Journal of Geophysical Research: Solid Earth, P.E2020jb020017

Home , Propagating rift

Marine vertical gravity gradients reveal the global distribution and tectonic significance of “seesaw” ridge propagation Hugh Harper 1, Brook Tozer 1, David T. Sandwell 1 and Richard N. Hey 2

1 Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, CA 2Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, HI Corresponding author: Hugh Harper ( [email protected] )

Key Points: • The process of “seesaw” ridge propagation is ubiquitous on seafloor that forms at half spreading rates between 10–40 mm yr -1 • Globally, the total length of seesaw propagators is ~ 1/3 that of fracture zones • Driving mechanisms previously proposed to explain unidirectional ridge propagation fail

Article account for the behavior of seesaw propagators

Accepted

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This article is protected by copyright. All rights reserved. (i.e., intermediate- to slow-spreading), the ridges intermediate-to slow-spreading), (i.e., the tectonics occurs over the half rate tectonics occurs spreadingover the range that 1991) haveMalinverno, Morgan, proposed 1990; autho al., 1995). (e.g., developmentSeveralHey et andfaults,of width transform the ridge-to-ridgep axi valley orof foran presence axial example, the Sandwell, Small 1994; 1993; &&Phipps-Morgan Chen, andMacdonald al.,Small 1987; Macdonald,et1982; the thermal an structure andspreading rate, hence, thestylesegment morphology ridges and of their of A thorough review of ridge segmentation can be foun can Areviewbe ridge thoroughsegmentation of in the con and(Langmuir et disruptions al., 1986), deviation including in rial., (Macdonald1991), et centerset overlappingspreading al., (Macdonald 19 ridg including propagating faults, stable transform quick wasdiscontinuities wide andridge variety of an ridges surveyingmagnetic (Schouten the began of features became These forms ridge discontinuity. of Macdonaldspreadingfast al., 1988) ridges (e.g. et motionof that the spreadingrecordplates. Alo the timeand probecauseare stable they in space, they of exhibitingridge of discontinuity, lateral large T poorlysegment understood. remain discontinuities yetregarmany features of details the ocean floor, 1 Introduction Introduction 1 unidirectional invoked ridge propagation to explain becannot uncorrelated andspace and appear largely (3youngTh(4)km) formed thin lithosphere. onand modell Isostatic(3)“non-rigid” for SSP behavior. a wher which likelythreshold, rheological reflects (0–2.5 offsetSSPs age(2) across The lithospheric Abstract Abstract spreading rates between 10–40 mm yr10–40 mm spreading betweenrates a (1) documentedfind globallythat: SSPs and these “seesawrefer wethe seafloor to as which propagato featurescommonlyreverse propagatingridges,these bou some atsegment ofoccurrence ridgepropagation that areridg seafloor off-axis oblique to features gradgravity verticalanalyze satellite-derived new bo operating atyetprocesses segment tectonic some

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article As these features continued to be discovered, it so to be continued discovered, it As these features Segmentation of the global mid ocean ridge (MOR) sy mid(MOR) global Segmentation ocean ridgeof the The segmentation of mid-ocean ridges is ridgesa defining Theis mid-ocean segmentation of -1 and their total length abouttotal their1/3 and is fsets (> 30 km) of the ridges (Wilson,km) 30 ridges 1965); (> of fsets the es and transform faults and thus reflectthus faults transformand the and es are characterized by axial valleys transformand byare axial characterized ding the tectonic processes that that occurat processes the the tectonic ding resence of ridge propagation or microplate resence propagation of ridge al andstrike high, in the spacing along changes dge axis linearity, changes in in ridge linearity,dge petrology changes axis ient (VGG) data, which reveal anreveal of (VGG) which abundance ient data, of ~ 25-40 mm yrmmof ~ 25-40 there also exist stablesmaller-scale,there andalso exist less eby only young allows weakand lithosphere eby only es (also knownrifts, (alsoal.,Hey 1986),as et es d strength of the oceanic plates (e.g., plates strengthd the oceanic of tinuity of the magma lens et (Kent magmatinuityal., 1990). of lens the etand Sempere al., 1990) slow (e.g.ng both duce the pronounced off-axis fracture duce pronouncedzones off-axis the ing of well-surveyed SSPs confirms ing they SSPs of that well-surveyed Ma) is less than transform faults (2–10 Ma),faults transform(2–10 than Ma) is less rs (Small and Sandwell, 1994; Chen and Chen1994; rs Sandwell, (Small and ly recognized (Macdonald et al., (Macdonald 1991), ly recognized and thus require a different driving force. aforce.require different thusdriving and ation are ationtothe seafloor intrinsically related re ubiquitous on seafloor that that formed seafloor at reon half ubiquitous 88),smaller-scale anddiscontinuities even apparent once detailed bathymetricand apparent once detailed rs” we (SSPs). the VGG, have Using explained by previous regional-scale models regional-scalebyexplained previous undaries remain poorly understood. Here, we understood. remainundaries poorly e directional changes oftimeSSPs e in both directional changes direction leaving W-shaped signatures direction leavingin ransform faults are the most obvious formmost obvious areransform the faults d White,theprevalence 1980),which, afterd d al.,in Carbotte d (2015). et ndaries.manyHowever,unlike Sandwell, 1989; Chen & Morgan,Chen Sandwell,& 1989; 1990; a major transition in the inthe style a MOR major transition of Dunn, 2015). Such Dunn, include,variationsSuch 2015). on became apparent that the the overall on that became apparent characteristic of seafloor spreading,ofcharacteristicseafloor stem is one of the most prominent onemost stem ofis the -1 . At rates lower this than rates At .

that of zones.fracturethat usually occurs in discrete steps (i.e., the (i.e., discont steps usually occurs in discrete with the areconsistent They the find that NTDs all gravity documen anomalies, and to satellite-derived multi Mid-Atlanticand N24 27.5uses between Ridge ridge framework.NTDsarefer propagating to within whichthey at thediscontinuities and“fossil” SSPs th (SSPs)to describe“seesaw the term propagators” andtheVGG appear interme slow in at ubiquitous so Wilson,weBecause—aset 1990). al., 1983; Johnson e “dueling(Macdonald dubbedhave been propagators” directionalso o havebeen reversals in propagation Figure reverses propagationeventuallyand 1 (e.g. theraterates that higher of is propagat spreading Themaintip. of b the propagating ridge difference blocks and outer pseudofaults) transferredcrustal NTDsshow of Theyevolution found structures NTDs. Zheng A Sempere,study recent by Cochran 1997). and at high resolutionmapped axis have offusing been al., HeyHey1978;McKe 1986; Rea,etet al., 1980; al., 1991) " and as (Grindlay "discordant zones" et Figure.(e.g. ridge1c). flanksW-patterns inthe behave documentedoffset. These of type propagating t sheared betweenandin zone the outer pseudofault thethanout more complex sheared is zoneand wider equal that is to the off the figure)a width having tothe right pla transferredthe plateleft wasand “inner” rift, failed andbounded by pseudofault the zone. that fracture of that aresembles expression smallage pseudofault a Ma) 1 represents (~ offset a pseudofault parallelthebehind ridgeleaving to the (PR).in offset small Theretransform-like is a Figureanomalies.magnetic pairs 1a shows in marine obs characterizedwere Heywho (1977) by originally 2011; al.,Dannowski1996; Hey,et Korenaga1994; & spreadingof centersultraslow exception Hey (e.g., both ridges and troughs with smaller amplitudes.ridgeswith both troughs and axis widelyalong transformmore spaced faults are (i.e.,at Conversely, higher fast-s rates spreading prominent have faultszonestroughs th fractureand

