The Western Geologist

NASA announced today that they will send a shuttle mission to the Hubble Telescope in 2008 to give it some much-needed repairs. Without the repairs, failing components on the telescope would render it useless. The scheduled repairs will keep it operational through 2013. This is great news for scientists and astronomy buffs everywhere. To celebrate, I give you The Sombrero Galaxy in Infrared Light:



And for good measure, I'll include the Cat's Eye Nebula:

I blogged about the 10/15/2006 earthquake in Hawaii last week here and here.

The image below shows the focal solutions for all of the earthquakes in the NEIC catalog. The focal solution for the Oct. 15 2006 event is shown in red.



The south end of the island seems pretty straight forward. All of the faults strike NE-SW. Thrust faults occur at depth (there's a rough transition at ~10 km, but the shallowest thrust event was 4 km), and normal faults occur above that. I'm picturing something like synorogenic collapse; Hawaii is a very thick pile of material and it's about as tall as it can be, so it makes sense to me that the upper part of that pile is extending. Extension would thin the pile making it more stable (something like the detachment in the upper part of the Himalayas).

The northern part of the island where the Oct. 15 event occurred is more complex. There are two significant thrust events in that area, but they occurred on faults that strike NW-SE (EDIT: I forgot to mention that one of these thrust events was a Mw 5.8 aftershock of the Oct. 15 quake) , or in other words, at a very high angle to the thrusts at the southern part of the island. So, it seems pretty clear that the stress field that's causing the thrust faults on the northern part of the island is different from the stress field that's causing the thrusts on the southern part of the island.

The orientation of the strike slip events in the northern part of the island isn't quite as easy to infer. There are two possibilities. The first is that the faults strike NE-SW (parallel to the faults on the southern part of the island and to the fracture zone that Chris mentioned - the blue line in the figure below). The second is that the faults strike NW-SE (as the lab lemming suggested, parallel to the thrust faults on the northern part of the island (the red lines in the figure below). I think that's more likely. If the strike slip faults strike NE-SW then there'd have to be an along-strike sense of motion (right lateral along part, left lateral along part), which seems physically unlikely. The lines in the figure below represent possible fault orientations inferred from the focal mechanisms:



I also favor a NW-SE orientation for both the strike slip and the thrust faults at the northern part of the island because something similar is observed in other parts of the world. For example, there are active thrust faults that are parallel to the San Andreas fault (a strike slip fault). In that case the two styles of faulting are caused by the oblique convergence of the Pacific and North American plates, so the SAF system isn't directly analogous to Hawaii. However it is an example of two different styles of faulting resulting from the same regional stress field.


I want to speculate now about the cause of the stresses in the northern part of the island. The image below shows the orientation of the P axes from the focal mechanisms (which should be equivalent to the maximum principal stress):




The black symbols are for the southern portion of the island, and they cluster pretty tightly. There's certainly a lot more scatter in the northern portion of the island. So, the stress field in the northern part of the island is a lot more heterogeneous than in the southern part of the island.

There does appear to be some overlap between the northern and the southern part of the island. The trend of the maximum principal stress for the Oct. 15 2006 quake is pretty similar to the trend of the maximum principal stress for the thrust events in the southern part of the island (shown below).



Here's a summary of my thoughts:

1) The thrust faults on the southern part of the island are resulted to the growth of the island, while the shallower normal faults are caused by extension resulting from something analagous to synorogenic collapse.

2) The stress field at the northern part of the island is much more heterogeneous than at the southern end of the island. As I discussed in an earlier message, I'd bet that the magnitude of the minimum and intermediate principal stresses at the northern end of the island are pretty similar. This means that both thrust and strike slip events would occur.

3) Both the thrust and the strike slip faults at the northern part of the island are oriented NW-SE at a high angle to the faults at the southern part of the island.

4) The northern part of the island is subjected to both local stresses related to the Hawaiian islands as well as more far field stresses associated with the movement of the Pacific plate. These far field stresses are swamped by the local stresses at the southern part of the island.

Here's my preferred interpretation of the faults on Hawaii:



The NE-SW faults are associated with local stresses while the NW-SE faults are driven by both local and far field stresses. At least that's my best guess.

From Cognitive Daily comes the Directory of Open Access Journals.

They have 42 journals in their geology section. Worth a look.

Here's my result. I think it was answering 'clam chowder' to the question about my favorite food that did it:

You Are Most Like John F. Kennedy

You live a fairy tale life that most people envy. And while you may have a few dark secrets, few people know them.

HT to Living the Scientific Life

Chris at Highly Allochthonous has a very interesting post about the cause of the Hawaiian Earthquake. I made a quick comment there, and I want to expand a bit on it here.

