 650 km SY of the San Andreas Fault in the big bend region. This rotation allows movement along the San Andreas Fault to be strike-alip both in the Salton bough and in the big bend (Figure 2), in agreement with the strain data of Savage (1963) and the geology discussed above. Note that except for a small step in the trend of the San Andreas Tault near the south bend, the San Andreas Fault Sts remarkably well on a circular are with its center at the proposed pole poeition. From the Salton Trough to the north end of the big bend. a distance of 400 km where we believe this rotation to be occurring. there are no deviations from the are greater than three km other than the step at the Banning Tault. Furthermore. the velocity Seld presented by Savage (1983) for the trilateration l

. =r. 1 network across the Salton Trough is itself suggestive of rotauon about a pole i located in approximately the predicted position (Figure 2). 'Ibe second. feature of our modelis that a algnificant amount of fault activity is taking place in southern California west of the Elsinore Fault. If the slip is occurring on hT trending faults like the Newport-Inglewood or other oEshore faults, about to mm/yr of right lateral slip and 5 mm/yr of normal convergence l is required. Other authors have proposed rela'tively large amounts of slip offshore (e.g., Anderson.197h a 10 mm/yr) but our model is the Srst to integrate it into a complete de'scription of the plate boundary. i ~ 4 A convenient way to test the internal consistency of this model is to per-f form line integrals of the strain rate between points of interest. If this is done between points on the stable North America Plate and the Pacific Plate, the total relative plate motion abould be accumulated. This niethod has been described l-. by Minster and Jordan (1954) and applied to a path across the Great Basin and central California. If au of the modon along any chosen path is considered, the results are independent of the path, and different paths connecting the same end points will yield the same results. We have considered the four paths shown on figure 3. Then the path over which the integrauon is carried out encounters no rotauon or distributed defor-mation of the blocks, the integral reduces to a simple sum of the relauwe slip rate vectors across each velocity discontinuity, generally a fault. Paths 1 and 2 have been integrated in this manner. Paths 3 and 4, which cross blocks rotaung on a relatively small arc, requires accounting for continuous modon. For simpli-city the overall defornjauon in the western Transverse Ranaes is treated as though it were a single thrust fault parallel to the trend of the major faults and l folds in the area. The effects of errors in the slip rates are discussed separately in the next secuen. 4

1 .g. t I I. The paths begin in the Mojave Descrt, which we believe is essentially part of I the North American Plate. 'There are two reasons that lead us to believe that this is true. A path from cratonic North America to the Mojave Desert can be constructed south of the Crest Basin that crosses very litue signl8 cant Quater-naryjeformation (Y1gure 3). Also, there is recent evidence (Weldon et al.,1964; i Dokka.1983) that the Mojave region has not experienced the significant late Cenozoic rotations or deformations C t most previous models hypothesising an l i active Mojave require. Garfunkel

6) and Calderone and Buuer (1984) have proposed large scale counter-clockwise rotations, and Luyendyk et al. (1950) and Bird and Rosenstock (1984) have proposed large scale clockwise rotauons within the Mojave Block, accompanied by major shear on the many hT trending faults that exist in the region. However. Dokka (1983) has demonstrated that i

these faults have not experienced enough total displacement to signincanuy deform the Mojave, and Weldon et al. (1954) have demonstrated paleomagneti-J cally that the SW Mojave has rotated less than 4' since the middle Miocene. If l the Mojave has not experienced sign 18 cant internal deformauon or rotauon j since the Miocene. and there is no major Quaternary structure separating it I from North America, we feel that it can be considered a part of the North Ameri-een Plate. Path 1 begins by crossing the Cariock Fault and continues onto the Sierra block. We assume that the trend of the Carlock Fault west of the Owens Valley Tault (i.e., west of the Crest Basin) indicates'the direcuon of motion. SSSW. and that the slip rate is 11 mm/yr (the best estimate of Carter.1980; 1962). There is considerable uncertainty in the slip rate ascribed to the Carlock Fault, which will be addressed below. Though uncertainty exists. Carter's estimate provides the best constraint available today. From here the path heads west and crosses the San Andreas Fault, which contributes 'a vector parallel to the trend of the -.. -.. -....-.-.j_-.-_..-_-=--===--. - :-. = ~ - ~~ ~ ~ :.L

