WEBVTT - BrainStuff Classics: Does Earth's Crust Have Its Own Tides?

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<v Speaker 1>Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff,

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<v Speaker 1>Lauren Vogel bomb here with a classic episode from the archives.

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<v Speaker 1>Tides are fascinating phenomena, and the Earth's oceans aren't the

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<v Speaker 1>only places where they're found. It turns out that the

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<v Speaker 1>Earth's crust itself is subject to tides. Hey brain Stuff,

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<v Speaker 1>Lauren Vogel bomb here. If you earn your living on

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<v Speaker 1>the ocean, you'd better know how to read a tide table.

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<v Speaker 1>Around the world, most coastal communities witness sea levels rise

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<v Speaker 1>and fall multiple times every day. The effect can be

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<v Speaker 1>quite dramatic. On certain days, there's a fifty three ft

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<v Speaker 1>that's sixteen meter difference between the low and high tides

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<v Speaker 1>in Canada's Immunis Basin Inlet. For example, working fishermen, divers,

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<v Speaker 1>and ship captains must take fluctuations like these into account.

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<v Speaker 1>For this reason, government's released tables that predict the heights

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<v Speaker 1>of future tides four different corners of the oceans. Yet,

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<v Speaker 1>unbeknownst to us, the ground beneath our feet experiences tides

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<v Speaker 1>of its own. The phenomenon goes by many names, including

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<v Speaker 1>land tides, crustal tides, earth tides, and more. Specifically solid

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<v Speaker 1>Earth tides. No matter what you call the process, it's

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<v Speaker 1>caused by the same forces that generate our better known

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<v Speaker 1>oceanic tides. Tides are complicated beasts. They are the result

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<v Speaker 1>of several different factors all working together. The most significant

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<v Speaker 1>contributing forces are the gravitational pulls that the Sun, Moon,

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<v Speaker 1>and the Earth exert on one another. The Sun actually

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<v Speaker 1>has less influence over our tides than the Moon does,

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<v Speaker 1>despite being twenty two million times larger. That's because the

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<v Speaker 1>Moon is so much closer to Planet Earth. As such,

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<v Speaker 1>on the surface of Earth, the Moon's gravitational force is

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<v Speaker 1>about two point two times stronger than the Sun's. High

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<v Speaker 1>ocean tides, at least in most parts of the world,

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<v Speaker 1>happened twice a day. We experience one when the Moon

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<v Speaker 1>is overhead, and, counterintuitive as it may sound, a second

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<v Speaker 1>tide tide takes place when the Moon is on the

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<v Speaker 1>opposite side of Earth. Low ocean tides occurred during the

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<v Speaker 1>periods between these two points. The centrifugal force of our

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<v Speaker 1>rotating planet helps account for this strange bulging effect. While

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<v Speaker 1>this is happening, a similar cycle unfolds within the very

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<v Speaker 1>crust of our planet to a minuscule degree. The ground

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<v Speaker 1>level itself rises and falls every day in accordance with

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<v Speaker 1>the moon's whereabouts. We spoke with Duncan Agnew, a geophysicist

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<v Speaker 1>at Scripps Institution of Oceanography at the University of California,

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<v Speaker 1>San Diego. He said the motion extends through the whole

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<v Speaker 1>of the solid Earth, not just the crust, but is

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<v Speaker 1>largest at the surface. The earth is slightly elastic. Your

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<v Speaker 1>naked eyes all that's required to watch the ocean tide

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<v Speaker 1>come in and go out. However, it's straight up impossible

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<v Speaker 1>to observe solid earth tides without using scientific instruments. At

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<v Speaker 1>high tide, New York City can rise upward by fourteen

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<v Speaker 1>inches that's about thirty six centimes. The Big Apple then

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<v Speaker 1>falls by the same degree at low tide. A pedestrian

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<v Speaker 1>standing in Times Square or the Bronx wouldn't notice any

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<v Speaker 1>of this, though, because all of the buildings, trees, streets,

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<v Speaker 1>and people in the Five Burrows rise and fall in concert.

