# Tag: earthquakes

## What's with all these earthquakes?

By Phil Plait | August 25, 2011 6:27 am

The Earth is trembling.

A magnitude 5.9 earthquake hit Virginia on August 23 at 17:51 UTC. Twelve hours earlier, a magnitude 5.3 quake shook southern Colorado (I slept through it; it was 360 km away). On August 20, a magnitude 7.0 hit off the coast of eastern Australia, and another magnitude 7.0 earthquake took place in northern Peru on August 24 at 17:46 UTC, just a few hours ago as I write this.

What gives? Are we seeing a swarm of related events? Is the Earth shaking itself apart?

It’s easy enough to think so. But our brains are wired in a way that makes them easily fooled (proof). What we need to do is not panic — always a good start — and think this through. Happily, we have an exceptionally good tool for this sort of problem: science. Well, science and a tiny touch of math.

Get me some stats, stat!

You need to look at the statistics, and not by coincidence the United States Geological Survey provides them. When you look at the chart, you see that there is 1 quake per year somewhere on Earth that’s magnitude 8 or more. There are 15 between 7.0 and 7.9 every year, or on average about one every three weeks. Mag 6? 134 per year, or 2-3 per week. Mag 5: 1300 per year, or about 4 per day.

Right away, you can see that there are going to be decent-sized earthquakes somewhere on Earth all the time. And while on average you get mag 7 quake every few weeks, in reality the distribution is random. Getting two of them within a few days of each other is not only not surprising, statistically speaking it’s expected!

It’s unusual to get a quake centered in Virginia, but it’s not that odd. They’re rare for sure, but there was a bigger one in 1897. Colorado has had its share, too. Every state in the union has quakes; I remember one in Michigan when I was an undergrad at Ann Arbor. So in and of itself, having an earthquake anywhere in the US is not necessarily suspicious. Again, a chart on that USGS page shows that we should expect 50-70 mag 5 quakes a year in the U.S., so having two even on the same day is not all that unusual.

It came from outer space

So right away, the math is telling us that these quakes are probably not really clustered, and it’s a simple coincidence. Still, maybe it’s better to be sure. Could there be some other, unearthly cause?

## Kryptonite for the supermoon

By Phil Plait | March 18, 2011 12:01 pm

[NOTE (added March 19): It occurs to me that some people might see the Moon rising today and think it looks HUGE because it’s a "supermoon". However, it’s far more likely they’re falling victim to the famous Moon Illusion. You can read all about it here.]

If you believe the mainstream media, you might think this weekend’s "supermoon" will cause earthquakes, volcanoes, bad weather, halitosis, dust bunnies, and hangnails.

Guess what I think of this idea! Hint: check the name of my blog. Got it? Good.

In reality, this "supermoon" nonsense is, well, nonsense. I have some details below, but for those of you who are impatient (the tl;dr crowd) here are the bullet points:

• Yes, the Moon is closer today than usual, but only by less than 2%.
• This does happen around full Moon, which is when we get bigger tides, but that happens every single month. The Moon being closer amplifies that, but only a tiny little bit.
• The Moon’s possible effect on earthquakes has been studied for a long time. The result? Major earthquakes are not correlated with the Moon’s position or distance.
• Therefore,

• Anyone claiming this "supermoon" can cause earthquakes or whatnot is, to be blunt, totally, completely, utterly, wrong.

Say.

OK, so, how about some details?

## No, the "supermoon" didn't cause the Japanese earthquake

By Phil Plait | March 11, 2011 10:02 am

[UPDATE: I have posted an article with more info on the earthquake and where you can donate money toward the relief efforts.]

Japan suffered a massive earthquake last night, measuring nearly magnitude 9. This is one of the largest quakes in its history, causing widespread and severe damage. Before I say anything else, I’m greatly saddened by the loss of life in Japan, and I’ll be donating to disaster relief organizations to help them get in there and do what they can to give aid to those in need.

While there isn’t much I can do to directly help the situation in Japan, I do hope I can help mitigate the panic and worry that can happen due to people blaming this earthquake on the so-called "supermoon" — a date when the Moon is especially close to the Earth at the same time it’s full. So let me be extremely clear:

Despite what a lot of people are saying, there is no way this earthquake was caused by the Moon.

The idea of the Moon affecting us on Earth isn’t total nonsense, but it cannot be behind this earthquake, and almost certainly won’t have any actual, measurable effect on us on March 19, when the full Moon is at its closest.

So, how can I be so sure?

The gravity of the situation

Here’s the deal. The Moon orbits the Earth in an ellipse, so sometimes it’s closer to us and sometimes farther away. At perigee (closest point) it can be as close as 354,000 km (220,000 miles). At apogee, it can be as far as 410,000 km (254,000 miles). Since the Moon orbits the Earth every month or so, it goes between these two extremes every two weeks. So if, say, it’s at apogee on the first of the month, it’ll be at perigee in the middle of the month, two weeks later.

The strength of gravity depends on distance, so the gravitational effects of the Moon on the Earth are strongest at perigee.

However, the Moon is nowhere near perigee right now!

The Moon was at apogee on March 6, and will be at perigee on March 19. When the earthquake in Japan hit last night, the Moon was about 400,000 km (240,000 miles) away. So not only was it not at its closest point, it was actually farther away than it usually is on average.

So again, this earthquake in Japan had nothing to do with the Moon.

Time and tide

So why would people think this is due to the Moon?

CATEGORIZED UNDER: Antiscience, Astronomy, Debunking

## Do rainbow clouds foretell earthquakes?

By Phil Plait | May 15, 2010 11:26 am

My friend Deric Hughes tipped me off to a new urban legend spreading around: rainbow clouds appearing in the sky shortly before earthquakes. Lots of folks are buzzing over this on Twitter, for example.

I’ll cut to the chase: these clouds are not physically related to earthquakes in any way. But how I know this will take a wee bit of explanation.

First, what’s a rainbow cloud? As you can see in the picture, it’s a cloud with the colors of the rainbow splashed across it. Sometimes these are called fire clouds, if the shape of the cloud resembles a fire (like in the picture above).

Second, what causes this effect? It’s pretty simple, actually. Ice crystals in the cloud act as little prisms, breaking up the sunlight into its component colors and spreading them out. It’s essentially the same thing that causes "real" rainbows, except with ice and not water droplets. The angle between the Sun, the cloud, and you is important as well, but the essential ingredients needed for this effect are icy clouds and sunlight. That’s it.

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