t 9-j 1 San Andreas Fault (N40W) with a magnitude of 35 mm/yr (Sieb and Jahns,1984). ~ I This results in a vector for'the Salinta block (relative to North America) of 38 mm/yr that is directed N58W. This leaves a discrepancy of 23 mm/yr oriented l NSW that is needed to bring the the not motion up to that of the Pacific Plate. f The discrepancy vector is shown in Mgure 3 n 4 " hollow" vector located at the i i end of path 1. The discrepancy vector is similar to the preferred discrepancy velocity vector of Minster and Jordan (1984), though our discrepancy vector ~ predicts slightly more convergence in the region west of the San Andreas Tault i as a result of the more southerly drift of the Sierra block in our model. As noted by Minster and Jordan (1964), much of the discrepancy vector may be taken up 4 on the San Gregorio-Eosgri Tault system, and there is geologic support for this. Weber and Lajoie (1977) suggest a rate of 6-13 mm/yr of right-laterdi slip for the fault, and Crouch et al. (1954) present evidence for considerable convergence across'this and other faults west of tie San Andreas Fault-r. Path I follows path 1 across the Garlock and San Andreas Faults and then F 1 's south through the western Transverse Ranges to the o a ore area. Yeats 'fh ~ (1953) calculates a rate of convergence across the Ventura Basin of 23 mm/yr i for the last 200.000 years. More recent unpublished results from this area also l give a high, though somewhat lesser rate of convergence (Rockwell. 1963: 17 t 4 mm/yr). It is not yet known how the rate varies across the province or whether i the numbers represent the total western hansverse Ranges. We have chosen to use Yeat's value, and we infer a direction of NSW. normal to the major faults and j folds in the area (Maure 2). Path I results in a relauwe motion (55 mm/yr. N35W) indisur.guishable from that of the Pac!Ac Plate (as shown in Figure 3), suggesting that the borderland south of the western Transverse Ranges is mov-ing with the Paciac Plate. e--s ~,- ey.,,_....-, ,w,-w.evw,,_ $%._-.m,- mn _m,-%m--,-w.e h

Path 3 crosses the San Andreas Fault east of the junction with the San 4 Jacinto Fault and' enters the Salton block, picking up a velocity of 25 mm/yr (Weldon and Sieb iln press) directed N55W. which is parallel to the tangent of the are St to the San Andreas Fault where path 3 crosses it. From here the path l turns'-SW and heads direcuy towards the pole of rotation. By heading in this t direction the only effect of block rotation is to decrease the magnitude of the velocity vector linearly in such a manner as to attain a value of zero at the pole. The faults that are encountered along the path are treated as translations that 4 ' supply velocity wetors that are simply superimposed to determine a net slip rate for any point along the path. Path 3 crosses the San Jacinto Fault, picking up 10 mm/yr (the long term Quaternary slip rate of Sharp.1951) directed paral-I nel to the fault (N47W) and the San Andreas component decreases by 1.5 mm/yr due to the appt oach of the pole.* This results in a velocity vector for the Pomona block of 33 mm/yr oriented N52W. Continuing to the SW the Elsinore Fault is erossed next, adding about 2 mm/yr (constraints on this number are discussed i in the next section) of right-lateral moUon oriented N49W. and passes onto the Ims Angeles block. Subtracting an additional 1.5 mm/yr from the San Andreas component of motion for the continued approach towards the pole yields a velo-city wetor of 33 mm/yr directed N33Y. The path is Anally brought offshore and - another 2 mm/yr is removed from the San Andreas component. yielding a not relative wlocity vector of 32 mm/yr pointing N50W..The discrepancy vector at the terminus of path 3 is indicated in Figure 3 with a " hollow" arrow that is 25 mm/yr pointing N11W. If path 3 were to be continued to the terminus of path I a velocity vector would have to be included that nulls the discrepancy vector, implying the existence of a sone of signincent destral shear strain occurring between the Los Angeles block and the end'of path 3. As the north-south directed compressive

11 deformation in the western, Transverse Ranges seems to decrease toward the central Transverse Ranges, the Newport-Inglewood Fault and/or ~other near-shore faults are thought to accommodate most of discrepancy vector 3. 1 i Uncehues in the Modat \\ e The descripuon presented above is our best esumate, based on the data available, of the kinemaues of southern California. The data are not wou con-strained in several critical areas. Possible sources of error include failure to i consider straln resulting from kmaller structures possessing unknown rates, and inaccurate parameterization of the structures treated. Ideally, uncertalnues j could be accumulated along the route of integration at the same time that the l strain is calculated, so that at any point along the path an uncertainty could be given (relative to the beginning of the path). However, the nature of the uncer-taintles make them poorly suited to statistical treatment.,The slip rates are the "best estimates" of the workers from their'Seld areas, but the probabuity distri-buuon of the estimates are often asymmetric.and highly non Caussian. Inlieu of a formal treatment of the error, we discuss probable sources and magnitudes of l error and their quantitative effects on the block mouons and on the overall f kinemaue model There is considerable uncertainty in both the magnitude and direction of mouon of the Sierra block. Carter's sup rate of 11 mm/yr that we use in l l deducing the mouon of this block,is only absolutely constrained between 5 and 30 or more mm/yr (Carter.1982). However, his best esumate of 11 mm/yr is l based on several Hnes of geologic inference that we feel are quite good. Also, his rate is for the portion of the Carlock Tault'to the east of the Owens VaUey Tault. . whereas path 1 erosses the fault west of of this fault. The Owens Valley Tault j probably cannot contribute more than a few mm/yr even in its more methe