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article In our more global analysis, we follow the recent t follow wethe recent global In more analysis, our ther intermediate-spreadingandridges,Along slow- The process of ridge propagation has beenhas of ridgeThedocumente propagation process inuous propagation model of Hey et al., 1986). Heyet of al., propagation 1986). model inuous te. This transfer produces a sheared zone (S1 in transferin sheared This (S1zone a produces te. preading) the ridge axis has high, axis an axial the the ridge preading) These features have previously been previouslyreferred been to features have These set of the transform. The morphologyTheof of the transform.the set ion is highly variable and the the direction and of is highly variableion spreading ridge, which, over time, “migrates”time, spreadingwhich, over ridge, On the right is a broader shearedazone,On broaderthe right is on the left (P1 in the figure). This “outer”figure). the (P1leftonthe This in between ridge flanks by discontinuous jumps betweendiscontinuous flanks by ridge non-transform discontinuities" (NTDs) (e.g., discontinuities" non-transform that consists ofcrust consists that onoriginally that formed arise as NTDs or “active” SSPs. “active”or SSPs. as NTDs arise in thetopographicseafloora in has and propagating rift model wheremodel propagating rift propagation andspreading ridges bservedfaster PRs at at ShortFigure 2019).et Zheng al., of 1 at found andetween the NTDs propagators et al., 1986; Phipps-Morgan &Sandwell, al., Phipps-Morgan1986; et at are typically spaced ~ 50–80~are kmat spacedapart. typically multibeam sonar (e.g.Grindlayetmultibeam al., sonar 1991; (~100–1000 km) and the zonesfracture (~100–1000have the km)and t the traces and age offsets of and the t NTDs. the agetracesoffsets heseafloormorphology. nzie, 1986; Macdonald et al.,few 1988) etbutMacdonald 1986; nzie, ese NTDs. Wefeaturesoff-axisas ese referNTDs. to a schematic for a typical propagating ridge a propagatingschematica for typical diate spreading regimes, we adopted have regimes, spreading diate er pseudofault and thus one pseudofault thuser and can distinguish Their detailed analysis of a of region the analysis Their detailed erved the off-axis V-shaped pseudofault V-shapedpseudofault erved theoff-axis similarly to PRs but produce PRs but distinctive similarly to document in this paper—such features paper—such this documentnow in beam bathymetry, marine beambathymetry,magnetic Zheng Ridge al., 2019). et propagators et al. (2019) examined the long-termetexamined (2019) al. t al., 1988; Macdonald et al., 1992; al., 1992; al.,etMacdonald 1988; t typical of rift propagation (inner and propagation (inner rift typical of erminology of Zheng et al., (2019) and al., (2019) erminologyet of Zheng e exists a unique but a poorly unique but exists e d at all spreading rates with with rates the spreading all at d improvements (e.g., Figure 2) to analyze SSPs globa FigureSSPs improvementstoanalyze 2) (e.g., al, et (Sandwell 20 (2011)usedetMatthews by al., of aboutk resolution grida16 gravity spatial has gravity free-air V andglobal resolution and of the altimetryqualityand increashas satellite data of mapsth identifygradientverticalgravity(VGG) to o al., who, (2011), in lieu etMatthews and (2002), of & Sa Phipps-Morgan regional/global compilations a different style ofa rift propagation. different style et a al., of the (2019) conclusions the Zhengstudy i analysisusually morenot globalmodel. does Our allhas their the fundament NTDs that model that of that late can 20-30 accommodate kmrift valley wide from penetrat seawater weakenedby serpentinization is relativelycrustan thinrestricted thewhere to abutspreading rift tips First,becausetheslower themodel as spreading develope with compared crust betweenThey the differencesdetailed several noted propagation for unidirectional propagators the propagationforfor unidirectional neas aused propagationdirection reversals can be w crust in agreement compensated locally thinned by t (MH370). This shows 370 Flight AirlinesMalaysia comultibeam bathymetric data using high-resolution transform faults. transform faults. ofacrossage the r determineand range offsets the Indian Ocean basins. OceanIndian basins. SSPs total 370 features apair pairs), (73 for(185 V modifiedhave we new many(2011), to fit of which We ( SSPs.features previously 224 use unidentified categorizones,asdiscordant classified we broadly Mat identified byrefinedof features digitizations

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article (1) We VGG maps (1) thedigitiz newand to identify use newinourglobalfeatures cat Some included of the (3) Wemorphologythe(3) detailed and investigate isos (4) Wearesymmetri SSPs (4)tracesof that demonstrate (5) Finally, we test the validity of models previouFinally,test (5)of the validity we (2) We quantify the range of spreading rates where We where ratesof spreading (2) the range quantify d the shallower than normal mantle is likely to mantleto be is likely shallower normal than the d ed substantially, thus improving the accuracyimprovingsubstantially, thus ed relatively cold lithosphere, propagation is propagationis coldrelatively lithosphere, s), most of which are located in theAtlantic are most and in of whichlocated s), m compared to a resolution gridkmof m 22 resolution in the to acompared thews et al., (2011). Though many Though etwere al., (2011). thews GG grids (Sandwell et al., 2019). The newest Thegrids al., GG 2019). newest et (Sandwell nd assert the off-axis traces of all NTDs reflect tracesNTDsof allnd theassertoff-axis reflect idge discontinuities as with idgecompared discontinuities case of seesaw propagation. propagation. case of seesaw f bathymetry data, used satellite-derivedbathymetry fdata, used ze them as NTD/SSPs, and we alsoadded and ze as them NTD/SSPs, w data type for detailed plate w reconstructions. detailed data for plate type 19). In this study, we take advantage of these In of 19).advantage these study,this take we ese features. Since these studies, the amount amount Since the ese studies, features. these nclude such high-resolution data, we so ncludehigh-resolution adopt such al propagatingrift features of the standard propagation mechanism of NTDs in in slowerpropagationmechanism of NTDs 112 pairs) identified by Matthews etMatthews pairs)al. 112 identified by lly. Our study comprises five components: fivestudylly.comprises Our components: ral jumps in the rift axis. ralThey conclude jumps in the rift llected as part of the search for the missing the for llected of as the part search ion. Second, the slower spreading rifthasspreading a Second,ion. slower the ith Zheng al., (2019). ith et hese off-axis featuresare hese off-axis isostatically d at intermediate and fastridges. spreading atdand intermediate ndwell, (1994), Briais and Rabinowicz Briais (1994), ndwell, GG maps. Wean 146 maps. identifyadditional GG sly proposed to explain the directionexplain of to proposed sly alogue were included in the the previous alogue in were included we observe this style of propagationstyle we of this observe tatic compensation of off-axis SSPsoff-axis of compensationtatic c about the ridge such that cabout the that ridge such e SSP pairs. Many of theseeof SSPare Many pairs. Figure1. al., 1986). (b-c) The direction ofpropagation (b-c) al., The1986).reve direction ofrotated blocks (i.e., sheared azone series has The ridge. ordinaryouter pseu eastward propagating “outer” the (P1 l Ma pseudofault of VGGat shows 17 andridgesareso gradient (VGG)rotated up-down is