The USGS fast moment tensor solution for the Hawaii quake looks like a dominantly strike slip event.

That seems weird to Chris, and it does to me too. I'd expect normal faulting to be the dominant mechanism resulting from extension (for the reasons that Chris describes). Before I go on I should point out that the Harvard solution looks more like a normal fault with a bit of strike slip motion. What that mean is that the following attempts to explain a strike slip earthquake in that part of Hawaii may be pointless. But oh well. I'm going to write the rest of this post assuming that the USGS focal mechanism is the better of the two.




Here's a quick map I put together of the Hawaii region (I wish I could plot the individual solutions but that's currently beyond my plotting skills). Earthquakes are from the Harvard CMT catalog (blue is thrust, red is normal, and green is strike slip). I think that these would be the best events to compare to the event on Sunday because the focal mechanisms for all of these event were inferred from teleseismic data (probably from a lot of the same stations).



From that map it looks like thrust events are the most common at Hawaii. That seems a bit counterintuitive to me. That means that the least principle stress is horizontal and the greatest principle stress is horizontal (I'd expect just the opposite since, as Chris pointed out, the Hawaiian Islands are a big pile of rock on the crust – I'd expect them to be collapsing). Despite my misgivings, in terms of stress state switching from a stress state that favors thrust motion to a stress state that favors strike slip motion is pretty straightforward – the least principal stress needs to switch from vertical to horizontal with the greatest principal stress remaining horizontal. Basically the least and intermediate principal stresses need to switch. If they're close in magnitude to begin with then it won't take much for them to switch. I can only speculate about what the perturbation to the stress state was. Maybe motion of magma, stresses imparted from plastic flow in the mantle, or maybe through loading caused by failure along other faults in the time preceding the earthquake (slip on one fault can affect the stress state on neighboring faults).

The map below is of seismicity from Jan. 1 to Oct. 14 2006:



There were quite a few earthquakes, and there were some deep, moderate sized earthquakes (M 3.3-4.7) in the general vicinity of the Oct. 15 earthquake. Perhaps the least and the intermediate principal stresses were very similar in magnitude and those events perturbed the stress field enough to switch them changing the style of faulting (for that event) from thrust to strike slip (of course that's just speculation on my part).

I want to finish with a comment on the greatest principal stress. The orientation of the greatest principal stress inferred from both the NEIC and the Harvard focal mechanisms is the same (~NW-SE). That orientation looks similar to the one I'd infer from the historic NEIC focal mechanisms. It's also similar to the stress orientation from the World Stress Map (which was inferred using focal mechanisms in Hawaii). Since all these events have a common orientation for the greatest principal stress that indicates to me that they're the result of a similar stress field, with the difference being with the intermediate and least principal stresses. As I said above, if the intermediate and least principal stresses are similar in magnitude, then it wouldn't take much for them to switch. That's a long-winded way of saying that I don't think the stresses that caused the Oct. 15 event had to be radically different than the stresses that caused the more common thrust events.

UPDATE: The lab lemming has a new post about the possible cause of this quake.

UPDATE: Editing to correct spelling errors, 10/22/2006.

The part of Texas I live in has been getting hit with a lot of rain. Up to 10 inches in 24 hours. Fortunately our house in on high ground, but one of the two roads to it is not. There was a respectable lake across the road I normally take. Rain storms like this are going to take some getting used to.

A M 6.6 earthquake occurred in Hawaii today at 7:07 AM local time. The summary page from the NEIC is here and a page listing the main earthquake and many aftershocks (including an M 5.8 event) is here.

On the image below the M 6.6 earthquake is the star (you can see from the historic seismicity that Hawaii is a pretty active place):



Here's a map showing the activity today (all of the events are from Oct. 15 except for one from the 11th and one from the 10th):



The earthquake was 39 km deep, and from the moment tensor solution it was a strike slip event, which generally don't generate tsunami (there's not a lot of vertical displacement during a strike slip event so there's not a lot of water displaced):



Here's the shakemap for the event:



The most intense shaking was 6 on the Modified Mercalli Intensity scale which means light potential damage for earthquake resistant structures (things like wood frame houses, modern buildings designed with earthquakes in mind and seismically retrofitted older structures) and moderate potential damage for vulnerable structures (unreinforced masonry, buildings with soft first stories, older buildings) . Here's CNN's coverage. According to them communications have been disrupted, but there are no reports of injuries or building damage. There were concerns about the structural integrity of a hospital there, and new patients were being kept outside. The most significant event CNN reports is an earthquake-related landslide near a major highway.

