First I've seen of last week's tsunami. Attempt to embed below, but here's a direct link.


Hat tip to my student Al for passing this on. Thanks Al!

Labels: earthquakes, news, tsunami

After yesterday's post on a new feature I found on the USGS earthquakes site, reader Tony Edger asks, "After exploring the USGS website and elsewhere without much success, I am hoping you might steer me to a description of how to read a seismicity cross section. " He was referring to these images:

So here's how this works: the top image is a map. It gives you a "bird's eye" perspective on earthquake locations at the subduction zone near Samoa. It shows you the epicenters (location on the earth's surface above a quake's actual location, called its "focus" or "hypocenter") of many earthquakes, along with Tuesday's big quake, shown with a star. The thick red line is the position of the trench, a bathymetric expression of the subduction zone. The epicenters are color-coded for their depth. Orange and yellow are shallow; green and blue are medium depth; and purple and red are the deepest. Notice that they make a sort of "rainbow" pattern, with the shallowest quakes in the east, and the deepest quakes in the west. This is "looking down" on the subducting slab: it's like we're able to "see" the subducting slab as it descends into the mantle.

The lower image is the cross-section. It gives you a "gopher's eye" perspective on the same data. A cross section is drawn along the line A-A' on the map. This is conceptually slicing the Earth open along that line, then removing half, and looking sideways at the remaining half. Note that the A-A' line is now along the top of the figure, representing the surface of the earth. Along the horizontal axis is horizontal distance, measured in kilometers. Along the vertical axis is depth, also measured in kilometers. The two axes are not drawn to exactly the same scale, but pretty close. In other words, 100 km of horizontal distance is approximately equal to 100 km of vertical distance (depth). The same data are plotted, or at least the subset of the map's data which happen to fall on that particular line, A-A'.

With this new perspective, a side-view, what do we see? Well, there's the star, which shows the depth of the quake that triggered all this discussion, and a whole bunch of other (historical) earthquakes. Now, instead of the epicenter being plotted, we're getting a more robust sense of the hypocenter (or focus). Note that the earthquakes are being generated in a big swath, starting at the surface in the northeast, and dipping down deeper and deeper to the southwest. This line of seismic activity reflects the jerking passage of the subducted slab of oceanic lithosphere. As it plunges down, it generates lots of shaking. This zone of seismicity was first described (independently) by two scientists, Kiyoo Wadati and Hugo Benioff: in their honor, it is referred to as the Wadati-Benioff zone. (Wikipedia has more) Their realization is our gain: we can "see" the subducted plate diving at an angle of 30 to 40 degrees. That's what's so cool about this:

Something that no human will ever directly observe is "visible" to us because we can pinpoint the three-dimensional location of thousands of earthquakes. These bumps and jolts reveal the position of the bumper and jolter: the subducting plate!

Labels: analogies, art, earthquakes, plate tectonics, websites

Perusing the USGS page on yesterday's magnitude ~8 earthquake in Samoa, I found a new feature that I had not previously seen on these earthquake data pages: a cross-section! Check it:

The star gives the location of yesterday's temblor some regional context. This is a super-cool visualization of a subduction zone (in this case, the Pacific Plate subducting beneath the Indo-Australian Plate). I'll be using this image in my upcoming "earthquakes" lecture in Physical Geology. What a beautiful way of visualizing the plunge of a slab of oceanic lithosphere!

Labels: art, earthquakes, plate tectonics, websites

The September meeting of the Potomac Geophysical Society will be held September 17th at the Fort Myer Officers' Club in Arlington, VA in the Campaign Room. This month's talk will be: North Korean Nuclear Test of May 25 2009: Similarities and Differences With Respect to the Initial October 9, 2006 Test, by Jack Murphy (SAIC, McLean, VA).