Evolution of a seesaw propagator in the Southeast seesaw of ain the propagatorEvolution the discontinuous propagation model Hey propagation the discontinuous et of rses resulting in a W-shaped scarVGGrses in a in the resulting dofault has a straight trough ahasdofault the straight while transforms are left-right. (a) Reconstruction are (a) transforms left-right. eft) and sheared zone (S1 an right) shearedandof zone eft) Indian Ocean. The vertical gravityThe vertical Ocean. Indian

(e.g., al.,Sandwell 20 papers et found in previous ofthesedata and regardingDetails acquisition the related to the gravitational potential relatedgravitational potential to the vertical gravity gradient is gradientverticalgravityis geoid height curvatureof practice,the ocean sur VGG is the the to mappingare 1997),relatively that suited better highlight variations wavelengthused shorter to the 2. Data 2. Data in the or morereversals seesaw one has propagator in anordinarypropagationresulting zone fracture a by increases offset at Ma. transform(d-e) 13 The acceleration of gravity. The potential satisfies L The satisfies gravity.potential accelerationof their similarities with ordinarytheir with propagating ridges similarities that these newhave claritydataextra provided by (einolderVGGmaps evident SSPs propagators.were h abyssal includingsmall-scale tectonic structures resultedle anoisehowever, lower significantly in Ka-b thefirstnon-repeat CryoSat-2, and Jason-1/2, a wealth of dataowing of obta to the new inclusion Improvements in the waves)accur is also amplified. wavelengthderivative,short of the back signal the

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article The VGG is gThe VGGis To identify and digitize SSPs globally, we globally, primarilTo digitizewe SSPsand identify gradient gravity Marine2.1 vertical , which is equal to the height of the ocean to the heightsurface ofwhichis equal the , z ()/ = () − = by Brun's formula by formula Brun's , so, , where, = aplace’s equation aplace’s is the horizontal position vector. The VGG isvector. the horizontal is Theposition fine-scale seafloor tectonic structures. Infine-scale structures.seafloor tectonic 19). 19). . . vel (e.g. Figurehelped vel (e.g.the reveal has 2). This derivation of the gridded globalgriddedmap ofderivationthecan be ills, smallseesawseamounts, now ills, and with Asymmetricalends.at the with distal V's revealed their symmetry across ridges andtheir revealed the symmetry ground noise (predominantlyfrom groundocean noise in the gravitytheWesselLyons, (e.g., in field and face as measured by satellite altimetry. Themeasured faceassatellite by symmetric spreading which stops ridgestops which symmetric spreading ined over the past eight years from altimetersyearsfrom eight overined thepast and altimeter, and SARAL/AltiKa—have, direction of propagation. direction of propagation. acy and spatial resolution oftheVGG— resolution acy spatial and .g. Matthews et al., 2011), but it is theMatthews is al., 2011),it but .g. et + / = y used the VGG grid version 29 (v29). 29 gridy VGGversion used the . Unfortunately, by takingUnfortunately, .bythis above the reference ellipsoid, is is thereference ellipsoid, above where + + is theaverage is 0 = theand

the North MAR. the North MAR. of (many discontinuities behavior of non-transform a et al., Dannowski more(2018) recently Ridge; and Sempéré etGoff and andMAR; a north(1997) Cochran along RidgeSouth Mid-Atlantic discontinuities the Foxal., ( et al., (1991), foret Carbotte example: Previous ridgeaxes.active particularly from away of their clearerte the revealing VGG,details thus Picard et al., 2018). This consists kmof ~consists etPicard 279,000This al., 2018). MalaysiaCh Republic the Australia, People'sand of FlAirlinesmissingMalaysiaforpart of the search effective elastic thickness of effective(T the lithospherethickness elastic We assess SSP date.these use morphologydata to to mapped two SSPs,off-axis fortuitously path providi d Ocean Indianof A Southeast these (SEIO). portion swath ~180 that sub-pa runs km central alongawide complex history of propagation. Note the units ofE complex units history Note of the propagation. morphology highpropagators showsof the resolution in (e) the is region shown bathymetryshipboard in are Identifiedstudy are in(c).SSPs of shown this FeaturesIndianSoutheast yellowRidge. lines trace moreconfid a SSPs allows clarity for extra and the study). reduced nois Note in this the significantly Figure 2. them in conjunction with satellite-derived free-air them with in conjunction

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article In this study, we make use makeof available wea In study,publicly use this Multibeam sonar data provide higher-resolution deta Multibeamhigher-resolution sonar provide data Multibeam2.2 bathymetry Comparison between (a) VGG v16 (used by etMatthews (used (a) VGGv16 between Comparison E ) associated theseanalyzing features by with ) 1991), and Grindlay et al. (1991), who et analyzed who (1991), al. Grindlayand 1991), e level severalreveals previously unidentified e ctonic histories. However,such histories. data are scarce, ctonic shown in availablein (d)and lines, shown as red gravity anomalies. anomalies. gravity ight 370 (MH370) by the Governmentsof (MH370)ightthe by370 2 2 ent identification of the traces of others. Thetraces entidentification of the of others. studies near the ridge axis those nearinclude studiesof, axis the ridge (Cochran and Sempere, 1997). Shipboard data (Cochran Sempere,and identified in identifiedetin Matthews (2011) al. DZs) (as ötvös = = 10 ötvös of multibeam concentratedbathymetrydata (MAR); Sempéré et al., along(1993), et the Sempéré al., (MAR); which we consider SSPs),ofconsiderwhicha section along we ng the best record of off-axis SSP off-axis ng of the best record ina (2017) (Geoscience Australia, 2017; (Geoscience Australia,ina 2017; (2017) nd Zheng et al., (2019), who analyzed the who (2019), Zhengndal., et rallel to the Australian plates flowline in in the plates rallel tothe flowlineAustralian ata are shown in Figure 3, the where searchata are shown in morphology as well as determine the morphologyas well as near the ridge, and satellite datashows ridge,neara satellite and the l. (1997) along the Southeast Indian Southeast the along (1997) l. multibeam dataset, recently acquiredmultibeamas recentlydataset, ils of SSP morphologyofSSP to ils compared -9 s -2 . . al., (2011)) and (b) v29 v29 al.,(used(2011)) and (b)