2 northern portion (Gillespie,1962). We feel that the inactivity of the southern l end of the Owens Vaney Fault allows us to estend Carter's estimate across the l [ fault and to the west. A related problem is that the Carlock Fault is quite i curved. We have chosen 555W because it is the trend of the fault in the region i whereit separates the Mojave from the Sierra block, and therefore should best I describe the block's local relative mouon. Note that chosing this portion of the Garlock Fault yields a slip vector orientation that is pointing as far counter-l clockwise as the trace of the Carlock Fault win allow. If translation of the Sierra 1 block is occurring in a more westerly dirscuen, the mouon of this block would be more in line with that chosen by Minster and Jordan (1984). The effect of nacreasing the slip rate on the Garlock Tault would be to increase the amount of convergence occurring offshore north of the Transverse Ranges and would be eenststent with a component of left-lateral shear occurring across the western 1tansverse Ranges. However,if the Sierra block is moving westward by rotating i i about a pole located approximately 200 km to the southeast, as suggested by the curvature of the Carlock Tault, the relauv,e velocity vector should be rotated i eeunterclockwise 20-25' by the time the lategration path rasches the San j Andreas Fault. The possibility of this rolaung movement is also suggested by t the sorthward leeresse in acuvity seroes the Owens Vaney Fault-(Gluespie, . 1982), and the presence of increasingly compressive faulting parauel to thsGar-lock Fault west of where our path crosses the Sierra block (Figure 3) (Davis and Lagos,1954). In our model the movement of the Sierra block is estimated by using infor-mation on the Garlock Fault. An alternauve approach, chosen by Minster and i f Jordan (1984), is to consider a path that.begins on stable North America and arrives at eentral California by crossing the Great Sasin. Though uncertainties l in the motions encountered along the path esist in both cases, we feel that there i ~ ~

_ _ _ _ ~ _ -. _ _ _ _ _ _ _ l 8 are fewer problems associated with the route we have chosen. This is due to the relatively large degree of uncerta'nty in tbs rate and crientation of extension across the Great' Basin. Other wor *cers have assumed that some of the motion on the Gprlock Tault is due to deformation or rotation of the Mojave block relauwe to North America. Ye believe that it is entirely due to the opening of the Great Basin. The fact that the Garlock Fault does not span the entire southern margin l of the Great Basin may be a problem. We feel, however, that an equally f signbicant problem is produced by appealing to a mobue Mojave block; that is the apparent absence of deformation on the eastern margin of this block. l Strain along path 2 in the region of the western Transverse Ranges is assumed to be purely convergent normal to the major faults and folds. and. 6 1 l ignores the leftlateral faults that combined are believed to secommodate less than E'mm/yr (Clark et al.,1963). The resulting velocity vector for an arbitrary point south of the zone of convergence is very close to the velocity vector for the Pacifle Plate (Minster and Jordan. 1978; 1984). Tids suggests that most of the California borderland west of the end of path I(Tigure 3)is indeed part of the Pseule Plate. Fath 3 has the least amount of uncertainty associated with its relative vele. sity vectors. The rates and' orie,ntations of all three ensbore strike slip faults crossed are fairly well constrained. For the San Andreas Fault we use Weldon and Sieh's (iln press) estimated rate of 24.5 mm/yr e 3.5 mm/yr and the orien-tation tangent to the circular are shown in Figure a that produces pure strike-slip motion along the San dndreas Tault. Sharp (1981) has determ!ned a rate of about 10 mm/yr on the Sah Jacinto Tault, and we have chosen an orientation that on average best describes that fault. Estimates of the slip rate across the l Deinors Tault vary from 1 mm/yr (Ziony and Yerkes.1954) to 7 mm/yr (Ken-medy.1977). New work on the southern Dsinore Tault (*4 mun/yr: Pinault and

Rockwou.1954) may help constrain the slip rate, but at the moment none of the estimates is as wen constrained as the other slip rates encountered along path

3. In our model we arbitraruy chose 2 mm/yr'to resect the consensus that the northern Dainore accommodates very little aup. If the lower estimate of 1 l

mm/yr is valid. It increases the discrepancy vector by a negligible amounL A ~ t l rate of 7 mm/yr reduces the discrepancy vector to about to mm/yr. a change of only 20%. No reasonable slip rate on the Etsinore Fault can change the con-clusion that a large fraction of the plate motion must be west of the Los Angeles ' block. Another possible source of error in our modells the uncertainty of the pole position about which the blocks are rotating. This soures of error must be sman because the path cwors less than 20% of the distance to the pole, and was ebosen so that no change in orientation occurs. The uncertalnty in the pole position cari contribute only a few mm/yr of arter to the total If the Salton Trough is opening with a component normal to the San Andreas Fault, as has been suggested by Biehler (pers. comm.1963), the pole may be farther away Nom the big bend region. This possible normal component in the Salton Trough, however. La not supported by Savage's (1983) strain data or by the arcuate At of the San Andreas shown in Figure 2. Another route similar to path 3 eeuld be taken across the San Andress Fault NW of the San Jacinto Tault, to the San Gabriel block, and then across the Sierra Madre Cucamonga Tault to the Pomona block. This is shown on Figure 3 as path 4. Crossing the San Andreas Tault picks up 35

  • 5 mm/yr (Weldon.