Abstract:
On May 25, 2009 North Korea announced that it had conducted its second nuclear weapons test. As with the first test, this second explosion was well-detected by the seismic stations of the International Monitoring System (IMS), as well as numerous other international stations operated by the USGS and other organizations. The best relative seismic location for this explosion places it within 2 km of the ground truth location of the initial 2006 test in a mountainous region of northeastern North Korea. Comparisons of the seismic data recorded at common stations from these two tests indicate that the second was approximately four times larger than the first, having an estimated yield in the range from about 2 to 5 kt. While there are many similarities in the observations from the two tests, there are several notable differences. Perhaps the most surprising of these is that there were no reported detections from any of the IMS radionuclide stations. The report of a noble gas (Xe¹³³) detection in Canada tentatively associated with the October 2006 test had led to some optimism that the more complete network of stations operating in 2009 might provide powerful detection capability with respect to clandestine underground nuclear tests. While analyses are continuing, the absence of detections from the May 2009 test has tempered that optimism to some extent. Another unusual aspect of the May 2009 test was the observation of anomalously large long-period surface waves. While the surface waves from the October 2006 were also somewhat larger than expected, the surface wave Ms magnitude value for the May 2009 test places it in the earthquake population on the Ms:Mb discriminant plot, and there has been no convincing explanation offered for this to date. Thus, despite the many years of experience with nuclear test monitoring, there continue to be unanticipated surprises that require in-depth analyses and assessments.

Reception at 6:30. Dinner at 7:30. Talk at 8:30 PM. Allow 15 minutes for security entering Ft. Myer as all civilian vehicles are searched. To ensure access to and from Fort Myer use the Hatfield Gate, open 24 hours a day. If you wish to attend dinner ($25), please make reservations with Joydeep Bhattacharyya at 703-676-4373 or via e-mail. If you wish, please feel free to attend the talk without dinner. Non-members and guests are welcome. Visit the PGS web site at for new meeting announcements, etc.

Labels: earthquakes, korea, meetings, pgs

Last night, I took a group of Honors students to the United States Geological Survey's National Center in Reston, Virginia, for a public lecture by Bruce Molnia about Alaska's disappearing glaciers. The talk was all well & good, but a nice little surprise came afterwards, when Jared noticed a display in the lobby of the Dallas Peck Memorial Auditorium:

That's the classic "ancient Chinese seismograph" featured in so many introductory geology textbooks as the lead-in to their chapters on earthquakes and seismology. Pretty cool to see it in the flesh brass.

The way it works is that each of the little dragon heads projecting off the urn had a little brass ball in its mouth. If it got shaken by an earthquake, that little brass ball would pop out and into the waiting mouth of the little brass frog down below. The frogs aligned with the wave propogation direction would be the ones to be "fed." This implication of the temblor's source direction would allow authorities to direct scouts and relief operations to the appropriate corner of the dynasty.

Neat!

Labels: alaska, earthquakes, gear, glaciation, nova, rept, teaching

50 years and 2 days ago, the Hebgen Lake Fault slipped, and triggered the Madison River Landslide. Here's the article I wrote about it for EARTH magazine.

By the way, someone already pointed out to me that Orion's a winter constellation... d'oh!

Labels: earthquakes, mass wasting, montana

The Berkeley Seismological Laboratory (which initiated an RSS feed a few months back -- well worth subscribing to) has a post up today showing the seismic signals generated by last weekend's Yosemite rockfall. Check it out!

Labels: blogs, earthquakes, mass wasting

Heh heh.

Labels: earthquakes, humor

Nevada's Yucca Mountain site for a proposed nuclear waste repository has lost much of its funding in President Obama's proposed budget. Personally, I think this is a good call - I never thought that the Yucca Mountain site seemed viable for the geological long-term. For a facility being designed to outlast human civilization (warning signs are not written in English, but in sign language that's predicted to still be useful when potential meddlers show up 10,000 years from now), Yucca Mountain is located in too tectonically-active an area for my liking. Basin and Range extension, with associated earthquakes and volcanism, imperils the facility's security over the long-term.