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article to to their flanks. relativekm~amplitudes 1 to up km wideare~with 10-15 theSSP bathymetric depressions Note thein (a).locations shown zonematch letter labels The (SZ). pseudofaultsaandsheared (PF) morphology of the two outer gross profiles showing the (a)(b) Bathymetric box). (red globe ofinset the location shows theTheprofiles shown in (b). triangles of thelocations indicate White propagation direction. following reversalin a shearedzone (SZ theouter pseudofault (PF capturedonlynorthernmostSSP mappedof the Mapping region. the to the shallowest depth within with relativeagetrendand plotted remove deepening the regional these to detrendedbeen data have respect their surroundings, to with morphologySSPs of the 2017).the tohighlightNote, (GA,for missing flight MH370 Indiansearch of asOceanthe part SSPs in the Southeast collected bathymetryoff-axis over two Figure 3. pseudofault (PF revealssouthernouter SSP both section,while mapping the of (a)Multibeam

1 ) and subsequent ) subsequent and 1 ), which formed ), which 2 ) overprinted by other bathymetric fabrics (e.g. Figu fabrics (e.g. overprinted other bathymetric by the of sediments suppressedbyand the accumulation is particularly This features located afor problem off- fossil SSPs located Figure for However, 4e-g). For can befrom axis. the which SSPs, traced active and be hadouter pseudofault sheared zone) to ident axes of th centralalongwe the therefore digitized arealway Figure bathymetricvalleysthey 3), (e.g. which are most in the of SSPs located (185 pairs), Weadditi VGG maps. modified an identify new to fit Matth pairs)by (112 We identified use features 224 threversals in polarity andmore SSP subtle traces the improvement in the qu made, originalwere picks “seesawanwe feelis propagator” features exhibit, temporaloftheetcomplex Zheng 2019). al. Because interpretedpropagatandbeen as simply NTDs called feature someand seen recentusenot literature, in “discor analysis, features were as classified these etof (Wessel al., 20 in the supplementalmaterials analyzingAn identical made al., VGG v16.(2011) by transforms which have clear fracture zone extension transforms whichclear have zone fracture San ridge/transformadhered to in the orthogonality in locations havepoints the ridge axis inflection Smith Sandwell (20 &bytraces previously published segmentsMOR incloseproxi also re-digitized those multibeamand available) bathymetry (whereearthqua free-airVGGgr including and the derived satellite 3. Results and Discussion 3. ResultsDiscussion and thousands of kilometers from the ridge axis (Figure ridge of axis kilometers from thousands the someand app thefound cases, ridges, nearthosein The ridge approximately s axis. symmetric about the and ridge prop like unidirectional discontinuities, yearsSSPs Figure 1). that are presenmillion (e.g. flips polarity that an component (“see with oblique trend d relativetheir They Eötvös surroundings. to

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article Our approach for digitizing SSPs followed two main main SSPs followed Ourtwo digitizing for approach We began our SSP cataloguing by modifying SSPourWe inter began cataloguing by the In order to catalog both active and fossil SSPs glo fossil SSPsInand both active to catalog order lows in the VGG, Eötvöst asSSPs continuous appear ofSSPs Identification3.1 digitization and of VGG lows. This required relaxingof the This VGG required lows. dant zones”. The “discordant zone” label has zone”label“discordant zones”. dant The agators, fracture zones and abyssal hills, are hills, abyssaland zonesfracture agators, on old on mayseafloor, signal old be the where al.have identifiedby(2011) et Matthews s ese lows. Second, both conjugate pairs Second,both esethe (i.e., conjugate lows. pairs tly "active” can be traced totheir associated betraced"active” can tly 15) as part of the GSFML database. In15) parttheir GSFML of as database. the at were previously unidentifiable (Figure 2).were unidentifiable at previously s expressed as local Eötvös lows lows in the VGG, expressedlocal Eötvös s as ominantly in the direction of spreading in the ominantlydirection but Atlantic and Indian and Atlanticbasins. Ocean avity anomalies (Sandwell et al., 2019),et (Sandwell avity anomalies appropriate and descriptive term. Since these appropriatedescriptive and re 4a-d). Where prevented re these ambiguities 4a-d). saws”) typically on timescales of a fewofsaws”) timescales ontypically axis, satisfyingcan axis, criterion this be difficult. ears as prominent as fracture zones, even as zones, fracture asearsprominent dwell &Smith study dwelland (2009) only ridge axis, there is little ambiguity there (e.g. here is little ridge axis, 4). 4). ifiable and symmetric about thespreading andifiable symmetric about ews et al. (2011), many of which wemanyews ethave (2011), al. s were included. were s included. mityfromSSPsfaults)(and transform to ignal of off-axis “fossil”similar SSPs to is ignaloff-axis of alitymanyrevealedhas data of the VGG and spatial propagation patterns these andpropagation spatial subsidence of the lithosphere and/or subsidence and/or lithosphere of the ing ridges (e.g., Dannowski et al., 2018; al., et(e.g., Dannowski ridges ing 09). Using the VGG grid,of 09). picks the VGG Using new our onal 146 146 onalfeaturespairs), total 370 a(73 for set of digitized features was alsoincluded was set of features digitized ke locations (Engdahl et al., 1998). Weal., 1998).et (Engdahl ke locations bally, we used a variety of data bally, of a used variety we rules: First,SSPs rules:create because ypically with amplitudes of ~20ypically amplitudes of with pretations of features etMatthews ofpretations features Figure4. fractureas as abundantSSPsbasins, are about 30% km.about 340,000 is theT samezonesbasins within SSPslengthdigitizedThe a bounds. of total the is ourand count the from SSPrela database. Thus, our conjugatew featurethe identification of or either along axial valley ( lows). alongmorphologies axial (VGG ridge symmetryoce in old can even beby their identified Atlantic. SSPs form South Indian,(d)in Southeast

(upper) SSPs in four (a) differentSouth SSPsbasins: P (upper) in here either trace was we unclear,tracethem was here omitted either bout 110,000 km;fracturelength bout 110,000 ofthe total pairs symmetric about the spreading ridge andspreading symmetricabout ridge the pairs anic crust. Virtually all activeoccur all SSPs anic Virtuallycrust. zones in the oceanic crust. zones crust. in the oceanic ted statistics may lowerconsidered ted statistics be hus, in the inthe intermediateslow hus,andspreading lower) Zoom of three areasalong spreading Zoomthree of lower) acific, (b) North Atlantic,(c)acific, North (b)

distribution peaks at 22 mm yr peaksmmdistribution 22 at ridges and fast ridges (> 40 mm yr40 ridges(>mm ridgesand fast segments. arepropagatingpresently ridgespropagators where distribution with respect with half spreading distribution to rate (b gl centroidon the polyline the segment sampled and computed SSP,of each time the of cent weformation ratealgridsMulleret globalof age spreadingand SSP newour discontinuity, transfor and analyzed we transformto seafloor respectfaults spreading with (Boulahanis et al., 2020). (Boulahanisal., 2020). et by mappi these identified have high-resolution been or ridgesareat subtleindistinguis spreading fast SimiHey1994;et(e.g. Cormier al., al., 1995).et fast-spreadingridgesa Pseudofaults al., 2019).at re less km) relief be wavelength cannot and/or (<12 upwardbat VGGdata.satellite to continuation, Due valleyat axial created thethe seafloorrelief in SSPs necessarilydoesn’t distribution suggest that axial the rangefrom transition in ridge topography ~largerthanlength whentheis segment30 offset torigimechanicalfrom that transition a non-rigid theinfe with is about thanconsistent Ma. 2.5 This i seesaw wethat lithosphere, propagation speculate 1991).et Since al., lithospheric depth-integrated e of other non-transformstudies (Macdonald offsets greater have offsetst transform age faults usually Figure are m SSPs a have shown distributions in 5b. restricted(SEIR),weRidgeIndian the Southeast th are fou SincespreadingSSPs active rate.primarily and ridge l measuredoffset SSP fault the transform