1954b) parallel to the San Andreas Tault, N85W. This gives a velocity for the San Gabriel block which is almilar to that found for the Salinia block with path 3. This is espected because there are no major acuve structures recognized between the two blocks. Rotating the Sierra block counterclockwise along the

? I . ns. f eurved Carlock Tault (as discussed above) will result in Salinia moving with a magnitude and direction even more similar to that of the San Gabriel block. Crossing the Cucamonga Fault to the Pomona block adds 3 mm/yr (Matill et al. f 1962: pers comm 1984) to the'relauve velocity vector'and rotates it clockwise !~ about 15'. The resultant Pomona block vector (corrected for rotation accumu-i Isted by traversing the block to path 3) is virtually identical to that calculated with path 3. Again, the consistency of the results determined with diSerent data sets along diferent paths tends to support the accuracy of the rates and the kinemaue model. Also, since the.Los Angeles block is moving parallel to the i Pomona b1xk. there remains about the same angular discordance between the ~ I j Ban Gabriel block and the Los Angeles block as exists between the San Gabriel and Pomona blocks. The change in orientation of the Sierra Madre-Cucamonga Fault zone to the west wul aSect the relauve amounts of convergence and lateral faulung along this boundary. Convergence on,the Sierra Madre-Cucamonga i Tault system is largely responsible for the current uplift of the centra! l Transverse Ranges. In our model this is due.to the slighuy diSerent direcuon of unouon of the Sen Gabriel block with respect to those to the south, and not to i ~ [ atmple convergence between the Pacios and North American Plates. l kaptieauens An important feature of our kinematic mode!is the predicuan of a zone of I very'acuve deformation oSshore. This is a consequence of the discrepancy vec-tors for paths 1. 3 and 4 and the eenvergence in the western Transverse Ranges all being nearly the same (vector diagrams. Figure 3). We propose that the discrepancy vectors for paths 1. 3 and 4 are accommodated on hT trending. predominately strike-slip faults near the coast, while convergence on,E W thrusts and folds in the western Transverse Ranges accommodate the same l 6 L

4 motion there. The style of activity varies because the elements diSer in orienta-l tion. In this " coastal system" the western Transverse Ranges form a left step between the more hT trending oSshore elements. Seismic studies support our l i i model of a switch from predominately strike-slip moUon on northwest trending faults'in the borderland to ersentially pure convergence in the western l Transverse Ranges (e.g., Corbett 1984). Unfortunately, the length of the seismic record is inadequate to asumate rates of deformaUon. The diminishing of convergent deformauon to the east and west of the western Transverse Ranges places the site of the oEshore faulting near the coastline both north and i south of the Transverse Ranges. This arrangement of,acuve features defines a t coastal system of acuve boundaries that separate the Pacifle Plate to the west kom a slice of relatively intact continental msterial to the sast. In southern California the coastal system la saly exposed onshore in the western Transverse Ranges. Measurements of the rate and direction of conver-gence across the western Transverse Ranges at various longitudes may provide s direct means of quantifying the location, rate, and style of motion on the hT 7 trending elements of the system that are not exposed onshore. We have caleu-lated that the end of path 2 is moving with the Paci8e Plate, but the distribution I ,of activity on the faults within the borderland between the end of path 2 and the las Angeles block cannot be determined unut the distribuuon of the convergent acuvity in the Transverse Ranges east of path g has been worked out in detall. or ~ until the slip rates of the underwater faults are determined. Another area where r constraint on the acuvity of the coastal system may esist is Baja California. l ' Allen et al. (1960) report quaternary deformaUon on the Ague Blanca Pault that indicates up to cenumeters/ year of activity joining the Gulf of California with the California borderland. Yeats and Hag (1951) also describe active features that run down the western length of Baja, suggesting that some of the Pse18e-e ~

v 17 4 North American plate motion never enters the Gulf of California. Another important consideration is the relation between the offshore activity and the value for the PaclSc-North American Plate relative mot {on. Ye accept the plate motion valus determined by Minster and Jordan (1978; 1984) and compara our integrated velocity to theirs. The motion on the NW trending i elements of the coastal system is determined by assigning the diSerence between the integrated strain.and the Pac 1Sc North American Plate motion on r these features. We feel justiSed in doing this because it is consistent with the slip estimates determined by the extension of paths 1. 3 and 4 to the end of path - 2, which is a purely traternal determination. Thlle the acquisition of the Pac 18e t i Plate velocity by the end of path 2 supperts the Pac 1Sc-North American Plate rates of Minster and Jordan (1975: 1954), we do rot intend for this to be taken as I strong evidence for the accuracy of their value. This is because we have accu-mulated'an unknown amount of uncertainty along path 2, and because their ~ rates are based on a 3 my average while ours are late Quaternary estimates. It is not yet known whether our model is valid for the tectonics prior to the late Qu'aternary. If the actual Pacioe-North American, Plate rate diSers somewhat from the value determined by Minster and Jordar. (1975: 1984), an internally consistent model could be, produced by only adjusting the model convergence rate in the western Transverse Ranges. The quality of the data from the western Transverse Ranges, however. probably does not aBow one to alter the model very much. We agree with the conclusion of Minster and Jordan (1984) that the conver-gence across the Paciac-North American plate boundary is due to the westward motion of central California'in response to the' opening of the Great Basin, and not 'due to the geometry of the San Andreas system. We feel that our rate and direction of motion for the Sierra block (11 mm/yr and 555Y) are better ..E.

