Saturday, January 31, 2009

Can you sing "plate tectonics"?

I mentioned the song Volcano, by the Presidents of the United States of America. Clearly they were affected by their post-Mount St. Helens days in Seattle. I heard one other rock song recently that contained the lyric "plate tectonics," I'll have to go back and find it. Do you know of any? Yes, I know there is probably some group playing in Santa Cruz named the Be Good Tanya Atwaters, but I'm thinking more mainstream here.

The Presidents sing Volcano live on the Jenny McCarthy show (take what she says about autism with many grains of salt):

Or go watch the embedding-protected studio version. I like the white lab coats, which all of us scientists wear. I wonder what the spectrum of those waves is like?

Now this is what I call rock music!

Under the island... middle of a mountain
There is a big bad... boomin' system
Blowin' speakers... woofers and tweeters
Amplifiers... melted wires
The parties exploded... the core is corroded
Under ground... the Puget Sound
Cause a shiftin'... and a driftin'
Big black boom box...stuck in the hot rock
It's in there flowin'... it's in there growin'
You don't believe me... that this scenery
Could be a cold blooded killer

It's gonna blow... Volcano
It's gonna blow... Volcano
It's gonna blow... Volcano

Now the island is shiftin'... the plates are liftin'
The core is creamy...docile and dreamy
Stopped up and steamy
Happy campers... poop in there pampers
When the mountain... becomes a fountain
Of white hot lava... molten magma
Super sonic... plate tectonics
Sterophonic... lava and tonic
The boom is bionic
Sony shut down... magnavox meltdown
Ballistic breakdown
Hi-fi heatwave... lo-fi lava cave
That sulfur smells... Mt St Helens
Pompeii was yellin'...

It's gonna blow... Volcano
It's gonna blow... Volcano
It's gonna blow... Volcano
It's gonna blow... Volcano

Friday, January 30, 2009

Has it blown yet?

Redoubt Volcano seismograph locations:

Click on above for larger version
from Alaskan Volcanological Observatory

The current seismogram at AVO can be seen here. Notice all the activity, the fairly constant amplitude, and the high frequency signals.

If you live in Anchorage, better buy your goggles and dust mask!

"It's gonna blow... Volcano"

(Lyrics from the pop song Volcano, by Presidents of the United States of America)

I only have time for a short entry, but it looks like Mt. Redoubt in Alaska may erupt. One of the omens is the occurrence of harmonic tremors that accompany movement of magma through a volcano. Volcano seismicity is physically different from the tectonic earthquakes that we usually talk about.

Check out the situation at the Alaska Volcano Observatory.

Photo: Redoubt Volcano from the AVO observation hut. The dark flow was growing while work was performed on the Redoubt webcam. Taken 27 Jan., 2009. (

Tuesday, January 27, 2009

Theme cartoon for Shaking Earth?

I need a break from that Lancaster earthquake!

Maybe I need ... humor?

This site seems pretty funny, but that could just be me.

Saturday, January 24, 2009

Will Obama = better science?

I wonder if seismographs could detect the huge crowds in Washington, DC, last Tuesday?

I don't want to get too political here, but I can't help but think the change in administration is a good thing for science. It's a sad day (or eight years) when science policy (not to mention other policies) are driven by a desired goal, and not by the evidence.

Many scientists seem to agree, according to the International Herald Tribune.

And, of course, don't feed the trolls, or bad science blogs!

Lancaster earthquakes - how dense are they?

Or, after another entry on the Lancaster earthquake, you might be asking how dense is Rob?


The gray color suggests that there is about 0.1 magnitude 5 earthquakes in that region per year, or only 1 every 10 years (which actually seems a bit high to me). But in the Lancaster area, colored white, the frequency is even less. This actually isn't a very interesting diagram here because of the paucity of large earthquakes. We'll have to look at this type of diagram later for a larger earthquake, presumably in some other part of the world near a plate boundary.

Wednesday, January 21, 2009

Seismic hazard map - it's not just a west coast thing

We're still not done with that pesky little Lancaster earthquake.

Keep going down the page there, and click on Seismic Hazard Map.

The main seismic hazard in this part of the country is from ground acceleration. The map suggests that in the Lancaster area, midway between Harrisburg and Philadelphia, there is a 20% chance that a seismic ground acceleration as high as 1/5 of gravitational acceleration will occur within a 50-year period of time. Doesn't sound all that dangerous. Any thoughts from others?

In other areas, the earthquake hazard can take on other forms.

Saturday, January 17, 2009

Lancaster earthquake - just a phase?

We're still doing an extended tutorial on the Lancaster earthquake.

Go down the page there, and click on Phase (Arrival Time) Data.

This shows the phases recorded at different seismic station. We know already that there are three physically different types of seismic waves - P, S, and L. But phase not only indicates which type of wave, but what path it has traveled.

You can find a listing of seismic phases here.