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article In order to better understand bet the Inrelationships understand to better order andratesSSPs Spreading3.2 ofage offsets To determine the distribution of transforma faults To determine the distribution -1 half-rate and drops to zero at both ultraslow (< 1 (

We investigate the detailed morphology andWe investigateisostati morphology the detailed SSPs of compensationMorphology 3.3 and isostatic )—in these environments (Southwest Indian ridgeIndianor these (Southwest environments )—in 1 (a) The distribution ofSSPs with to half distribution respect (a) The ), although the relationship is reversed (i.e. the (i.e. is reversedrelationship ), although the -1 is coincident with the transition from axial valle the from transition axial with coincident is 1 and SZ 1 ), as well as an additional outer as pseudofault wellan(PFadditional ),as outer rrents interact topography, internal with andrrents t multibeam analysis by Zheng et al.,we(2019),et Zheng multibeam by analysis t Mid-Atlantic Ridge and Southeast IndianSoutheastMid-Atlantic and Ridge. Ridge spreading rate only) (Small Sandwell,and (Small rate only) spreading the SSPs is about 30% of the length the fracture about of SSPs30% is of the fects internal tide generation remainsbe generation to internalfects tide ell developed. (b) Distribution of lithospheric of developed.Distribution ell (b) lion years,(green) whereas lion faults transform similarat that to oceanic zonesform fracture t both outer pseudofault valleys are ~valleys outerpseudofaultaret both 15–20 tt, 2003). How much SSP2003).muchtopography, tt, How front of the direction andfront of of propagation) the direction re where the bathymetric troughs of the SSPs bathymetric troughs where reof the f global seafloor roughness. Rough globalseafloorroughness. f seafloor morphology is also evident in the morphologyshearedalso evident is meters over age. They also exhibit also exhibit They over age.meters llected as part of the search for the missing the for of as the llectedpart search bathymetry for one complete “seesaw”bathymetryfor complete one today are less than about 2.5 Ma2.5 areabout which less thantoday ry has been detrended to removeeffect to the detrended beenhas ry see no SSPs at ultraslow ridges (< 10 ridges at(< ultraslow SSPs no see bathymetric highs occur on the younger occuron bathymetrichighs the spreading rate. The upper limit of < The limit rate.upper spreading c compensation of off-axis SSPsc compensation of off-axis the Arctic), neither theridgeArctic),neither the y to axial ridgeaxialy morphology to

2 ) difference in the effective elastic(effective differencethickness in the that olderis lithospheresomewhat (2-10Ma).This thereforand age faults offsets usually larger have locally crust is thanthinner compensated by normal between 0–30 km: betweenkm: 0–30 method using GMT (Wessel 2019)appetwhich al., method GMT we (Wessel using gravitythesatellite-de compared modelled with the Weapproa modellinga forward of adopted ~11–20 Ma. the~GeelwhileMa of (a)22–35 aage seafloor has Two plateareas elasticwere model. flexureselect andthe MH370 it expected anomalies bathymetry from thiTo plate test cools. with increasesage as the

from Tozer et al., (2019). fromal., (2019). et Tozer ~km the beyond 300 extendingperformedregions for Figu (a)(b)in andcoverage the within shown areas calculations(RMS) resmisfitroot-mean-square were Figure in the weretable as inset of outlined used, Forterms. calcu to four expandingthese the series the topography)(i.e.,Moho compensation using the gravityCalculate by the anomaly the produced bathy prescribedgiven bathymetry a load the Mohoplate,For topography acalculate uniform n=70). 571 km (degree ~km a ofthe (de datacut-offwavelength 400 using applied wereto spher &Moore,filters These 2017). mantle fully dynamicsco andfeatures,as deep such associatednotisostati fieldgravity which with is 2019)to remove al., the (Sandwelllon anomalies et Tozer filter(SRTM15+V2, e High-passthebathymetry Compute the RMS misfit between the calculated and o and misfitcalculatedComputethe RMS between the T e ), a proxy for lithosphere strength that usually proxy for that ),usually lithosphere astrength T s hypothesis, we modelled the the free-air gravity s hypothesis, modelled we e

e much of the topography is formedonmuch is topography ofe the value. ed (i.e., (a) and (b) in Figure 6); the SSPFigurearea the in ed (a) (i.e.,6); and (b) difference in age should be evidentashould difference as in age rived gravity. The steps below outline our below outline gravity. rived steps The (Zheng et al., 2019). In contrast,(Zheng et transform al., 2019). vinck fracture region (b) has ahas vinck(b)regionseafloorfracture age lied for a range of constant constant range of alied for s isostatic compensation s using isostatic a thin ch (e.g. Wattsand al., 2006), et ch (e.g. c compensation of the seafloor of compensationthe seafloor c 6. In order to avoid edge effects, theeffects,edge 6. avoid In to order lations, standard parameter lations, values re 6, while the calculations were rewhile the calculations 6, g fromthe component wavelength gree~taperedcosine to n=100) mpensated bathymetry (e.g. Wattsmpensatedbathymetry(e.g. ical harmonic representations of ical representations harmonic required to compensate for the to compensate required method of Parker (1973), (1973), method of Parker metry and its andisostatic metryits tricted to multibeam bathymetry to tricted se using predicted bathymetry bserved gravity anomalies.gravity bserved t al.,2019) and free-air t T e values are listed in the inset table ( are in the inset table listed Figure 6. mantle t density; calculated using the givencalculated using the RMS inset shows misfits box Themapmain box). (red Mulleret fromal., (Ma)(201 seafloor age contours (a)modellingandthe SSPs in the isostatic of Geel grid. VGG Red boxes 2017) regional overlainon the