a constrained than theirs. Further, if the Sierra block is rotating west, as sug-gested by the curvature of t'he Carlock Fault, the convergence in the Transverse Ranges near the junction of the Garlock Fault with the San Andreas Fault can be explained by the impingment of the SW corner of the Sierra block into the Salinia-San Gabriel block. We feel that this satisSes the geology (Davis and Lagoe,1954) better than appealing to the geometry of the San Andreas Garlock junction. Finally, our model suggests origins for the activity in the Transverse Ranges that diSer from previous accounts., These ranges have long been taken as evi-dence for southern California, as part of the Pac!Se Plate, to be coDiding into North America in the big bend region. However, our model(Figure 4) produces - uplift in the eastern Transverse Ranges with convergence across a step in the otherwise arcuate and strike-slip southern San Andreas Fault. The convergence across this.small step is 25 mm/yr oriented N50W. The central Transverse Ranges are being uplifted bi the Sierra Madre-Cucamonga Tault system. Con-vergence across this boundary is due to the different directions of motion of the San Gabriel block and tie blocks to the south. As shown in Figure 4. this geometry requires about 3 mm/yr of convergence across this sone. Activity in the western Transverse Ranges is due to a left step in the " coastal system", and i ~ is probably unrelated to the San Andreas Tault. Corbett (1954) notes that au well located earthquakes that occurred deeper than 20 km, and most that occurred deeper than 15 km (from 1971-1981), were either in the Banning Pass i area or in the western Transverse Ranges. This is thought to be due to the l existence of cold, brittle material at an unusually great depth as a result of the exceptional degree of convergence at these locations. This is supported by the anomalously high seismic velocity of the deep crust in the same locations (Hum-phreys.1954) -..-.--.J..-. -. =-:--..

33 t We feel that the major uncertainties in the tectonics of southern California are external to the region modeled. The opening of the Great Basin appears to control the motion of the Sierra block, which in turn controls the amoun} of con-vergence near and o5 of the central California coast. It is also felt that the simi-larity.in motion of the Salinia block with that of the San Gabriel block suggests that the extension in the Great Basin (which controls the motion of the Salinia block) is related to the rotation of southern California (which controls the motion of the San Gabriel block). Furthermore, the degree to which the Mojave block is part of North America direcuy aSects the amount of activity required oSshore to satisfy the plate bo6ndary conditions. The value chosen for the Instantaneous plate velocity afects the estimates of o# shore activity in a com-pletely analogous way. In spite of these external uncertainues,it is the internal consistency of the model, which includes the coastal system through the activity documented in the western Transverse Ranges, that suggests to us that the. kinemaues of southern California ar's now reasonEbly well understood. The ain- ~ I gle Us across the western Transverse Ranges to the borderland leaves the coa-stal system as the least certain past of the mods!, but the agreement of the velocity at the end of path 2 (which crosses the western hansverse Ranges) with .i the externally derived value for the velocity of the Paciac Plate (Minster and Jor-dan 1978; 1964) lends additional support for the nature of the coastal acuvity. The magnitude of the otshore acurity implies that the region between the San Andreas Fault and the coastal system may be thought of as a mini plate that is-neither part of the North Arnerican Plate or the Pacioc Plate. O e .g e ,a.--,--+ n,.. +n..

go. 4 e Acknowledgements . This paper is based on the 8 eld work and thoughts of innurnerable people who have worked in southern California. We would like to acknowledge all of those workers referenced in the bibliography and to especially thank those who t have freely shared their unpublished data and ideas upon which our modelis based. We are particularly grateful to 14on Silver Clarence Allen. Brad Hager, Kerry Sieb Kris Meis11ng and Steve Wesnousky; who lent critical discussion and/or detailed reviews of the Srst draft of this manuscripL We thank Jan Mayne for assistance in the pre'paration of the Sgures. e G e e e 4 9 4 E e

~ ~ - - - e .* References Cited Allen, C,R., Silver, L.T., ;and Stehli, F.C.,1960, Agua Blanca fault-a major transverse structure of northern Baja California, hexico: Geological ' Society of America Bulletin, v. 71, p. 457-482. Anderson, D.L.,1971. The San Andress faults Scientific American, v. 225

  1. 5, p. 52-68.

Anderson, J.C., 1979. Estimating the seismicity from geological structure for seismic-risk studies: Bulletin of the Seismological Society of America, v. 69, p.135-158. i Atwater. T., 1970, Implicatio'ns of plate tectonics for the Canosoic tectonic evolution of western North America: Geological Society of America Bulletin,

v. 81, p. 3513-3536.

Barrows A.C., 1979. Geology and fault activity of the Yalyerno segment of the t San Andreas fault none,Ims Angeles County, California: California Division of Mines and Geology, Open-File Report 79-1 1A, 49 p. Bird, P. and Rosenstock, LU.,1984. Kinematics of present crust and mantle flow in southern California: Geological Society of America Bulletin,v. 95,

p. 946-957.

Calderone, C. and Butler, R.F., 1984 Faleomagnetism of Miocene volcanic rocks'from southwestern Arizona: 1hetonic implications: Geology,v. 12,

p. 627-630.

