Having continents slide smoothly away from a central explosion does appear to produce the shapes and features of most of Earth's crust in a simple, straightforward way.  But is it physically possible for landmasses to slide?

For perspective, note that while several thousand miles is a long way for us humans, most of the continents slid only 12-16% of the distance around the world at the equator.  Australia went farthest: 23% of Earth's circumference.

People are too small to experiment with huge continents, so any explanation must be speculation.  However, there is an interesting possibility.

An odd phenomenon has been identified on Earth and other members of the solar system.  Large landslides don't just fall to the base of the mountain the way small ones do; they often go great distances, some up to 30 times the distance they fell.

Dr. H. J. Melosh has proposed that long-runnout landslides, earthquake slip, and the making of complex craters reveal a characteristic of the crust.  Put simply, it temporarily acts like a fluid when enough stress is applied.

 Well known on a small scale as a Bingham Fluid, Melosh suggests that fluidization at the base of large landslides reduces friction to near zero.  He calls it acoustic fluidization.
Acoustic Fluidization and the Extaordinary Mobility of Sturzstroms. Gareth S. Collins, H. Jay Melosh. 2003. Journal of Geophysical Research, Vol. 108, No. B10, 2473 EPM 4, pp. 1-14.
Impact Cratering: A Geologic Process. H.J. Melosh, 1989. Oxford University Press, New York.
Acoustic Fluidization: A New Geologic Process? H. Jay Melosh. Dec 10, 1979. Journal of Geophysical Research, Vol. 84, No. B13, pp. 7513-7520.

Corresponding to the fall that powers a landslide, the explosive power released by the giant meteorite on impact would have set the landmasses in motion with the force of billions of megatons of TNT, generating acoustic energy. The continental crust's mass would confine the acoustic energy to where the continental and oceanic crust meet.

The Shock Dynamics scenario

In this side view (not to scale), continental crust (brown) is on
basaltic crust and lithosphere (ochre) above the mantle (red).

The giant meteorite explodes, penetrating the continental crust.

 The force pushes up low mountains, and the landmass slides away like a ship
on water, fluidizing the contact layer.  Behind the landmass, a surface layer of
oceanic crust is melting and cooling to form the mid-ocean spreading ridge
with transform faults, pulled open by the landmass.

When the leading edge loses enough energy, the contact layer at the leading edge
solidifies.  The momentum of the landmass carries it forward like a car hitting a wall,
piling up high mountains.  The formerly fluidized contact layer in front (gray line) is a
Benioff zone, called subduction zones in Plate Tectonics.

With all the action at the surface, it follows that features in the oceanic crust are fairly shallow.  They include these:

Mid-ocean ridges and transform faults, where surface melting results from the removal of the weight of continental crust (pressure relief melting).

Trenches (green line) along the leading edges of landmasses result from the rapid application of the weight of continental crust.  Towards the end of a continent's run, friction compresses the leading edge, raising mountains.

A crustal wave (red line) from the low angle impact was launched in the direction of travel of the meteorite, and "froze" in the end to form an inclined trench.

 
Wave diffraction

Plates

The lithosphere of the earth is roughly 100 km thick.  It is divided in places, notably mid-ocean ridges and trenches.  Plate Tectonics theory is based on the notion that the lithosphere is formed at mid-ocean ridges and dives into the earth at trenches.  This is not the case in the Shock Dynamics theory, which says that the divisions in the lithosphere are features that formed at the surface and extend deep into the lithosphere, enhanced by "slow motion" differential rotation (see below).

With GPS, geologists are finding an increasing number of tiny "plates" called microplates or rigid blocks.  "With these subdivisions, the meaning of the word 'plate' as an individual mechanical entity for which we can apply concepts such as torque balance becomes less clear.  In the classical view, the motion of a plate was driven from within by body forces".  "However, a common hypothesis is that microplates are externally driven, i.e., that larger neighbor plates determine their motion."  A study of the Baja California microplate indicates that it is loosely coupled to North America, and that 90% of its motion is from being dragged by the Pacific plate.
Plattner, C., R. Malservisi, R. Govers. April 2009. On the plate boundary forces that drive and resist Baja California motion. Geology, Vol. 37, No. 4, pp. 359-362.

In the Shock Dynamics view, this kind of jostling is what is occurring today all over the globe on every "plate" in slow motion.