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article Multibeam bathymetry acquired during the search fothe acquired during Multibeambathymetry c – crustal thickness; E – Young’s modulus; sigma E– thickness; Young’s – crustal – T ρ e values. Values for other physical parameters used physical values.parameters Values other for w – water density; water– ρ c – crustal–density; vinck Fracture Dashed vinck (b).lines = Zone 6). The globe Inset showsglobe of the TheInset location the 6). show the areas used for RMS calculations RMS for the areasusedshow for isostatic compensation modelscompensation for isostatic r missing flight MH370 missingflight (GA, r ρ f Poisson’s ratio; f Poisson’s ratio; – infill density; infill – for the modelling modelling for the ρ 1,2 m – filter– – – hypothesis using four prominent SSP traces along th fourtracesalonghypothesis SSP using prominent (assuming purel aridge symmetrical spreadingabout the just kinksin the nottraces,Moreover, b is it of be data usedtraces that new can type a provide Zone. We Zone. the interpret low

indicate the best-fit parameters). arrows The black value. value. best-fit tectoni ahasreflectinga minimum broadof mixture involves the flexure andl ofthe involves flexure older, hence stronger requiredfea compensationto maintainflexural this t Ma)—reflects (~a5 contrast much with age larger Incontrast, al., the (2019).valueacross the Geel mant crust thin and shallower with normal thus than ridge ax verylithosphere on the weak near and thin formation. Thatthes is, lithosphere the timeat of SSPs and 8 km for the Geelvinck Fracture Zone). NotFracturethe Geelvinck SSPs km Zone). and for 8 how abruptly it change. mayabruptlyhow it can easilyapproximat coordinate the we system, see easilyAdd soexplained. are incongruities not that S age-concurrent the eachsmall forcircle are path coordinate systemin this matchwell SSP deviations Mulleret fromal., the ageas of sampled the plate thefromSSP of deviation the of small trace circle fittingrangea of pol age forpole opening by that

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article The results are shown in the inset of FigureForof the inset are shown The 6. in results One of the important characteristics tha of SSPs One is of characteristics the important newdata for typeSymmetrySSPs3.4 and reconstr of T e for the SSPs of 3 km is significantly less th thansignificantlykm 3 SSPs for less is of the T e value for the SSPs as reflecting the “frozen-in” “frozen-in” s reflectingtheSSPsvalue as the for ut the overall shape ofthe the traces be that overall should shape ut vinck Fracture separates Zone—which seafloor vinck e features formed across a narrowacross a features discontinuityformed e e to a nearby fracture zone. We measuredto a zone. nearbyfracture the e (2016) age map (Figure 7). the The7). age of (Figure map (2016)shapes ithosphere, which is reflected in the whichlarger reflected is ithosphere, opening, and plotted this deviation the against plottedopening,and this itionally, by plotting these data itionally,in this plotting these by SP pair. There are, however, pair.some are, SP There to refine detailed plate reconstructions. refineplate reconstructions. detailed to

T ture (e.g., Sandwell &1982).tureSandwell Schubert, This (e.g., is. The is. bathymetric troughs are associated le in agreement with the of etanalysisin agreementZheng le the with he averaged signal of the time-dependent time-dependent he averaged of signal the c processes in each region. eachNevertheless, the cregion. processesin —which verifies that the “excursions” from that the —which verifies e e rate of propagation along a ridge axis and ridgeaxis a propagation ealong rateof e SEIR. y symmetric spreading). We spreading). y tested this symmetric values for each region (i.e. 3 km forkm3 each the (i.e.valuesregion for e the units of Eötvös = 10 e= of the Eötvös units both areas, the RMS misfit versusareas, misfit both the RMS t the symmetrickinksin theirt off-ridge e 8 km for the Geelvinck Fracture ekm8 the Geelvinck for

Forawe eachapproximated pair, uctions trength oftrengththe -9 s -2 . T T e e

propagation direction are marked as arrows above th arrowsabove propagationdirection are marked as testing studyforhypotheses. of qualitative these Figure SSPs behaviorin that are testable. shows 8 theseImportantly,woul of together. each processes are These 1985).hypotheses Morgan Parmentier, and volcanism hotspot (Heypropagationinresponse & to of or asthenos resultas a Morgan 1994) &Sandwell, downtop a Lonsdale, 1985) regional propagation (2) large-scalein responseof change the to ridge axis merecently these reviewed al.,Dannowski (2018) et Figure7. relatively wide sheared zones. zones. relatively wide sheared grid, asymmetric errors spreading, in the age small th reveals match the the ridge deviations across of morphologyclear).Location sense ofis noroffset thesheared di (no zone and dashed line a indicates line indicates solid A Plate a). for Plate (African the to smallrespectcircle spreading of with plate

Several hypotheses have been proposed to explain un explain beenSeveral to proposed have hypotheses AssessmentSSP3.5 propagation models of FourIndiaSSP pairs in in the Southeast prominent the outer pseudofault branchof the the segment,outer pseudofault SSPs that intersect the ridge and thearidgehave SSPs clear that intersect age (red – Australian Plate, Antarctic Plate, –ageblueAustralian–(red s in plate motion (e.g., Hey & Wilson,motion s in plate &(e.g., Hey1982; eirMismatches duemay symmetry. to be the South Atlantic and uses this basin caseas a this the South andAtlantic uses maps for the SSPs are shown The in (e-f). SSPs mapsare shown the for made is wherestinction the forneither (c) and/or errors in identifying the center of thetheof center errors and/orin identifying d produce predictable patterns in SSP produced in predictable patterns e profile plots (Figures 8b-d). e profile(Figures plots chanisms, which include: (1) chanisms,reorientation which include: pheric flow (West et al., 1999); andpheric 1999); (3)et (West al., flow ography or gravity gradient (e.g. gradient gravityPhipps- ography or Vogt, 1977; Hey et al., 1980; Phipps- 1980; et al., Hey1977; Vogt, not exclusive and they are often invoked are often they and exclusive not idirectional ridge propagation. idirectional ridge propagation. n Ocean and their deviation from deviation their and Oceann

changes(Lonsdale, conversely,theaway from and, spreading direction ofpropagateplate should toward the uniformlypole along a givenchange is alongthe a pole isochrona s since spreading axial magma system beneath a system of ac systemmagmaspreadingaof beneath axial system must hypothesisthis chambers.testing Ultimately, ontime,this atcannot, comment weconceptual,and curvature slow-spreadingseevalleys, we high axial ofridgeto thespreading Moreover, curvature local “pulses,”may magmaofth producing be capable they De representing local upwellings. daymagma present arefrom ridge nearaxis propagatinglocal away the Figuremagma sh foci.propagationthe away 8a from Martinez1997;H andTucholke 1995; al., et et al., (e.g.materialmagmafromSem transport a of source a dynamic delivery magmato mayas a occur response mor mechanism drivingscalea onlocal operating is beh forcapablealone, not of the accounting seesaw distribution of changes throughdistribution (Figure 8f). time (e.g.eventsLonsdale, around plate reorganization propagation whereof points”changes thedirection along propagationdirection Additionally the ridge. observed of activethe al explain SSPs distribution propagation, which is not observed. observed. propagation, whichis not Westas in flow,et asthenospheric al., (1999) such the processof primarystylenot of this driver is i of examples activethere propagation are numerous regionalSSPs theactiveandbetweenbath currently the direction arrows show ofand as blackdots the are shown as red axis curve thebathymetryridgeat gainat 0.5 sh 160 bathymetry km with as wavelength hypothesis, wethis low- gradient.gravity To test by these features are also unlikely d features by also to be primary these are tothe sca SSPs widespreadrelative of distribution activity rulehotspot an influence propag out of on marked areas blackd Three South hotspots Atlantic

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article Hypothesis (1) predicts that when there is awhen predicts change Hypothesis that is there (1) Hypothesis (2) predicts that all the propagatorsall mo predicts the Hypothesis that (2) Hypothesis (3) predicts that the propagators move a move the propagators predicts Hypothesis that (3) We conclude that the processes proposed to explain explain We theprocesses to concludeproposed that