Carter, B.A., 1980, quaternary displacement on the Garlock fault, California, g Fife, D.L. and Brown A.L. g., Geology and mineral unalth of 'the California desert, Dibbles Volume: South Cosst Geological Society, Santa Ana, California, p. 457 4 65. Carter, B.A.,1982. Neogene displacement on the Garlock fault, California (abstract): American Geophysical Union Transactions. EOS, v. 63, p.1124. l Clark, N.M., Enras, K.K., Lienkaesper, J.J., Esrwood, D.S., Lajoie. E.L. -e,- -._-,,_..rm_,,_ ~.._,m-,,--.,4,_ _._,mywe,#ww-,m,m.,w_,wwm,,-p,v,,

i- \\ \\ i i-1 Matti, J.C., Perkins, J. A., Rymer, M.J., Sarna-Woj cicki, A.M., Sharp, 1.V., Sims, J.D., Tinsley, J.C. III, and Ziony, J.I., 1983, Preliminary J i slip rate table and asp of late Quaternary faults of California: preprint i of.U.S. Geological Survey Open File Report. Corbett, E.J.,1984, Seismicity and crustal structure studies of southern f California: Thetonic implications from improved earthquake locations: PhD Dissertation, Caltech, 231 p. Crouch, J.K. Bachman, 8.3., and Shay, J.T.,1984, Post Miocene compressional tectonics along the central California margin, g Crouch, J.K. and Bachman. 5.3.,eg.,1hetonicsandsedimentationalongtheCaliforniamargin: i Pacific Section S.LP.M., v. 38, p. 37-54. Crowell, J.C.,1981, An outline of the tectonic history of southeastern Cali-fornia, g. Ernet W.G., g., The geotectonic development of California, Bubey Yolume #1: Frantice-Ball, New Jersey, p. 583-600. ~ ' l Davis, T. and Lagoe, M., 1984, Cenosoic structural development of the sorth-t I central Transverse Banges and southern margin of the San Joaquin Valley: Abstracts with Programs, 97th Annual Meeting, Geological Society of ~ America, v.16, p. 484. Dokka. LE.,1983, Displacements on late Canosoic strike slip faults of the central Mojave desert California: Geology, v. 11, p. 305-308. l Eh113 F.L.,1981, Origin and tectonic history of the basement terrane of 1 the San Gabriel Mountains, central Transverse Banges, g Ernst, U.G., g., the geotectonic development of California, kbey Volume #1: Frontice-Ball, New Jersey, p. 253-283. Ehlig, F.L., Ehlert, E.i., and Crowe, 3.M.,1975, offset of the upper ( Miocene Caliente and Mint Canyon forestions along the San Gabriel and San Andress faults, g Crowell, J.C., o_d,.. San 'Andreas fault in southern d 7"-ewWe.emew-,-,.e.w-m,

i.. 23 - California: A guide to. San Andreas fault from Mexico to Carrizo plains California Division of Mines and Geology, Special Report 118, p. 83-92. Foster, J.B.,1980. Late Cenosoic tectonic evolution of Cajon Valley: PhD 1 Dissartation, University of California, Riverside, 242 p. Garfunkel. E., 1974 Model for the late Cenosoic tectonic history of the t 4 Mojave desert, California: Geological Society of America Bulletin, v. 85

p. 1931-1944.

Gillespie, A.R., 1982, Quaternary glaciation and tectonism in the southeastern Sierra Nevada, Inyo County, California: PhD Dissertation, Caltech, 695 p. i Elli, D.F., 1982. Contemporary block tectonics: California and Nevada: Journal of Geophysical Research, v. 87, p. 5433-5650. Ramphreys, L 1984, A tomographic inversion for seismic structure beneath southern California: Besults and implications: PhD Dissertation, Caltech. Ramphreys L and Bager, 3.E.,1984, Small'-scale convection beneath the Trans-verse Ranges, southern California (abstract): American Geophysical Union Transactions. EOS, v. 65, #16. F.195. Eennedy. EP.,1977. Recency and character.of faulting along the Elsinore l fault sone in southern Riverside County, California: California Division of Mines and Geology, Special Esport 131,12 s. Rosloff, D.D., k978 Numerical models of crustal deformation: PhD Disserts-L tion, Caltech. - Luyendyk, 3.F., Esserling, EJ., and 1hrres E.,1980 Geometric model for Neogene crostal rotations in southern California: Geological Society of America sulletin, v. 91, p. 211-217. Matti, J.C. and Morton, D.L.1975, Geologic history of the San Timoteo badlands, s'outhern California: Abstracts with Programs, Cordilleran Section, Geological Society of America, v. 7, #3, p. 344. w- -~rw -m-+. w m e r- -+-on,- .,,,-w..,,,w,,, .9- --wm,.,_a----,,mme--,e,e _~s-o,ww,,,-m --m., mm,m mwm,,--mw_nwwww--~wm,,w

_m e l-

i.