Slow Motion

If the work attributed to Plate Tectonics over 200 million years was actually accomplished by the Shock Dynamics event in 26 hours, what causes the few centimeters per year of motion of the "plates" measured by GPS?  The answer may be an old idea that is finding new support.

"In the hotspot reference frame a 'westward' rotation of the lithosphere can be observed.  The origin of this net rotation of the lithosphere is still under debate, but it should range between 4.9 cm/yr and 13.4 cm/yr at its equator.  This implies that... subduction zones follow or oppose the relative 'eastward' mantle flow."  "The W-directed slabs are generally very steep (up to 90°) and deep, apart a few cases such as Japan."  "The E- or NE-directed subduction zones are less inclined (15-70°), and the seismicity generally dies at about 300 km, apart from some deeper clusters close to the upper-lower mantle transition."²  In the differential rotation model, the lithosphere and outer core show a net westward drift, while the mantle and inner core move eastwards.¹

"Because the Antarctic plate is centered on the Earth's south pole and is nearly surrounded by ocean ridges, it can be regarded as an inertial reference with regard to Earth's rotation axis."³  Where the crust is thickest, such as under mountain ranges, there is the most contact with the eastward moving mantle.³

Some researchers find that the axis of rotation of the lithosphere relative to the mantle is different than the rotational axis of the whole Earth:

Global lithospheric net rotation relative to the mantle assuming a
mid-asthenospheric source of the Pacific plumes.²

Transferring the rotational path in the above illustration to a globe yields the red ring below.  For reference, the blue ring follows the equator.  The orange button at the top marks true north; the purple button marks present-day magnetic north; and the red pegs mark the axis of the red ring.

When differential rotation was proposed as a driving mechanism in the early years of Plate Tectonic theory, opponents "discarded Earth's rotation as the cause of the westward drift, claiming that the viscosity necessary to allow decoupling between lithosphere and mantle... is too low when compared with present-day estimates of the asthenosphere viscosity."³  "Tidal torque provides a sufficiently energetic mechanism to drive this motion, but requires a mechanical decoupling between the lithosphere and the deeper mantle that is incompatible with current understanding of upper-mantle viscosity."³  However, "the mantle very likely has a nonlinear rheology, and the viscosity of the asthenosphere can be far lower in thin, undetected layers."  "A thin, low-viscosity layer (shear zone) could accommodate this motion."³

"The fact that plate velocity on Earth does not depend on plate size and that the velocities of the fast plates do not depend on length of the subduction boundary suggests that it is the system, not the individual plate, that dictates plate motions."  "The possibility that has been overlooked is that the plates define and organize themselves by mutual interactions of the whole plate system and that minimization of dissipation in the lithosphere may be the organizing rule."¹

In the Shock Dynamics view, the "frozen" edges of crustal waves in the Pacific and beneath the leading edges of continents that moved became what Plate Tectonics calls plate boundaries.  They are zones of weakness in the lithosphere, subject to shear, compression or extension.  These angled faults solve the problem of subduction initiation that plagues Plate Tectonics.  Known as Benioff zones, they vary in depth up to 300 km, and apparently engage the upper mantle in its relative eastward motion, as do other deep sections of the lithosphere.  Thus the tiny measured motions of the "plates" is the interaction of certain regions of the lithosphere with the mantle as the lithosphere drifts westward.

1. Anderson, Don L. 2002. Plate Tectonics as a Far- From- Equilibrium Self-Organized System. in Plate Boundary Zones, Geodynamics Series 30, American Geophysical Union, pp. 411-425.

2. Doglioni, Carlo, Eugenio Carminati, Marco Cuffaro, Davide Scrocca. 2007. Subduction kinematics and dynamic constraints. Earth-Science Reviews, Vol. 83, pp. 125-175.

3. Scoppola, B., D. Boccaletti, M. Bevis, E. Carminati, C. Doglioni. January/February 2006. The westward drift of the lithosphere: A rotational drag? GSA Bulletin, Vol. 118, No. 1/2, pp. 199-209.

4. Smith, Alan D., Charles Lewis. 1999. Differential rotation of lithosphere and mantle and the driving forces of plate tectonics. Geodynamics, Vol. 28, pp. 97-116.

5. Smith, Alan D., Charles Lewis. 1999. The planet beyond the plume hypothesis. Earth-Science Reviews, Vol. 48, pp. 135-182.