Scientists at the U.S. Geologic Survey (USGS) pinpointed the source of the tremors that were felt across the Midwest last Friday.

“The April 18 earthquake is located within the Illinois basin-Ozark dome region, which covers parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas and stretches from Indianapolis and St. Louis to Memphis. Moderately damaging earthquakes have historically occurred at irregular intervals in this region, ….,” according to the USGS National Earthquake Information Center.

The location of the 18 April 2008 earthquake felt across the Midwest. Map courtesy the USGS.

The earthquake experts place the quake seven miles below a point on earth’s surface near the small town of Bellmont, IL. A tremendous amount of information about this event is available online at http://earthquake.usgs.gov.

Just three days after the quake, the USGS released an updated national seismic hazard map. This map shows that earthquakes may occur just about anywhere in the U.S. (and around the world), but fortunately for us here in West MI, a significant shaker is highly unlikely to strike close to home.

2008 update of the US seismic hazard map produced by the USGS.

Data that scientists use to pinpoint earthquakes and estimate their hazards come from sensitive vibration-measuring instruments called seismometers. If data recorded by a seismometer during an earthquake is played back fast (like playing a 33 at 45 — OK, only some of know what that means) they sound like sounds. Click this sentence for a sample.

More samples of earth’s seismic sounds are available at http://earthquake.usgs.gov/learning/listen/.

Earth is a dense, rocky place that crunches and grinds as it ages and settles. The sounds it makes are much like you might imagine, sort of crunchy and grindy — not really music to anyone’s ears.

But another solar system body sings in much more beautiful notes: the sun. Because the sun is not solid it vibrates and rings much more freely than does earth.

Scientists study the sun in extraordinary detail. One of the main instruments used to study the sun is the Solar and Heliospheric Observatory, or SOHO for short. SOHO is a satellite built and managed by a host of universities and research centers around the world, including NASA and the European Space Agency. One of the things that SOHO observes about the sun is the way it vibrates.

“The outermost quarter of the Sun’s interior is a constantly churning maelstrom of hot gas. Turbulence in this region causes ripples that criss-cross the solar surface, making it heave up and down in a patchwork pattern of peaks and troughs,” according to a recent mission summary on the SOHO website http://sohowww.nascom.nasa.gov.

A computer-generated representation of the vibrating sun from an introduction to helioseismology at http://soi.stanford.edu/results/heliowhat.html.

An MPEG video clip of ripples on the seething surface of the sun is available at http://soi.stanford.edu/press/agu05-98/flare.mpg.

SOHO measures the sun’s vibrations with a device called the MDI (short for something much longer), which is something like a solar seismometer. The MDI is a project of the Stanford-Lockheed Institute for Space Research. Like earthquake data, if MDI data are sped up and played back, they also sound like sounds. Click this sentence for a sample.

More sun sounds are available at http://solar-center.stanford.edu/singing/.

The sounds of the sun are sometimes peaceful and pleasant, like a meditation gong, yet sometimes a bit rough. The rough sounds are those of sunquakes — powerful waves that ripple around the sun from time to time — caused by solar flares.

So there are earthquakes on earth and sunquakes on the sun. Because things are better in threes I’ll note that seismometers left on the moon by the Apollo astronauts confirmed that there are also moonquakes on the moon.

Buzz Aldrin (Apollo 11) deploys a seismometer in the Sea of Tranquillity. Image courtesy NASA.

Look for a new post on or about 4 May 2008.