But then where do we put this nuclear waste? We've got more and more of it every day. I'm a fan of nuclear energy because I feel that in spite of the risks associated with radioactive leaks, it's a proven technology that looks better all the time because it produces no carbon emissions. To me, the relatively short-term (local) risk of radiation leaks is outweighed by CO2's long-term (global) risk of climate change. Provided sufficient security, I think it's a great "halfway house" between fossil fuels and 'alternative' energies like solar, wind, and geothermal.

Yucca Mountain has several advantages in terms of its location: it's dry, and it's not in someone's backyard (far from large populations -- though Los Vegas residents might quibble with the definition of "far"). But Nevada's regular seismic shaking (3rd in rank among the U.S. states, after California and Alaska) and the proximity of some young volcanic extrusions make me think it's not so great a spot if you want the waste to stay put. I'm thinking that the best place for nuclear waste would be in the craton, the stable interior of the continent. I'm thinking: Canadian Shield, maybe in Minnesota or Michigan or Wisconsin. The issue there is water: you would be trading tectonic stability for saturation and precipitation.

I'll readily admit I'm not an expert here -- just a geologist speculating on an issue that's more complex than mere geology. What do you think? Where's the best place to store nuclear waste until radioactive decay makes it reasonably safe? Use 10,000 years as your hypothetical timeline, bearing in mind how different the world is today than it was 10,000 years ago.

Labels: CO2, earthquakes, energy, environmental, michigan, minnesota, nevada, volcano, wisconsin

Labels: art, earthquakes, faults, teaching

NPR's Louisa Lim reports on tourists flocking to see Sichuan earthquake devastation in China.

Labels: china, earthquakes, news, radio

When I look back on my four years of undergraduate geology education, the one thing that strikes me as the most important thing I learned is the age of the Earth. It sent my mind reeling to recognize what a huge old planet I was on, and how ephemeral was my own species' time on it. I was a blip, a temporary arrangement of carbon, hydrogen, oxygen, and a handful of other elements that would last a while, and then disassociate. Material and energy passed into me, and out. This kinetic chemical phenomenon known as me would soon pass, and the Earth would keep turning. The human species would reach its zenith, then collapse (or evolve into something else), and the Earth would keep turning. The continents would rift and crash and the map of the Earth would soon be obselete, and the Earth would keep on turning. Climates change, meteors hit, "rivers shift, oceans fall, and mountains drift" (REM, 1985), and still the planet keeps on spinning, keeps on orbiting, keeps on keeping on.

The day I really realized the age of the Earth wasn't the day I heard "4.6 billion" in lecture. It was the day I sat there studying and grasped it internally -- it clicked that it was immensely, unimaginably old. My temporary human mind was a short-time-scale phenomenon, and it was impossible for this small cerebral system to get a grip on the true scale of the planet's age. While I would never really know (comprehend/appreciate) the age of my planet, I tapped into something fundamental that day. Looking back on it now, I'm reminded of John Playfair's words when his pal James Hutton took him to Siccar Point for the first time: "The mind seemed to grow giddy by looking so far into the abyss of time" (1805).

When I made that cognitive leap (by essentially realizing it was impossible for me to fully make the cognitive leap), I got stuck on geology. I connected to the study in a way I hadn't done before. Suddenly I was subject to a dizzying temporal vertigo, as if a layer of flooring had crumbled away leaving me gazing into a bottomless pit. The realization gave a whole new perspective on things, and it was exhilarating. It felt like one of the conversations when you're getting to know someone, and realizing that they are both intriguing and yet never completely knowable. It draws you in, connects you. Without getting too gushy, it's kind of like falling in love. I've been a geologist ever since.

As I learned more, both in school and on later peregrinations around the world, I found that geology was a great traveling companion. No matter where I went, geology was there with me, showing me new things, giving me insightful perspective. I was looking at the world through geology-colored glasses, and finding that it had a lot to show me. The world made more sense on an elemental level. Hills made sense; rivers made sense; mountains made sense. While I couldn't claim to fully understand any of these phenomena, I could claim a connection to them now that wasn't there before. They were no longer random in my mind; they had a place in the overall system, and it took geology to make me realize it.