Matti, J.C., Tinsley, J.C., Morton, D.M., and McFadden, L.D.,1982, Bolocene ,fnulting history as recorded by alluvial stratigraphy within the Cuca-songs fault ' sone - a preliminary view, g Tinsley, J.C., McFadden, L.D., and Matti, J.C., eds., Late Quaternary pedogenesis and alluvial stratigraphy within the Cucamonga fault zone: Geological Society of America, Cordilleran Section, Field Trip Guide #12, p. 21-44. Matti, J.C., Morton, D.M., and Cox, 3.F., 1984, Geologic framework of the south-central Transverse Ranges, southern California: Distribution and nomenclature of faults in the, San Andreas fault mone and associated fault systems: preprint. Morton, D.M. and Matti, J.C.,1979 Bridence for a vanished post-siddle f Miocene pre-late Pleistocene alluvial-fan complaz in the northern Ferris l i block, southern California: Abstracts with Programs, Cordilleran Section, Geological Society of America, v. 11, p. 118. Journal of Minster, J.B. and Jordan, T.B., 1978. Present-day piste notions: Geophysical Basearch, v. 83, p. 5331,5354. Minster, J.B. and Jordan, T.B., 1984. Vector constraints on Quaternary defor-nation of the western United States east and west of the San Andress fault, g Crouc'a, J.E. and Bachman, S.B., g., llectonics and sedimentation along the California margin: Facific Section 5.LP.M., v. 38, preprint. Finsult, C.T. and Bockwell, T.E.,1984. Estes and sense of Bolocene faulting on the southern Elsinore Fault: Further constraints on the distribution of dextral shear between the Pacific and North American plates: Abstracts with Programs, 97th Annual Meeting, Geological Society of America, v.16, p. 624. Powell, R.E.,1981 Geology of the crys,talline basement complex, eastern Trans-verse.Banges, southern California: Constraints on regional tectonic inter-pretation: PhD Dissertation Caltech, A41 p. ..-..=.==.=--.-:- =.

6 -- -~ ' - ~ t Rockwell, T.K.,1983. Soil chronology, geology, and neotectonics of the north central Ventura basin, California: PhD Dissertation, University of Cali- ^ fornia, Santa Barbara, 424 p. Savage, J.C.,1983, Strain accumuistion in western United States: Annual Review of Flanetary Sciences, v.11, p.11-43. Sharp, R.V., 1981 Variable rates of late Quaternary strike slip on the San Jacinto fault none Southern California: Journal of Geophysical Sesearch,

v. 86, p. 1754-1762.

Sieb, K.L and Jahns L,1984, Bolocene activity of the San Andress fault at Wallace Creek, California: Geological Society of America Sulletin,

v. 95, p. 883-896.

Silver, L.T.,1982. Evidence and a model for west-directed early to mid-Cenosoic basement overthrusting in southern California: Abstracts with Programs, Cordilleran Section, Geological Society of America, v.14 ~ ~

p. 617.

Weber, G.L and lajoie, E.R.,1977, Late Pleistocene and blocene tectonics of the San Gregorio fault none between Moss Seach and Point Ano Nuevo, ~ San Mateo County, California: Abstracts with Programs, Cord tiaran ~ Section, Geological Society of America, v. 9, p. 524. Ueldon, LJ.,1984a, quaternary deformation due to the junction of the San Andreas and San Jacinto Faults. Southern California, Abstracts with Pro-grams, 97th Annual Meeting, Geological Society of America, v.16, p. 689. Weldon, LJ.,1984b, Implications of the age and distribution of the late Cenosoic stratigraphy in Cajon Pass Southern California, g Bester, R4L. and Enllinger,*D.L. g., San Andreas Fault - Cajon Fass to Wrightwood, Pacific Section A.A.F.C., Guidebook 55, p. 5-16. Weldon, LJ. and Sieh, K.L. Eslocene rate of slip and tentative recurrence =

. 1 - l interval for large earthquakas on the San Andreas Fault in Cajon l Pass, Southern California: Geological Society of America Bulletin, in press. Weldon, R.J., Winston, D.S., Kirscheink, J.L. and Burbank, D.W.,1984, hgnetic stratigraphy of the Crowder Formation, Cajon Pass, Southern t f California, Abstracts with Programs: 97th Annual Meeting, Geological Society of America, v.16, p. 689. l Yeats, 1.5., 1983, Large s' gale quaternary detacaments in Ventura Basin, southern California, Journal of Geophysical Research, v. 88, p. 569-583. Yeats, R.S. and Eng, 3.U.,1981 Deep ses drilling off the Californias; Implications of leg 63, g lag 63 of the cruisas of the drilling vessel Glomar Challenger, Icag Beach, California to Masatlan, Mexico, October-l November,19781 Initial Esports of the Deep Sea Drilling Project, v. 63,

p. 949-961.

Ziony, J.I. and Yerkes, R.F.,1984, Fault slip-rate estimation for the las Angeles region: Challenges and opportunit'tes (abstract): Earthquake Notes. Eastern Section, Seismological Society of America, v. '55, #1, p. 8. ~* [ l t e e -e,pev- , + -. +m.w-,9

,1 ~ 17 - FICURE CAPTIONS 1 1 t Figure 'l - The principle faults of southern California and the subdivisions 1 } of the Transverse Ranges used in this paper. h oe faults are assumed to bound erssentially rigid blocks that are modeled as moving in directions con-j sistent with the faults that bound them. The broad deformation associated l with the western Transverse Ranges is modeled as a simple boundary, parallel i to the zone. t Figure 2 - The major blocks in southern California and the data used to cal-i culate their velocities relati're to North America. h arcs have been fit to the trend of the San Andreas fault to determine the direction of motion i of southern California west of the fault,. Only the area between the northern 1 big band, the Salton trough and the Pacific coast is rotating along the arcs. f The principle strain rates from 3 trila,teration networks in southern Califor-aia and the average velocity field across the Salton network (Savage 1983) are included to demonstrate the consistency of this data with the curvature L. of the fault. 1he slip rates (mm/yr) used in the model are located where the integration paths (Fig. 3) cross the faults. The letters associated i with the rates are the references from which the rates were chosen: a) Sieh l l and Jahns, 1984; b) Carter, 1980; 1984; c) Weldon, 1984; d) Weldon and Sieb, l 1984; e) Sharp, 1981; f) Matti et al 1982; g) see tent; b) Yeats, 1983. Figure 3 - integration paths and slip vectors for the major blocks in southern t California. The solid arrows are the velocity vectors relative to North America for points along the paths and the ve: tor diagrams show the data used to construct these vectors. Because the' southern Californ% blocks are rotating about a relatively close pole, the velocity vectors vary by a small but significant amount across the blocks (see tent). The corrections .~e. ._wm,,. -,_m,.w..,,,.w y-..n, _,,,%,wm..,,mmw,,.wm,,,.* m ,,eg,ywy,.

