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Boris J. P. Kaus coauthored three-dimensional models testing how transform fault stresses affect adjacent detachment fault formation, beyond a simple weak-boundary explanation.^[ref]

The seafloor continuation beyond the actively slipping ridge-to-ridge transform fault. Its two sides can differ in age without continuing relative plate-boundary slip.

Garrett Ito coauthored a study of how magmatism and transform fault stresses influence the asymmetric formation of detachment faults near slow-spreading ridges.^[ref]

Jana C. Schierjott coauthored three-dimensional ridge-transform models that favour excess lithospheric tension from transform fault shear as an explanation of asymmetric detachment fault formation.^[ref]

John Tuzo Wilson introduced transform faults as a distinct type of boundary needed to connect seafloor spreading and other relative plate motions. Where two spreading-ridge segments are offset, active sliding occurs on the connecting part of the fracture; its continuation beyond a ridge can separate crust moving together and need not remain an active plate boundary. The geometry predicts a slip direction that cannot be inferred merely by treating the offset ridge as a formerly continuous line. His 1965 proposal made a structural pattern into a test of plate tectonics.^[ref]

A geophysicist associated with transform faults and the Wilson cycle.

Hawaii: short-wavelength volcanic loading and long-wavelength mantle support must be distinguished. A dense volcanic edifice replacing seawater adds mass and gives a positive free-air gravity anomaly. Its load bends the lithosphere down, producing a surrounding moat and an outer flexural arch. The associated displaced density interfaces contribute negative and positive gravity signals at neighbouring distances. Observed gravity near the Hawaiian ridge includes strong positive anomalies over the ridge, negative flanks, and a broader positive belt. At much longer wavelengths, the Hawaiian swell also correlates with a positive gravity anomaly, with a smaller gravity-to-topography ratio that requires compensation; the precise source of support is not determined by that correlation alone.^[ref]

The mechanical distinction can be expressed with a simple elastic-plate model. For load height $h$, downward deflection $w$, plate rigidity $D$, loading density contrast $\Delta {\rho }_l$ relative to water, and restoring density contrast $\Delta {\rho }_b$ at an interface,For a Fourier component of horizontal wavenumber $q$, this gives $w_q=\Delta {\rho }_{l}g{h}_q/(D{q}^4+\Delta {\rho }_{b}g)$. The load's direct gravity contribution competes with the negative contribution of a depressed interface at reference depth $t$. In a linear thin-interface approximation,At short wavelengths rigidity suppresses compensation, leaving relatively high positive gravity admittance. At long wavelengths the plate can deflect and compensate more completely, reducing admittance. Fitting the wavelength dependence constrains effective elastic thickness through $D=E_Y{T}_e^3/[12(1-{\nu }^2)]$, subject to density structure, load distribution and subsurface loading assumptions. This explains why local Airy compensation alone misses the spatially extended flexural response.

The broad swell needs a deeper explanation than the narrow volcanic pile: hot, buoyant mantle and mantle flow can support regional topography, while deep density anomalies and surface elevation jointly determine its gravity. A free-air anomaly keeps the attracting mass of the topography; a Bouguer correction removes an assumed direct topographic attraction and can reveal its compensating mass deficit. Gravity plus topography constrain support as a function of wavelength; neither alone uniquely fixes the mantle density distribution.

For the OR alternative, triple junctions are points where three plate boundaries meet. Each boundary can be a spreading ridge, subduction trench, or transform fault. The three plate velocities satisfyThis velocity triangle is necessary but not enough: a single junction velocity ${\mathbf{u}}_J$ must also keep the meeting point on all three moving boundaries. For symmetric spreading between A and B, the ridge constraint is $[{\mathbf{u}}_J-({\mathbf{v}}_A+{\mathbf{v}}_B)/2]\cdot \mathbf{n}=0$. For a transform, ${\mathbf{v}}_A\cdot \mathbf{n}={\mathbf{v}}_B\cdot \mathbf{n}$, and the junction must have that same normal component. For a trench, its normal migration must match the adopted subduction/rollback model; a trench fixed relative to the overriding plate shares that plate's normal velocity.

In velocity space each boundary supplies a line of possible junction velocities. A common intersection means the junction can migrate while preserving its local configuration; incompatible constraints force boundary reorganization. This is kinematic stability, not the claim that the junction is stationary. A symmetric ridge–ridge–ridge example has three arms meeting at $120^{\circ }$ and a common junction velocity; unequal spreading rates do not require those equal angles. Transform and trench junctions depend on the allowed relative motions and boundary geometry. Stable and unstable evolution were formulated through plate-velocity geometry in the original triple-junction analysis.^[ref]

These original diagrams show an illustrative flexural response and a symmetric ridge-junction construction; they are not maps or measured Hawaiian profiles.