Note in particular the phases for the Lancaster quake:
  • Pg - at short distances, an upgoing P wave from a source in the upper crust
  • Pn - a P wave refracted along the crust-mantle boundary
  • Sg - at short distances, an upgoing S wave from a source in the upper crust
  • Sn - an S wave refracted along the crust-mantle boundary

I think the preceding e you find for some phases indicates an "emergent" phase, one that is not too sharp, but builds up more gradually. Confirmation, anyone?

Monday, January 12, 2009

Lancaster quake - how fast do seismic waves travel?

Seismic waves travel pretty fast. There are three physically different types of waves - P, S, and L. The velocity depends on which type of wave and what part of the earth you are in - crust, mantle, core. But my rule of thumb for velocities of seismic waves that travel some distance from the epicenter is about 8 km/second (or 8000 meters/second) for a P wave, and 5 km/second for an S wave. Compare this with common velocities such as driving your car at 60 mph, which is about 100 km/hour, or 2 km/minute, or 0.03 km/second (all back of the envelope calculations).

So look at the NEIC report for the Lancaster quake. Now go to the link for Theoretical P-Wave Travel Times. The figures and table tell you how long it will take the P-waves from this quake to travel different distances. Note that these are essentially spherical wavefronts, since the waves travel out at constant velocities in all directions.

click above for larger image
Now this was a small quake, so the waves won't be large enough to be detectable more than a few hundred kilometers away, but this shows how many minutes it would theoretically take the waves to travel out to various distances: to New York in less than 1 minute, to Chicago in 2 minutes, Miami in 3 minutes, Denver in 5 minutes, and on to San Francisco in 7 minutes. There is another map on the same page for times around the world, and a table with the same information. We'll have to return to this topic at some point for a larger quake to understand the nature of the shadow zone.

Friday, January 9, 2009

Lancaster - Historic Seismicity

Ok, let's go back to the NEIC web page for the recent Lancaster earthquake.

Now click on the link down the page on Historic Seismicity.

click on above for larger image

This is a cool graphic. Previous earthquake epicenters are indicated with the circles. The radius of the circle indicates the earthquake magnitude. And the depth of the epicenter is shown by the color. So four dimensions of data are shown on a two-dimensional figure.

All of the historic quakes shown are small, and all are shallow.

Note the last line in the figure caption. Plate boundaries, that is, the type of boundary between different plates in the plate tectonics model, are indicated. In this area, there are no plate boundaries. Thus, these are examples of intraplate earhquakes, those that occur within a plate, as opposed to the interplate earthquakes that occur at boundaries between different plates.

It will be useful at a later time to compare this earthquake to one at a plate boundary, in an area of much higher seismicity.

Tuesday, January 6, 2009

How intense is that? Lancaster earthquake intensities

Notice now that the Lancaster quake NEIC report now lists it as magnitude 3.4 . Re-evaluation of the data?

An earthquake magnitude is an objective measure of the energy released. It is based on seismograph readings, and is a single number that characterizes the size of the earthquake. The first methods for determining magnitudes were derived by seismologist Charles Richter, so although different algorithms are now used, these are still often called Richter magnitudes.

Intensities are another way of indicating the nature of seismic ground motion in a particular area, and the response of people and structures to that ground motion. It is somewhat subjective; intensities vary from being highest near the epicenter, to decreasing values at greater distances. The Modified Mercalli Intensity Scale is the one in common usage today.

click above for larger image

Notice the intensities for the Lancaster quske as shown above are all Roman numerals II and III - compare these to the description above for the Modified Mercalli Scale.

Monday, January 5, 2009

Update on Dillsburg swarm

Jeri Jones, a geologist in York County, PA, has been compiling a list of all felt earthquakes reported to him by residents of the Dillsburg, PA, area. As of January 1, there are 206 earthquakes on the list! Please contact me if you want a copy of the list.

Sunday, January 4, 2009

NEIC post on Lancaster earthquake

The U.S. Geological Survey's Earthquake Hazards Program (aka National Earthquake Information Center) web pages have great information on earthquakes. Let's look at the information provided for the recent Lancaster earthquake.

First, the basics, to be found here, or copied below:

(click above for a larger image)

Obviously, this page gives the basic hypocenter or focus, epicenter, and magnitude information on the quake: where, when, how deep, how big, what cities was it close to (where damage might have occurred), and indicators of uncertainty and reliability. Meanings of the terms are given here; note the different types of magnitudes, perhaps the source for a future blog.

Friday, January 2, 2009

Good vibrations (Beach Boys style)

If we want to start the year with good vibrations, what better way than with the Beach Boys:

This 1966 song was a #1 hit for the Beach Boys, and is one of the The Rock and Roll Hall of Fame's 500 Songs that Shaped Rock and Roll.

Perhaps the Southern California Beach Boys hit was influenced by the 1966 Parkfield magnitude 6.0 earthquake earlier that summer?