20. Question: How could the plates have accelerated to CPT velocities without ripping apart and without being impeded by drag from the underlying asthenosphere?
Response: As I have mentioned previously in answers to earlier questions, the fact that mantle rock weakens so dramatically with increasing temperature means that the hot asthenosphere is a thousand times, or more, weaker than most lithosphere. The presence of water at levels of 100 ppm or so within the lattices of asthenospheric minerals is likely a cause for even greater asthenospheric weakness. This is true for the earth today—even without the runaway stress weakening that kicked in to allow CPT to take place during the Flood. Here I am using weakness synonymously with low viscosity. This huge contrast in strength between lithosphere and asthenosphere means that drag forces on the base of the lithosphere tend to be negligible compared to plate strength. This contrast tends to persist as runaway rapidly reduces rock strength everywhere throughout the mantle. This contrast allows in today’s earth, for example, for the Pacific Plate to move in a highly coherent plate-like fashion—that is, with essentially no deformation internal to the plate—over a distance of more than 10,000 km (6000 mi). This represents the distance from where the Pacific Plate is forming via seafloor spreading at the East Pacific Rise—not that far west of the South American coast—to where it plunges into the Kurile-Japan-Izu-Bonin-Marianas trench in the western Pacific—roughly a quarter the distance around the earth. There is no indication of any failure in tension with regard to the huge Pacific Plate today as it moves at approximately 8 cm/yr relative to the no-net-rotation reference frame for the earth. Again, such motion is possible only because the asthenosphere is so extremely weak in comparison with the Pacific Plate, which leads to near perfect decoupling of the Pacific Plate with respect to the deep mantle except along its subducting boundary.
What about plate failure because of sudden acceleration? Even for the sorts of peak plates speeds implied by the CPT framework, which are on the order of a few meters per second, if these are realized in as little time as an hour, the acceleration implied is only a tiny fraction of one g. For example, a change in speed of 3.6 m/s spread over an hour (3600 seconds) is only 0.001 m/s2, or 0.0001 g. The level of stress associated with such small acceleration is negligible compared with the strength of a lithospheric plate.