1985), such that, the direction of that, propagation woulsuch the direction 1985), ridge propagation. Propagation bydriven ridge propagation. pass gravityfiltered both thethe and pass rivers in most cases. rivers in most cases. ation entirely,ationbe from can the seen it rce existence of hotspots, that that generatedforces rce existence of hotspots, , has a similar pattern of regionally coherent ahaspattern , similar of ong the MAR, which show manyMAR, reversals in ong the which show imple function of age.functionimple of ey, 2017; Dannowski et al., 2018) causes ridge al., 2018) et causes ey, Dannowski2017; 1985) 1985) moreinstead randomand a see propagation. There is no clear correlation clearcorrelation no propagation. There is , we have estimated ages at“inflection SSPestimated have ages we , involve ainvolve dedicated slow- of 3D imaging maypography processes.reflect At these s in Figuremarked are propagators s in The 8b,d. positive anomalies, which we interpret as we interpret anomalies,which positive in general. However, this remainsgeneral.purely However, in this Itappears that avior thereforea of SSPs. and found no clustering of these andchanges clustering found no pole of opening during anticlockwisepole opening of during ymetric Moreover,gradients. gravity and rotation during clockwise changes during rotationin clockwise e likely. We likely.SSP e speculate propagation that ots in Figure to difficult it Although8a,c.is in ots n the up-gradient direction, suggesting the n up-gradient this direction, the true nature of sub-axial magma nature the oftrue sub-axial pere et al., 1993; Michael et al., 1994; al., Gente1994; Michael et pere al., 1993; et own in Figuregravity filteredin andownThe 8a,c. pending on the time scales of onsuchscales pending the local time ows that several, but not all, activeall, owsthat not SSPsseveral, but tive SSPs. SSPs. tive e propagation patterns we observe. patterns e propagation system, in which, complex upwardwhich,complex in system, ve down a regional vedowntopography aor regional in plate motion, all active ridgesin plate active motion, all way from the upwelling hotspots. hotspots. wayupwelling from the unidirectional ridge propagation ridgepropagation are,unidirectional d be the same for allsame SSPsbe dthe for

Clearly this doesthis not Clearly Figure8. indicated changes in propagation direction or major propagation direction or changesindicated in Withingrid SSPs. al., t (2016)and age interpreted asbathy d) (a-b) Same low-pass except filtered for ofSSP intersection points propagationdirection at versus r SSPs distance Thealong (black). (b) depth

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article (a) Low-pass filtered gravity anomaly with present gravitywith anomaly(a) Low-pass filtered his region, we selected points on SSPs on region,his points that selectedwe s and the ridge are shown arrows. by(c- the s ridge and small are shown metry (Tozer et al., 2019). (e) The Muller et(e)(Tozeral., The 2019). et metry idge shows regional gravity gradients,theand regionalgravity idge shows change in rate and on sampledrate change these points in -day ridge axis digitizedand(gray) -day axis ridge

their formation and behavior. We the following drawtheir behavior. andformation nature and with to tectotheirrespect distribution Acknowledgments, Samples, and Data Samples, Acknowledgments,and Data 2019) can be found 2019) at canftp://topex.ucsd.edu/pub/srtm be andftp://topex.ucsd.edu/pub/global_grav_1min/, the Conclusions 4 crust. ofSSPs propagatandselection conservativeour the changes time, clustering bu with the propagation of of these c distribution Showsgrid. the the age (f) found found at and to generate figures. The latest vertical gravitgeneratelatest Thevertical toand figures. 2 et(Wessel, Mappingal., Tools 2866).Generic The OfficeandNa of the (NNX16AH64G) NASAprogramSWOT of helpedthepresentation thi focus and improveus W the altimeter datasets.raw on all data waveform found found at

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article ● ● ● ● ● ● The authors thank ESA, NASA, ISRO and CNES theNASA,forCNES and ISRO The thank authorsESA, In this study we have documented the globaldistrib In documentedstudy we the have this https://www.aviso.altimetry.fr/en/data/products/sea https://science-pds.cryosat.esa.int/

fracture zones within the intermediateslow andfracturespr within zones lengthseesaw i total propagators identified of the time of formation of the given SSP pairs. givenofSSP thetimepairs. of formation must themeet ripoints at reconstructions as these usedSSPs canofto im be reversefossil direction) thein axes, ridge about Because SSPs are symmetric young hot,ne onlithosphere confirming formed they fossil SSPsfound wasThe thickness elasticof two morphologyyounger This mirror side. towards is the steep the older with onsideof outerslopes pseudo thesurrounding to respect km1-2 seafloo with deep W-shaped in Seesawbathymetric results propagation “non-rigid”for weakSSP allows lithospherebehavio t Ma.a~ thanThis reflects likelyrheological 2.5 wit almostSSPs form discontinuities exclusively at (i.e.,spreading intermediatehalfridges spreading phenomenon ubiquitous is a Seesaw ridge propagation produce SSPs (e.g., Zheng et al., 2019). al.,2019). ZhengSSPs produce(e.g., et the may temporal in magmavariations supply provide WeSSP for sp accountbehavior. unabletherefore to unidirecti to explain Processes previously proposed . Jason-1/2 and SARAL/AltiKa waveform andbe SARAL/AltiKa Jason-1/2 can .data y gradient products can be foundat be gradient yproducts can nic setting and tested mechanisms to explain mechanisms settingto explain tested and nic hanges through time. There isn’t an obvious There isn’t time.an through obvious hanges s work. This work was supportedwork. by s wasthe This work t there is a noticeable decrease—this is due to to is duethere noticeable decrease—this t is a e extend our thanks to the the reviewers who to thanks our extend e 15_plus/ in older as changesclear ion aren’t which SRTM15+V2 bathymetry (Tozer et al., al., bathymetry(Tozer SRTM15+V2 et 019) were used extensively in data analysis 019) analysis extensivelywere usedin data conclusions: conclusions: ution of analyzedseesawution propagators, hreshold, whereby only youngand only hreshold, whereby -surface-height- . Cryosat-2 waveform data can be .data waveformCryosat-2 can be s aboutof ofthe 30% total s length rates between 10-40 mm yrmmbetweenrates 10-40 dge axis when reconstructed to the when reconstructed dgeaxis prove the accuracy of plate the ofproveaccuracyplate faults and faults broad slopes shallower eading basins. basins. eading to be km) to very low (~ 3 h lithospheric age lithospheric contrasts h less onal ridgeonal appear propagation val Research (N00014-17-1- Research val r. areasymmetric These valleys eculate that local spatial andeculate spatial that local flection points (whereflectionthey points ed for the sheared zones. zones. theedsheared for ar the ridge axis. ridgeaxis. the ar r (Grindlay et al., 1991). (Grindlayret al., 1991). valleys ~ 10–20 km wide and ~ kmand ~valleyswide 10–20 open policy and tothe accessopen policy driving forces required to to drivingrequiredforces that occurs at slow andat slow that occurs -1 ).The Dannowski, A., I. Grevemeyer, J. Phipps Morgan, C. I.Morgan, A.,PhippsDannowski, J. Grevemeyer, Dannowski, A., Morgan, J. P., Grevemeyer, I., &Ran Morgan,I., J. A., Dannowski,P., Grevemeyer, Cormier, M.H., Macdonald, K.C., Pacifi East (1994).Macdonald, M.H.,Cormier, Chen, Y. J., & Morgan, W. J. (1990). Rift Valley/No Rift(1990).W. &Morgan, J., Y.Chen, J. products/global/waveforms.html Boulahanis, B., Carbotte, S. M., Carbotte,P.B., Ne S. J., Boulahanis,Huybers, References https://portal.ga.gov.au/persona/marine. Engdahl, E. R., R. VanderHilst, and R. Buland (199 andEngdahl,Buland R. VanderHilst, E. R., R. Lithospheric Structur and A.R. Dunn,Crust (2015). Carbotte, S., Welch, S. M., & MacDonald, K. &MacDonald,(199 Welch,M., C. S. S., Carbotte, Carbotte, S.M., Smith, D.K., Cannat, M. and Klein, Smith,M.S.M.,andCarbotte, Cannat, D.K., Briais, A., & Rabinowicz, M. varia Temporal (2002). Briais, A., &Rabinowicz, Cochran, J. R., &Sempéré,(1997).Cochran,C.Southe J. TheJ.R.,

