Saturday, April 23, 2011

Michael Welland on the geoblogosphere

I came across this commentary from May of 2010 on the value of the "geoblogosphere." I thought I would pass it along, even though I didn't make Welland's list of blogs he reads. But he did lead to to a master list of geo blogs, and at least we're on that!

He is a recent convert to blog reading. He says:
.... but what’s the point? Why do these geologists write blogs and what is their value? A recent survey of the geoblogosphere conducted by Lutz Geissler of the Technical University Bergakademie in Freiberg, in collaboration with Robert Huber of the University of Bremen and Callan Bentley of Northern Virginia Community College, helps answer the first question and informs the second. The equally top-ranked responses to the question “why do you blog?” were “to inform”, “to share knowledge”, and “to popularise the geosciences” (followed closely by “to have fun”).

Combine this motivation and energy with the significant audience for many of these blogs, and there is arguably the prime value: knowledge-sharing and outreach...

What the majority have in common, however, is that they are current and immediate. Whether reporting on an ongoing research or fieldwork project, a volcanic or seismic event, providing links to newly published papers, or seeking ideas on the design of a new course, these blogs represent a unique means of rapidly disseminating – and accessing – information and ideas.

Thursday, April 21, 2011

Listening (literally) to the Japanese earthquake

NOAA has an audio of seismic waves generated by the Toholu earthquake.  Seismic P-waves are, after all, essentially the same as sound waves.

Scientists at the NOAA Vents Program at Pacific Marine Environmental Laboratory and Oregon State University heard the March 11, 2011 Honshu, Japan earthquake using a hydrophone located near the Aleutian Islands of Alaska.

Monday, April 18, 2011

Tohoku quake and free oscillations

Large earthquake cause the Earth to "ring like a bell," the phenomenon of free oscillations.

There are nice animations of the different toroidal and spheroidal modes of free oscillations at this web page from Lucien Saviot of the CNRS.  Note the periods of the oscillations.

The image below shows the response of the superconducting gravimeter at Metsähovi, Finland.  The gravimeter is also a long period seismometer. Time runs from the day of the quake on the left to five days later on the right.  Hotter colors are higher amplitudes.  The scale on the left gives the frequency of oscillation, where f=0.0006 cycles/second corresponds to a period of oscillation of 28 minutes.

Another reprsentation of some of the free oscillation data in the lower part of the frequency spectrum is shown below, from the same source.
 The lowest mode is spheroidal mode 0S2 (54 minutes). All modes decay after a few days, except the lowest radial mode (0S0) which has an expected lifetime of 3-4 months. The radial oscillation mode changes radius of the Earth with the period of 20 minutes. The observed amplitude at Metsähovi is 0.06 mm on 17.3.2011.

Free oscillations of the Earth which had been theoretically predicted were first observed after the 1960 Chile quake, the largest earthquake ever recorded.

Sunday, April 10, 2011

Google searches, blog hits

Sometimes I wonder why and when I get hits for the blog. My colleague Teb recently showed me Google Trends, a neat tool that lets you look at trends in Google searches on one or more terms. The term "Japan earthquake brought up the following trend. The peak, of course, is when the Japanese earthquake occurred on March 11, with a decrease ever since.

Google Analytics also allows one to monitor the hist on one's own web site. Can't say I have mastered it yet (I don't find it too user friendly), but the graph below shows the hits on this blog, also since the Japan quake

Pretty good correlation. There are even corresponding upturns on March 14 and 28. 

The hits have decreased, but I hope concern for the victims and the drive to improve earthquake protection everywhere will not.

Friday, April 8, 2011

Tsunamis and the height of the ocean column

The National Data Buoy Center (sorry, no Gurl Center) of NOAA describes the Deep-ocean Assessment and Reporting of Tsunamis (DART) program.  Each DART gauge is designed to detect and report tsunamis, by looking at the pressure of the disturred column of ocean water.

Maps are available here to show the location of these sensors, such as the map below for the eastern side of Japan.

The image below shows the vauation in ocean height for the 24 hours and the 4 minutes surrounding the earthquake.  Note the red onset of the higher frequency changes in ocean thickness on March 11 - that's the origin of the tsunami. It is soon followed by the maximum change of 1 meter, relatively small in the open ocean compared to the wave buildup when it approaches the shore.

For comparison sake, a normal period of four days showing diurnal tidal fluctuations with amplitudes of 0.5 meters looks like this: