Speaker 1: Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff,
Speaker 1: Lauren Vogel bomb here with a classic episode from the archives.
Speaker 1: Tides are fascinating phenomena, and the Earth's oceans aren't the
Speaker 1: only places where they're found. It turns out that the
Speaker 1: Earth's crust itself is subject to tides. Hey brain Stuff,
Speaker 1: Lauren Vogel bomb here. If you earn your living on
Speaker 1: the ocean, you'd better know how to read a tide table.
Speaker 1: Around the world, most coastal communities witness sea levels rise
Speaker 1: and fall multiple times every day. The effect can be
Speaker 1: quite dramatic. On certain days, there's a fifty three ft
Speaker 1: that's sixteen meter difference between the low and high tides
Speaker 1: in Canada's Immunis Basin Inlet. For example, working fishermen, divers,
Speaker 1: and ship captains must take fluctuations like these into account.
Speaker 1: For this reason, government's released tables that predict the heights
Speaker 1: of future tides four different corners of the oceans. Yet,
Speaker 1: unbeknownst to us, the ground beneath our feet experiences tides
Speaker 1: of its own. The phenomenon goes by many names, including
Speaker 1: land tides, crustal tides, earth tides, and more. Specifically solid
Speaker 1: Earth tides. No matter what you call the process, it's
Speaker 1: caused by the same forces that generate our better known
Speaker 1: oceanic tides. Tides are complicated beasts. They are the result
Speaker 1: of several different factors all working together. The most significant
Speaker 1: contributing forces are the gravitational pulls that the Sun, Moon,
Speaker 1: and the Earth exert on one another. The Sun actually
Speaker 1: has less influence over our tides than the Moon does,
Speaker 1: despite being twenty two million times larger. That's because the
Speaker 1: Moon is so much closer to Planet Earth. As such,
Speaker 1: on the surface of Earth, the Moon's gravitational force is
Speaker 1: about two point two times stronger than the Sun's. High
Speaker 1: ocean tides, at least in most parts of the world,
Speaker 1: happened twice a day. We experience one when the Moon
Speaker 1: is overhead, and, counterintuitive as it may sound, a second
Speaker 1: tide tide takes place when the Moon is on the
Speaker 1: opposite side of Earth. Low ocean tides occurred during the
Speaker 1: periods between these two points. The centrifugal force of our
Speaker 1: rotating planet helps account for this strange bulging effect. While
Speaker 1: this is happening, a similar cycle unfolds within the very
Speaker 1: crust of our planet to a minuscule degree. The ground
Speaker 1: level itself rises and falls every day in accordance with
Speaker 1: the moon's whereabouts. We spoke with Duncan Agnew, a geophysicist
Speaker 1: at Scripps Institution of Oceanography at the University of California,
Speaker 1: San Diego. He said the motion extends through the whole
Speaker 1: of the solid Earth, not just the crust, but is
Speaker 1: largest at the surface. The earth is slightly elastic. Your
Speaker 1: naked eyes all that's required to watch the ocean tide
Speaker 1: come in and go out. However, it's straight up impossible
Speaker 1: to observe solid earth tides without using scientific instruments. At
Speaker 1: high tide, New York City can rise upward by fourteen
Speaker 1: inches that's about thirty six centimes. The Big Apple then
Speaker 1: falls by the same degree at low tide. A pedestrian
Speaker 1: standing in Times Square or the Bronx wouldn't notice any
Speaker 1: of this, though, because all of the buildings, trees, streets,
Speaker 1: and people in the Five Burrows rise and fall in concert.
Speaker 1: Though that's just one example. Acnew says that the vertical
Speaker 1: motion at the surface varies from place to place. Some
Speaker 1: areas bulge and descend less dramatically than New York does
Speaker 1: other locales outperformed the Big City on that score. Okay,
Speaker 1: so far we focused on how the Moon affects both
Speaker 1: solid Earth and oceanic tides, but the Sun should not
Speaker 1: be ignored in this discussion. Those who live in coastal
Speaker 1: areas are well aware of how solar activity can affect
Speaker 1: the strength of oceanic tides. When the Sun aligns with
Speaker 1: the Moon, the seas high tides get higher and the
Speaker 1: low tides get lower. The exact opposite happens when those
Speaker 1: two celestial bodies are situated at right angles to one another,
Speaker 1: meaning the planet ends up with low high tides and
Speaker 1: high low tides. That cycle repeats itself every two weeks
Speaker 1: and is therefore known as the Fortnightly cycle. On top
Speaker 1: of giving voters headaches, it also affects sol at earth tides.
Speaker 1: Nicholas vander Elst of the U S Geological Survey was
Speaker 1: the lead author of a sixteen study that investigated the
Speaker 1: link between the Fortnite cycle, land tides, and seismic activity
Speaker 1: along California's San Andreas Fault. He said via email, when
Speaker 1: the Earth's crust flexes in the direction of the title pull,
Speaker 1: this puts a stress on any tectonic faults that cut
Speaker 1: through the rock. If the combination of the title stress
Speaker 1: and the pre existing tectonic stress is just right, this
Speaker 1: can set off an earthquake. For that steen research effort,
Speaker 1: vander Elsts group compared eighty one thousand San Andreas earthquakes.
Speaker 1: They found that the rate of low frequency quakes increases
Speaker 1: right before the fortnightly cycle enters its solar lunar alignment stage.
Speaker 1: But Californians shouldn't lose too much sleep over this news development.
Speaker 1: The earthquakes in question are too weak and occur too
Speaker 1: far below the planet's surface to cause any serious damage
Speaker 1: on the surface. Crystal tides vander Eilst notes are generally
Speaker 1: quote far too small to matter for most faults. Nonetheless,
Speaker 1: the geologist has found that it's possible to observe a
Speaker 1: small but measurable influence in some locations, particularly in places
Speaker 1: like mid ocean ridges. There are also special regions of
Speaker 1: the Earth's crust where fault lines appear to be astoundingly weak.
Speaker 1: These regions tend to be deep at the roots of
Speaker 1: subduction zone faults, like the faults that dive beneath Japan
Speaker 1: and the U. S Pacific northwest. Down there, some twelve
Speaker 1: to eighteen miles or twenty to thirty kilometers beneath the
Speaker 1: planet's surface, faults create small scale seismic tremors. Van Dryilst
Speaker 1: said the tides can have a very substantial effect on tremors,
Speaker 1: with tremor rates oscillating by up to thirty percent in
Speaker 1: phase with the tides. However, these tiny pseudo earthquakes are
Speaker 1: totally undetectable by people and do not pose any hazard. Still,
Speaker 1: it's pretty fascinating. Oh and hey, the ocean is not
Speaker 1: the only body of water that experiences its own tides.
Speaker 1: Lakes undergo them as well, but on a much smaller scale.
Speaker 1: For example, the mightiest tides on North America's Great Lakes
Speaker 1: are only five centimeters that's zero point four inches in height.
Speaker 1: Today's episode is based on the article Rising Rock Earth's
Speaker 1: press has its own tides too, on house touff Works
Speaker 1: dot com. Written by Mark Mancini. Brain Stuff is production
Speaker 1: by Heart Radio in partnership with house Toffworks dot Com,
Speaker 1: and it's produced by Tyler Clay. Before more podcasts my
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