Earth tide

March 10, 2011 6:48 PM

"The Earth tide is a little-known daily event, similar to the oceans' more familiar tides. But the sun and moon's gravity doesn’t just pull on water, it deforms the Earth itself, causing the ground beneath us to bulge toward the pulling heavenly body."

[wiki]

Could it cause earthquakes? Will a supermoon kill us all? Not likely, but linear accelerators and GPS have to account for this daily shift.

posted by Paragon (12 comments total)

The Earth tide is a little-known daily event...

lolwhat
posted by DU at 6:55 PM on March 10, 2011

20-30 centimeters? Seriously? That's incredible.
posted by Xoebe at 7:36 PM on March 10, 2011

The earth tide goes in, the earth tide goes out, never a miscommunication.
posted by Huck500 at 7:43 PM on March 10, 2011 [2 favorites]

Yup, you see this in all kinds of instruments like tilt sensors, accelerometers and the like if you have frequency response in millihertz. Accounting for the tilt in calibration gear isn't rocket science but it can catch you out if you don't expect it on, for example, tilt sensors on bridges.
posted by jet_silver at 7:44 PM on March 10, 2011

Indeed it appears I was correct. It is literally incredible, and should be given no credence.

From the linear accelerator link:

"The measurements revealed several unexpected facts. One is that the observed motion has very clear daily and half-daily periods. Detailed analysis confirmed that this motion is indeed tidal -- that is, produced by gravitational attraction of the moon and sun on the Earth.

The amplitude of the observed tidal motion was surprisingly large -- about 10 microns, or a hundred times larger than expected. This anomaly is explained by SLAC's location near the Pacific Coast. When the ocean tides change the water level at the shore, this water produces additional pressure that increases the deformation of the nearby Earth. Called "ocean loading," this phenomenon has been known to geophysicists for more than 30 years."

The 10 microns is the tidal deformation amplified by ocean effects.

20-30 centimeters. Give me a fucking break.

The same first link article, I was also all "WTF" when they referred to back tracking seismic waves as "really remarkable work". Yeah - for 1750 maybe. That's A.D. Is the Harvard Gazette a satirical rag, like The Onion?
posted by Xoebe at 7:45 PM on March 10, 2011 [2 favorites]

Woops. I thought I edited out the f-bomb in there, sorry.
posted by Xoebe at 7:45 PM on March 10, 2011

Apology rejected. Forgiveness denied.

BtW, remember that the melting of the polar ice caps means geostatic rebounding, which means increased seismic activity (read: earthquakes and tsunamii (tsunamae?)). =D
posted by Eideteker at 9:38 PM on March 10, 2011

So, that wasn't me making the Earth move? She lied!
posted by brundlefly at 10:07 PM on March 10, 2011

ApoloBtW, remember that the melting of the polar ice caps means geostatic rebounding, which means increased seismic activity (read: earthquakes and tsunamii (tsunamae?)).
posted by Eideteker at 9:38 PM on March 10 [+] [!]

You posted that at 9:38PM PST, or 2:39PM in Japan, about 7 minutes before the 8.9 magnitude earthquake hit Japan, followed by a tsunami.
posted by eye of newt at 11:43 PM on March 10, 2011

Ugh. I really wish I hadn't made that joke now.
posted by brundlefly at 12:08 AM on March 11, 2011 [2 favorites]

No, the “supermoon” didn’t cause the Japanese earthquake
posted by 1970s Antihero at 11:35 AM on March 11, 2011

There really ARE earth tides, as one who has spent some time reading gravity meters on gravity surveys (yes, there are such things), I can tell you that if a fault is Just... about ready to break, the tidal force could be just the camels last straw, so to speak.
posted by primdehuit at 10:40 AM on March 12, 2011 [1 favorite]