NatGeo: Chile Earthquake (Slightly) Shortens Earth's Day

[RJN]

http://news.nationalgeographic.com/news ... tened-day/

By speeding up Earth's rotation, the magnitude 8.8 earthquake—the fifth strongest ever recorded, according to the USGS—should have shortened an Earth day by 1.26 millionths of a second, according to new computer-model calculations by geophysicist Richard Gross of NASA's Jet Propulsion Laboratory in California.

[BMAONE23]

As the temblor didn't happen at the point where the plates meet, it occured deeper along the subduction zone of the fault. Their explanation of the compressive forcing of material closer to the core creating a slightly faster spin makes sence, initially, but being in a subduction zone, wouldn't the slip also have forced the upper layer (south american plate) to raise away from the core possibly offsetting any spin rate gain from comperssion?

[neufer]

As the temblor didn't happen at the point where the plates meet, it occurred deeper along the subduction zone of the fault. Their explanation of the compressive forcing of material closer to the core creating a slightly faster spin makes sense, initially, but being in a subduction zone, wouldn't the slip also have forced the upper layer (south american plate) to raise away from the core possibly offsetting any spin rate gain from compression?

What went down was denser than what went up.