At latitude $\varphi$ and longitude $\lambda$, $\mathbf{r}=R(\cos \varphi \cos \lambda ,\cos \varphi \sin \lambda ,\sin \varphi )$. Motion is ${\mathbf{v}}_{B/C}={\mathbf{\omega }}_{B/C}\times \mathbf{r}$. A meridian boundary has horizontal normal ${\hat{e}}_{\lambda }=(-\sin \lambda ,\cos \lambda ,0)$, so its across-boundary velocity isFor a transform fault this must vanish along the whole meridian, not only at an isolated point. Thus $5\cos \lambda +12\sin \lambda =0$. Select the solution in the western hemisphere:The other solution is the antipodal meridian in the eastern hemisphere. Geometrically, the transform meridian is in a great-circle plane perpendicular to the Euler angular velocity vector. Its outgoing tangent direction at either pole, expressed in the fixed $x,y$ axes, is ${\hat{t}}_F=(12,-5)/13$.

At the south pole $\mathbf{r}=-R\hat{z}$. Choose plate C as the instantaneous reference frame. Since $R=4\times 10^9$ mm, the two components of relative angular speed give 20 and 48 mm/year. The plate velocities in the fixed tangent-plane axes areThe plate velocity triangle therefore has sidesThe physical boundary rays point along $+x$ for AB, $+y$ for AC and $(12,-5)$ for BC. Plate A occupies the quadrant between the first two rays, B the narrow wedge between AB and BC, and C the remainder. The stated overriding relations make AB and AC subduction trenches, while BC remains a transform fault: this is a trench-trench-transform triple junction. Put the subduction teeth on B's side of AB and A's side of AC, identifying B above A and A above C.

For kinematic stability there must be a single junction velocity $\mathbf{U}$ compatible with all three boundary-normal motions. Use the standard idealization that each trench's normal velocity is that of its overriding plate, with no independent rollback. AB is parallel to $x$, so $U_y=v_{B,y}=20$. AC is parallel to $y$, so $U_x=v_{A,x}=-48$. The transform requires $\mathbf{U}-{\mathbf{v}}_C$ to be parallel to $(12,-5)$, which is true for this intersection. HenceThe southern triple junction is instantaneously kinematically stable. It is stationary relative to B, migrates along AB relative to A, and migrates along BC relative to C. This compatibility result does not promise long-term stability if plate rotations or trench rollback change. Notice that the three relative velocities close even though the overriding order is not a statement that all three plates move toward one common stationary point.

The decisive change was from moving continents within a supposedly permanent ocean floor to moving coherent tectonic plates that include both continental and oceanic lithosphere. Several independent observations made that change testable.

Continental connections supplied the initial problem. In the early twentieth century, Alfred Wegener assembled matching continental margins, correlatable rock belts and mountain chains, shared fossil assemblages, and paleoclimate indicators into the case for continental drift. Reassembling Gondwana, for example, makes geographically separated glacial deposits and striation directions compatible with one ice-sheet system. Fits at the continental shelf edge are physically more meaningful than exact fits to modern coastlines, which have been modified by erosion and sea-level change. The evidence suggested relative movement, but did not justify the proposed forces: continents cannot readily plough independently through strong oceanic rock. A convincing mechanism and independent motion measurements were missing.

Oceanography changed the boundary conditions. Echo-sounding surveys revealed a connected spreading ridge system, axial valleys, subduction trenches and long fracture zones. Seismic refraction surveys established systematic differences between continental and oceanic crust. Thin oceanic sediment cover, high ridge heat flux and the lack of very old exposed oceanic basement made permanent, ancient ocean basins increasingly implausible. Harry Hammond Hess proposed creation of oceanic lithosphere at ridges and recycling at trenches: seafloor spreading without requiring an expanding Earth. Slow mantle convection supplied a physically plausible connection between surface transport and internal heat loss. The mechanism need not have been completely quantified before its kinematic predictions could be tested.^[ref]

Magnetic records supplied a clock and a speedometer. Dated continental lavas established a sequence of geomagnetic reversals. Marine magnetometers then found elongated, approximately paired marine magnetic stripes on either side of ridges. The 1963 interpretation by F. J. Vine and D. H. Matthews combined repeated reversals with seafloor spreading: cooling basalt locks in remanent magnetization, and continuous motion converts a time sequence into a spatial sequence. If a polarity interval lasts $\Delta t$ and occupies width $w$ on one ridge flank, its half-spreading rate is $w/\Delta t$. Matching several reversals tests the predicted sequence, rather than merely fitting a single stripe.^[ref] Different apparent polar wander paths for different continents also became mutually consistent after continental reconstruction, favoring relative continental motion over independent magnetic-pole histories.