So this perspective has stuck with me, and it's what inspired me to pitch "geology as a connector" as this month's Accretionary Wedge theme. (Newbies: the Wedge is a semi-monthly geoblogosphere carnival wherein different geobloggers contribute posts organized around a central theme.) I was curious about what I would get, and I didn't want to restrict my peers' submissions by specifying what kind of connections should be written about.

Sure enough, different people interpreted connection differently. Tromping around in the mountains doing geologic mapping yields more than insights into local structure and stratigraphy, as BrianR of Clastic Detritus discusses how his field work has connected him to the messy reality that is nature.

Jess at Magma Cum Laude is starting her first semester as a graduate T.A., and is going to employ a teaching technique that connected her to the pervasive nature of geology: everything that the Earth puts out for the purpose of assembling Oreo cookies. Something as simple as an Oreo can be the vehicle through which students realize the manifold ways they depend on the Earth every day.

Where are the boundaries between sciences? Is geology a subset of environmental science, or physics? Or both? How do we define the different parts of Nature that we study? Using a Venn diagram, Hypocentre at Hypo-theses explores the connections between geology and other sciences, particularly in the environmental realm.

Similarly, Mel uses a diagram to explore connections in her post at Ripples in Sand. How does geology connect to paleontology? Join Mel in looking at the taphonomic bridge. (And wish her congratulations on her wedding while you're at it!)

Joining the crowd in her first Accretionary Wedge post, A Life Long Scholar (at The Musings of a Life-Long Scholar) makes a connection between the very small and the very large. In trying to answer questions about massive tectonic plates, sometimes geologists must turn to little bundles of mass a few micrometers across. Check out her post to see how garnets can reveal the secret histories of the continents.

And then there are the personal connections. In Looking for Detachment, Silver Fox was the first one to submit a post on the "connection" theme with her description of how different members of the mining and exploration community connect to one another over time and space (Nevada, of course). How do Charles Manson, Kevin Bacon, and exploration geologists all fit together? Read her post to find out.

MJC Rocks of the Geotripper blog has contributed a real treat: an exploration of the connection of geologists teaching geologists through time. It turns out that his academic lineage goes all the way back to Agassiz and Cuvier! A pretty impressive consideration which will surely inspire the rest of us to investigate our own geologic pedigrees.

Finally, over at Harmonic Tremors, Julian shares a story of how his knowledge of geology led him to make a personal connection with one of his cinematic idols, director Brad Bird. If you've seen the Incredibles, you're familiar with Bird's high quality entertainment. When Julian heard that Bird was working on a movie called 1906 about the great San Francisco Earthquake, he wrote a letter to clear up some inconsistencies in the book upon which the movie is based. The talented director took the time to write back to Julian, thanking him for the "seismic tutorial."

Enjoy the various and sundry posts -- follow these digital connections to other geologists in other parts of the world, and feel connected to the larger community of earth scientists. Thanks to everyone who contributed. If I've missed anyone or if anyone wants to submit a late post, give me a shout or post a link in the comments.
________________________
References:
Playfair, John (1805). Transactions of the Royal Society of Edinburgh, vol. V, pt. III.
REM, (1985). "Feeling Gravity's Pull," Fables Of The Reconstruction, IRS records.

Labels: blogs, earthquakes, field trips, geology, metamorphism, minerals, mining, movies, plate tectonics, teaching

On Monday, my Physical Geology students and I experienced a magnitude-2.0 earthquake during our final exam. The hypocenter was 1 km south and 6km down.

I pulled out the geologic map of the Annandale quadrangle (1986) by Avery Drake and A. J. Froelich to check for faults in that area. Here's a scan of the map:

You can see our campus in the northwest, and I've highlighted the epicenter of the quake with the red and green concentric circle. Interstate 495, the Capitol Beltway runs north-south through the center of this area. To the south and east of NOVA's campus, you can see that there's a mappable thrust fault (the Red Fox Thrust) which dips to the northwest, presumably under the epicenter and under the campus. However, the map provides no information on the angle of dip of this thrust. Is it steep enough to get to 6km depth a mere ~3km north of its surface trace? (The map's cross section shows it dipping at about 52 degrees, but that's pretty speculative.) Or if the dip is shallow, is there a deeper (perhaps parallel) thrust underneath it? (There is none shown within the map area, though there is one to the north of campus that dips to the north -- making it unlikely to be the culprit.) Alternatively, was Monday's quake caused by a new fault? Perhaps a normal fault which cross-cuts these Paleozoic thrusts?

