[editor-surveyor]

"If an earth quake can accelerate the rotation with a certain movement or change in placement of mass, isn't it equally likely to slow the rotation with an opposing change from a different shift in tectonics?"

The assumption is that the circumference decreased slightly, thus accelerating the rotation much as a figure skater accelerates her spin by pulling her arms inward. The angular momentum must remain constant.

[downtownconservative]

True. But an earth quake could correspondingly increase diameter as well (depending on the nature of the quake), which would have the opposite affect.

[Reeses]

a figure skater accelerates her spin by pulling her arms inward.

She throws out a thigh to power up the spin but I think her arms are mostly a wind resistance problem.

Gravity and our weight are a little less now if Earth is spinning faster. Speaking of weight I wonder what Hillary's flight to the Southern Hemisphere has done to Earth's wobble.