i e

  • \\

- gg - are included in the vector' diagrams as vectors with points instead of heads. The " hollow" arrows at the end of Faths 1, 3 and 4 (on both the map and the vector diagrams) are the discrepancy vectors, the motion necessary to bring the path up to the relative plate motion between the Pacific and North American plates (Facific-North American plate motion form Minster and Jordan, 1984). Only Fath 2 yields the total plate motion, i indicating that more than 1/3 of the plate motion is accommodated by structures close to or off of the California coastline (see text). Fikvre 4 - Schenstic representation of the active deformation in the J Transverse Ranges. The eastern Transverse Ranges are being uplifted by convergence across a step in the San Andreas fault, indicating a rate of 4 convergence of 25 mm/yr oriented N50W. The western Transverse Ranges are being compressed by a similar left step in the hypothesized coasta1 system, at a rate of 23 am/yr oriented about N5W. The central stans-verse ranges are only experiencing minor uplift, due to the difference in direction of motion of the San Gabriel block and southern C lifornia. '2he direction and magnitude of this compression is difficult to determine from the model alona. If the rates of motion are the same and all of the convergence is d'un to the difference in direction, the model suggests a rate of 3 mm/yr oriented N25E. Ibwever, small' changes in the relative magnitudes of the. motions change the orientation of the convergence by large amounts. 1here is about 11 mm/yr of convergence perpendicular to the San Andress fault and the Pacific margin north of the Carlock fault due to the opening of the Crest Basin. If the Sierra block is rotating west, as the curvature of the Garlock implies, there should be 3-5 mm/yr 4 of NS convergence where the SW corner of the Sierra block impinges on the Salinia-San Gabriel block. n.. .~ t

pw,,

  • t.

)i g g s k l \\- m I \\ K \\ \\ )! \\ \\ / l ['. I %N I ) / / 1 m E ~l I f* A g / t t N f q _ _ o.n.... [ ki s,hi, y \\ ~. ,o c-

  • h, 4

L q \\. +%,*s % k 1-t v\\ t i

1

{ L 11

  • I 1

s N fi .i,6 { g = I L, ..... J / + ~..,_ ~.. j__ ~ L" l ? a / s ~ / **x / ~ syd l

.s t i l t' '+. 4/ t 4 /# f / \\ ~ g \\ / Sierra Salinia \\ Great Basin i \\. ,/ 5 - %.11 4 'b s d,

  • Mojava g

\\_ ga s k s, \\; 7 .g ,I Ik i Pacific 1,.g(Ah e pg 3 ,\\ t i . N. t l........y

  • q

\\ ..,1jl}1 ( l{h t t /

  • s t

4 l -8 I., [ .'...,i 90 mwyr) ,,e,e,e, trem sewege (194., F4 f) 4 e e .orecone erae votes ,8 4 s 4 n g ${fh 1 l

l \\ ++ p i \\ 3 I ) 4

  • +

E / /! ('. Path 1 r l '*'hJ.~.{ f. \\, mj/ i[T 7 I i .y p -h\\ \\, Path 1 and 2 i, f i ~ yv j %) N s. P h2 f+s

  1. Gi-I f,pyi, '

dse,rg,4 j / - "h .h 9{ / 5 g, r s-.. r w I \\; -/ >f r E ss { h\\ $; )/,,,, {}+, b I i s-( ,s j Path 3 I \\ ~ J L '++1 \\ k i er g-cr j ,.. ~ ~ ~ g E + + f I s sar g l 4 + g-f L., Path 4 a l . -- j } j 3 k q} 's so mw,, frelseve to Norm Amortal g 0 4dometers sic

8..

u=.=.

.t Mo g 3 o a CONVERGENCE ACROSS a e' THE TRANSVERSE RANGES Central California: 11 mm/yr S55W 4 North Central Transverse Ranges: 3-5 mm/yr NS / Western Transverse Ranges: 23mm/yr - N5W

  • g S.

Central Transverse Ranges: 3 mm/yr N25E + CD Eastern Transverse l o Ranges: 25 mm/yr e N50W 9 m ~ ~ 0 kilometers 100 5 Southern NORTH PACIFIC PLATE California AMERICA g - ~+

m.

[ b -_..w..w._,,--w,-w--,w.-m.,,w..,c,,-,,m#,,,,, - -... e w s r e ve' - - -}}

Retrieved from "https://kanterella.com/w/index.php?title=ML20105A732&oldid=4302664"