The 2004 Indonesian and 2010 Chilean Earthquakes and Earth’s Rotation
Since the great 2004 Indonesian earthquake I have gotten numerous inquiries about whether the earthquake affected the earth’s axis.
What was affected was the so-called Chandler Wobble. Objects that are not perfectly spherical do not rotate around a single axis. That’s just the laws of physics. I did the math in graduate school. Unless you know tensors, you don’t want to go there. Anyway, the earth doesn’t rotate smoothly around its axis, instead, the poles wander in rough circles about 10 meters in diameter. Another way to say it is your latitude changes a bit (0.7 seconds of arc) over a cycle of about a year. Anything that redistributes mass on the earth, even weather systems and the circulation of the oceans, can affect this wobble detectably. Think of a bunch of people on a merry-go-round all running over to one side. Since we can routinely locate ourselves nowadays to accuracies of meters, and precise surveys can locate points to millimeters, we can detect even these tiny changes. What happened here was a big chunk of the northern Indian Ocean lurched northward 10-20 meters relative to Asia. It also descended several meters into the mantle, and compressed and elevated northern Sumatra by several meters. It also likely triggered big submarine landslides that caused the tsunamis. So a fair amount of mass got redistributed. The U.S. Naval Observatory tracks this stuff and will tell you all you want to know about it, but I haven’t see anything posted about the big quake yet. However, the US Geological Survey posted this:…
change in length of day: -2.676 microseconds
polar motion excitation X : -0.670 milliarcseconds
polar motion excitation Y: 0.475 milliarcseconds….<!–more–>
Japan Earthquake Shortened Days, Increased Earth’s Wobble
The magnitude 9.0 earthquake that struck Japan last Friday was powerful enough to shorten Earth’s day by 1.8 microseconds and throw an extra 6.7 inches (17 centimeters) into the planet’s wobble, scientists say.
That doesn’t mean shockwaves from the event somehow knocked Earth off its north-south axis, around which the planet revolves.
Instead the quake shifted what’s called Earth’s figure axis, an imaginary line around which the world’s mass is balanced, about 33 feet (10 meters) from the north-south axis.
Earth naturally wobbles slightly as it spins, because shifting surface mass such as melting glaciers and moving ocean currents can throw the planet off balance.
Data from high-precision GPS instruments show that parts of Japan shifted by as much as 13 feet (4 meters) as the fault plates lurched due to the earthquake. This allowed scientists to calculate how much Earth’s overall mass distribution had shifted and thus how much the wobble was affected…. <!–more–>
Quake moved Japan coast 8 feet, shifted Earth’s axis
(CNN) — The powerful earthquake that unleashed a devastating tsunami Friday appears to have moved the main island of Japan by 8 feet (2.4 meters) and shifted the Earth on its axis.
“At this point, we know that one GPS station moved (8 feet), and we have seen a map from GSI (Geospatial Information Authority) in Japan showing the pattern of shift over a large area is consistent with about that much shift of the land mass,” said Kenneth Hudnut, a geophysicist with the U.S. Geological Survey (USGS).
Reports from the National Institute of Geophysics and Volcanology in Italy estimated the 8.9-magnitude quake shifted the planet on its axis by nearly 4 inches (10 centimeters)…. <!–more–>