This article is protected by copyright. All rights reserved. ThisAllarticleis rights by copyright. reserved. protected Accepted Article https://doi.org/10.1007/BF02428195 https://doi.org/10.1007/BF02428195 and 31°-34°30 fracture zone offset histories during the past 5 my during the fracturepast 5 histories offset zone Crustal structureridges Crustal of the propagating TAMMAR 543–564 543–564 axialmigrationby of ridge reorientation ultrafast Geophysical Research: Solid EarthGeophysicalSolid Research: Geophysical Research: Solid EarthGeophysicalSolid Research: supply? A test using crustal thicknessbathymet and usingsupply?crustal test A Do (2020).inf variations seaLangmuir, level H. C. altimetry data. altimetrydata. Earth and PlanetaryLetters and Earth Science 4.00011-7doi: 10.1016/B978-0-444-53802-4.00011298- 4.00011-7doi: 1).(Vol.Retrieved Elsevier B.V. fromhttp://dx intermediate spreading intermediatemid spreading 21.5°N, Geochem. Geophys. Geosyst., 12, Q07012, doi Geosyst., 21.5°N, Geochem.Q07012, 12, Geophys. the Death of a Transform Fault: The Mid-AtlanticFault:Ri The the aDeath Transform of Ocean Propagation, Segment Upwelling/Melting Caused https://doi.org/10.1002/2017JB014273 https://doi.org/10.1002/2017JB014273 Gravity anomalies and crustal accretion ataccretion Gravitycrustal intermed andanomalies 1 95(B11), GeophysicalRidges. Research, of Journal Am., 88:722–743. Am., 88:722–743. forimprovedand with depth procedurestimes travel Society, London, Special Publications,London,Special Society,pp.2 420(1), asy System: RidgeOcean segmentation of the Global ′ S. Journal of Geophysical Research: Solid EarthSolid of GeophysicalJournal Research: Marine GeophysicalMarineResearches . MH370 search bathymetryat can found MH370 be search . ‐ ocean ridges 1. Synoptic observations based on sate observations based ocean 1. Synoptic on ridges , , , , , 123 102 535 (2), 941–956. (2),941–956. 15463-15487.(B7), , 116121. 116121. , dimovi E.M., (2015). Tectonic magmatic andE.M.,Tectonic (2015). e - SeismicRidges Structure Mid-Ocean e - of 8). Global teleseismic earthquakerelocation Globalteleseismic8). ast Indian Ridge between 88 andE Indian88 118 E: between ast Ridge Rift at Valley Rift Mid- Ocean Transition c Rise 18–19S: asymmetric spreading and 18–19S: c asymmetric Rise spreading tions of the segmentation of slow slow to of of the tions segmentation R. Ranero, M. Maia, and G. KleinRanero,G.and(2011).R.M. Maia, 1). Spreading rates, rift rift propagation, 1).and rates, Spreading ero, C. R. (2018). Enhanced Mantle(2018).ero,R. C.Enhanced on the Mid-Atlantic Ridge; theMid-Atlantic25°-27°30on Ridge; , , discontinuities. J. Geophys. J. discontinuities. Res.99, .doi.org/10.1016/B978-0-444-53802- 13 ć luence mid-ocean ridge magmaridgemid-ocean luence , M. R., Aghaei, O., Canales, J. P., &M.J. O., Canales, P.,Aghaei, R., , iate spreading rates. 49-295. 49-295. ry PacificEast Rise.from the data (1), 51–80. (1), 51–80. determination. IBull. Seismo. Soc. IBull. Seismo. Soc. determination. dge21.5°N. at 7.571–17.581. 7.571–17.581. nthesis of observations. Geological of observations. nthesis egment on the Midegmentthe on :10.1029/2011GC003534 :10.1029/2011GC003534 ic Core Complex Die Off, and Off, Die Core Complex ic 7 7 , 107 (B5), ECV-3. ECV-3. (B5), Journal of Journal Journal of Journal ‐ Atlantic Ridge,Atlantic llite llite ′ S Johnson, H. P., Karsten, J. L.,J. P., Karsten,Delaney,H.DavR., Johnson, J. Hey, R.N. and D.S. Wilson Propagating(1982). rift and Hey, D.S. R.N. Hey, R.N. and P.R. Vogt (1977). Spreading center jucenter(1977).VogtP.R.and Hey, Spreading R.N. Grindlay, N. R., Fox, P. J., & Macdonald, K.&Macdonald,C. Fox,P. (19 J., Grindlay, R., N. Raw1 2017. SearchPhase MH370Geoscience Australia Garrett, C. (2003). Internal tides mixing and(2003). Garrett, C. ocean Hey, R.N., P.D. Johnson, F. Martinez,F.Korenaga, J. Hey,P.D. Johnson, R.N., & S.,T.,Atwater,Kleinrock, Miller,Hey, M., R., Fox, P. J., Grindlay, N. R., K. &MacDonald,(19 C. R., N.Fox,P.Grindlay, J., Karson, J. A. (1986). Lithospheredepth st age,Karson,andA. J. (1986). Hey, R. (1977). A new class of ”pseudofaults” and t and of ”pseudofaults”Hey, class A(1977). R. new Hey, R., Duennebier, F. K., & Morgan, W.F.K.,&Morgan,J.Hey, (1980). Duennebier, R., Korenaga, J. and R.N. Hey (1996) Recent dueling pro (1996)dueling Korenaga,HeyRecentand J. R.N. A.,&Orcutt,J.G., Harding,Kent,Evidenc (1990). Hey, R. (2001). Propagating Rifts and Microplates.Propagating Hey,and(2001). Rifts R. Langmuir, C. H., Bender, J. F., J. (1986) Langmuir,&Batiza, R. H., Bender, C.

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