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<v Speaker 1>Though that's just one example. Acnew says that the vertical

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<v Speaker 1>motion at the surface varies from place to place. Some

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<v Speaker 1>areas bulge and descend less dramatically than New York does

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<v Speaker 1>other locales outperformed the Big City on that score. Okay,

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<v Speaker 1>so far we focused on how the Moon affects both

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<v Speaker 1>solid Earth and oceanic tides, but the Sun should not

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<v Speaker 1>be ignored in this discussion. Those who live in coastal

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<v Speaker 1>areas are well aware of how solar activity can affect

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<v Speaker 1>the strength of oceanic tides. When the Sun aligns with

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<v Speaker 1>the Moon, the seas high tides get higher and the

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<v Speaker 1>low tides get lower. The exact opposite happens when those

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<v Speaker 1>two celestial bodies are situated at right angles to one another,

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<v Speaker 1>meaning the planet ends up with low high tides and

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<v Speaker 1>high low tides. That cycle repeats itself every two weeks

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<v Speaker 1>and is therefore known as the Fortnightly cycle. On top

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<v Speaker 1>of giving voters headaches, it also affects sol at earth tides.

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<v Speaker 1>Nicholas vander Elst of the U S Geological Survey was

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<v Speaker 1>the lead author of a sixteen study that investigated the

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<v Speaker 1>link between the Fortnite cycle, land tides, and seismic activity

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<v Speaker 1>along California's San Andreas Fault. He said via email, when

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<v Speaker 1>the Earth's crust flexes in the direction of the title pull,

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<v Speaker 1>this puts a stress on any tectonic faults that cut

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<v Speaker 1>through the rock. If the combination of the title stress

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<v Speaker 1>and the pre existing tectonic stress is just right, this

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<v Speaker 1>can set off an earthquake. For that steen research effort,

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<v Speaker 1>vander Elsts group compared eighty one thousand San Andreas earthquakes.

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<v Speaker 1>They found that the rate of low frequency quakes increases

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<v Speaker 1>right before the fortnightly cycle enters its solar lunar alignment stage.

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<v Speaker 1>But Californians shouldn't lose too much sleep over this news development.

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<v Speaker 1>The earthquakes in question are too weak and occur too

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<v Speaker 1>far below the planet's surface to cause any serious damage

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<v Speaker 1>on the surface. Crystal tides vander Eilst notes are generally

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<v Speaker 1>quote far too small to matter for most faults. Nonetheless,

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<v Speaker 1>the geologist has found that it's possible to observe a

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<v Speaker 1>small but measurable influence in some locations, particularly in places

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<v Speaker 1>like mid ocean ridges. There are also special regions of

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<v Speaker 1>the Earth's crust where fault lines appear to be astoundingly weak.

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<v Speaker 1>These regions tend to be deep at the roots of

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<v Speaker 1>subduction zone faults, like the faults that dive beneath Japan

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<v Speaker 1>and the U. S Pacific northwest. Down there, some twelve

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<v Speaker 1>to eighteen miles or twenty to thirty kilometers beneath the

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<v Speaker 1>planet's surface, faults create small scale seismic tremors. Van Dryilst

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<v Speaker 1>said the tides can have a very substantial effect on tremors,

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<v Speaker 1>with tremor rates oscillating by up to thirty percent in

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<v Speaker 1>phase with the tides. However, these tiny pseudo earthquakes are

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<v Speaker 1>totally undetectable by people and do not pose any hazard. Still,

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<v Speaker 1>it's pretty fascinating. Oh and hey, the ocean is not

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<v Speaker 1>the only body of water that experiences its own tides.

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<v Speaker 1>Lakes undergo them as well, but on a much smaller scale.

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<v Speaker 1>For example, the mightiest tides on North America's Great Lakes

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<v Speaker 1>are only five centimeters that's zero point four inches in height.

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<v Speaker 1>Today's episode is based on the article Rising Rock Earth's

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<v Speaker 1>press has its own tides too, on house touff Works

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<v Speaker 1>dot com. Written by Mark Mancini. Brain Stuff is production

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<v Speaker 1>by Heart Radio in partnership with house Toffworks dot Com,

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<v Speaker 1>and it's produced by Tyler Clay. Before more podcasts my

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<v Speaker 1>heart Radio, visit the i Heart Radio app, Apple Podcasts,

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