No new answers -- only more questions...

Labels: earthquakes, news, nova

A quick update here on yesterday's "final exam" earthquake:

The USGS has upgraded the magnitude to 2.0, which seems more in line with what my students and I felt. They have also indicated the depth of the hypocenter as being about 6 km.

Talking to other faculty over the course of the day yesterday, I learned it was felt strongly across campus. Hardly surprising, considering we were essentially on top of it. My colleague Nancy Chamberlain wrote me an e-mail describing her experience: "It was a bang, a shake and a rattle. I flew out of my office exclaiming an earthquake... I was told someone dropped something upstairs but it really was an earthquake! I grew up in California and 10 miles off the New Madrid fault in St. Louis... I know an earthquake when I feel one!"

The Survey has also posted a few additional maps. For instance, to establish context, consider this map of historical seismicity in our area:

Labels: earthquakes, nova

Three-quarters of the way through my Physical Geology final exam this afternoon, the room shook and a low rumble propagated through our building. The students, many of whom were in the area on 9/11, instantly looked up with a very concerned "Was that a bomb?" look on their faces. To assuage their fears, and because I've previously heard similar rumbles coming from our HVAC ducts, I told them that it was just the cooling system, and not to worry.

Turns out I was wrong: it was a small earthquake with an epicenter about 1 km from here (we're about 1 km west of Annandale proper, and the USGS suggests it was 2km southwest of Annandale; see map below).

Almost on the epicenter of our own little quake! For us east-coasters, that's a big deal!

WTOP reported on it (Thanks to Ron Schott for forwarding me this link).

Here's the USGS quake page on the event.

Here's the Maryland Geologic Survey's seismometry. (source of image above, which is in Eastern Standard Time, not Daylight)

Here's the Washington Post's (brief) treatment of it.

I've gotta say, Ron Schott's up on it -- within an hour of the seismic event, he had e-mailed Tuff Cookie and I to ask about it. Pretty prompt! Thanks, Ron.


Update: Here's the Google Map showing the epicenter (green arrow). I've circled the building where I was giving the exam in the green circle:

Also: Here's the intensity map as it looked after I logged on and completed the "Did You Feel It?" survey:

Labels: dc, earthquakes, nova

Breaking News: Series Of Concentric Circles Emanating From Glowing Red Dot

Labels: earthquakes, humor, tv

Several websites are dedicated to monitoring Earth's seismicity over time. They make an interesting comparison in terms of graphical representation, considering that they are all reporting on the same information. Check them out and decide which one you think does the best job.

Earthquake Watch is a homemade site using Google Maps to show quake locations and magnitude. It shows magnitude, but only quakes in the last day, without differentiating between quakes in the past hour and longer times. Because it's done using Google Maps, it can be centered wherever you want -- or wherever the earthquakes happen. This is in contrast to the next two options, which have a fixed map centered on the Pacific Basin.

The USGS uses a nice physiographic map as the base for their information display. A series of colored squares of different sizes show magnitude and time of the quake. This is an advantage over the first site: more information revealed in the same amount of space. Still, like the first site, the map is small -- roughly 40% of the total "real estate" available on the screen.

The IRIS Seismic Monitor is my favorite of the bunch. It has a large map (~70% of the screen) with blinking circles of different sizes and colors show information about when a quake happened: last hour, last day, last two weeks, and the past five years. It also offers an option for a huge map (larger than the whole screen). Additionally, it offers a global night shadow -- so you can see which portion of the planet is in daylight, and which half is sleeping through the night.

Labels: earthquakes, graphics