Earthquakes identified creation, translation and consumption. Improved global seismology located shallow earthquakes along ridges and transforms, and dipping Wadati-Benioff zones beneath trenches. Their progressive focal depths identified cold, coherent slabs entering the mantle. Focal mechanisms showed extension at spreading boundaries, tangential slip at transforms and convergence at trenches. In 1965, John Tuzo Wilson's transform fault interpretation made a particularly discriminating prediction: active slip occurs between offset ridge segments, with a sense that can be opposite to that inferred by treating the entire lineament as an ordinary offset fault. The outer fracture zones are inherited traces, not continuing active plate boundaries. Agreement of focal mechanisms with the transform prediction linked magnetic and seismic evidence.

The late-1960s synthesis made these observations one quantitative theory. Relative motion of rigid tectonic plates on a sphere can be described by an Euler angular velocity vector, with $\mathbf{v}=\mathbf{\omega }\times \mathbf{r}$. Spreading rates, transform azimuths and slip directions must fit the same rotation, and relative angular velocities must close around plate circuits. The resulting framework accounted for global boundary geometry and earthquake mechanisms without moving continents separately from the seafloor. Deep-ocean drilling beginning in 1968 subsequently confirmed that basement and overlying sediments generally become older away from ridges; this was a powerful confirmation of an already emerging synthesis, not a prerequisite discovered decades earlier.^[ref]

Thus plate tectonics succeeded through agreement between geological reconstruction, magnetic chronology, ocean-floor structure, seismology and rigid-plate kinematics. Modern satellite geodesy verifies motions directly, but belongs to the later confirmation of the theory, not its original 1960s evidence.

A lies on the continuation of the offset outside the two ridge tips: it is the fracture zone, whose two sides are carried in the same overall plate direction. A bathymetric step can remain because the two sides have different ages and thermal histories, without continuing plate-boundary strike-slip faulting.

B is the black segment connecting the two white spreading ridges. Construct the plate motion from divergence away from those ridge axes. Between their tips, the upper side of B belongs to the plate west of the right-hand ridge and moves approximately west-northwest; the lower side belongs to the plate east of the left-hand ridge and moves approximately east-southeast. Looking across B from either side, the opposite side moves to the observer's left. B is therefore a left-lateral strike-slip faulting on a transform fault. The offset preserved outside the active segment must not be read as the sense of present slip.

The grey arrows in the source image are pointers to detachment faults, not plate-motion vectors. The original publication identifies white lines as spreading ridges, black lines as transform faults, and arrows as pointers to detachments. Its Figure 1b is the unlettered source of the exam's Figure 3.^[ref]

C lies on the white spreading ridge extending down from the left-hand ridge-transform intersection. Relative motion there is extensional, so its tectonic faults have normal slip. Dike intrusion also accommodates extension at a spreading ridge; “normal slip” is the appropriate category among the four offered, not a claim that all spreading is achieved by a single normal fault.

Probably yes in connected fractures or transiently opened pore space, especially where a transform fault admits circulating seawater; a uniform water-filled porous layer several kilometres thick is not guaranteed. Porosity and permeability of a porous medium generally decrease as cracks close or seal, while ongoing faulting can reopen pathways. Fluid can occur at high pressure and temperature, including a supercritical state; it need not resemble cold surface water.

Several complementary tests address presence and origin:

No one anomaly uniquely identifies water. Seismic velocity can also reflect cracks, composition and temperature; electrical conductivity can reflect melt or conductive minerals. Serpentinization demonstrates incorporation of water into minerals, which must be distinguished from fluid currently occupying pore space. At an oceanic transform fault, an external seawater supply is the natural first hypothesis, but isotope ratios and chemical budgets can test contributions from deep fluids rather than presuming the source. A research example of coupled deformation and hydrothermal alteration is Mass transfer and fluid flow during detachment faulting and development of an oceanic core complex, Atlantis Massif by Chiara Boschi and others; a detachment system illustrates the methods without proving identical flow at every transform fault.