For comparison the largest historic event in Hawaii was an M 7.9 event in 1868 that resulted in 77 deaths from an earthquake-induced landslide and a tsunami.

Some new preliminary data about whether the North Korean blast was conventional or nuclear from the New York Times:

"An analysis of air samples taken in the region on Wednesday found radioactive material that is “consistent with a North Korean nuclear test,” according to a document sent to lawmakers on Capitol Hill on Friday by the office of John D. Negroponte, the director of national intelligence.

But a senior intelligence official, who spoke on condition of anonymity, said that the results were still preliminary and that final analysis of the data would not be completed for several days."

Hat tip to Dynamics of Cats

UPDATE: Posts at WG about the North Korea test:

Radioactive material detected from North Korea

Guestblog: Teachable Moment: North Korea nuclear test

More recordings of nuclear blasts

North Korea nuclear test

A friend of mine in Japan had a great post abot the North Korean nuclear test at his blog. It's reproduced, with his permission, below:

North Korea announced that they performed an underground nuclear test this week. This is obviously bad news no matter what, but how can we verify that they are telling the truth? That's where seismology can help!

Scientists here at the Earthquake Research Institute just sent out information about the North Korea nuclear test, as recorded by seismometers here in Japan. Take a peak at the seismograms here.

Read more for a quick seismology lesson that explains what they mean.

Here is a brief seismology lesson. Let's begin by looking at a regular, natural earthquake: Click here to view some example seismograms. Earthquakes are sudden releases of energy, a lot like explosions. The seismic waves they release travel through the earth and can be recorded by seismometers literally on the other side of the world. However, it takes time for the waves to travel this distance and some waves travel faster than others. The example link above shows recordings of ground shaking from a number of different recording stations around the globe. Time starts at the bottom in these images and goes up. The line starts out straight at the bottom and then there there is a sudden increase in energy (p-wave) represented by wiggles on the seismogram. Almost all the lines then show a second, larger, burst of energy a few minutes later (further up on the plot). This comes from slower traveling s-waves. It's a lot like a running race where everyone starts at the sound of the gun, but they arrive at the finish line over a certain period of time because some of them travel faster than others.

What are these waves and why are some slow and others fast? Different directions of motion generate different types of waves. Imagine that I am standing behind you with my hands out in front of me and resting on your shoulders while we do a conga line. I can move my arms such that you rock side-to-side, or I can push-and-pull you forward and back in the direction that we are walking. Earthquakes mostly involve "shear motion" caused by sliding along faults (side-to-side motion). Some of you may have seen me use my hands to demonstrate earthquake motion by having one hand slide past the other. Explosions, however, have very little shear energy and produce mostly forward and back blast-like motion. It's easy to imagine getting thrown backwards by the energy of a blast (and fun to demonstrate an explosion with your hands -- they fly apart rather than slide past one another). In an earthquake, you'd more-likely get thrown to the side (relative to the direction of where the earthquake is coming) because earthquakes involve more side-to-side motion. It turns out that the different directions of motion travel through rock at different speeds. I won't go into the reasons why. But this is why there are two main bursts of energy in earthquakes -- the faster forward-and-back motion called P-waves and the slower side-to-side motion called S-waves.

It's important to remember that even though earthquakes have more energy in side-to-side motion, they release energy in BOTH both p and s waves. Why? Even though earthquakes are caused by side-to-side motion along faults, ruptures have ends and there is pushing or pulling near these endpoints that generates some back-and-forth wave motion.

Let's take another look at the nuclear test seismograms. In these, time starts on the left and marches to the right. Each horizontal line is the recording at one location in Japan. Here, there is a lot of background noise before the blast energy arrives, so the line is not perfectly straight on the left side. Most of this background noise is caused by storms and ocean waves and is not actually related to earthquakes or explosions. All of the recordings show a single big increase when the first, fastest waves arrive. Which horizontal line is closest to the blast? The top one because the waves arrive at it sooner. While shaking continues for some time in these seismograms, there is NO second burst. That's because this was an explosion that had very little side-to-side energy, and therefore no s-waves.

Other aspects of the waveform can tell us where the nuclear test site was (the precise location in North Korea) and using some fancy math we can use the amplitude of the waves to calculate the yield of the explosive device. Now you are a trained seismologist and can recognize the difference between a natural earthquake and a nuclear blast. Let's hope you don't have to use this information any more...

UPDATE: Posts at WG about the North Korea test

Radioactive material detected from North Korea

Guestblog: Teachable Moment: North Korea nuclear test

More recordings of nuclear blasts

North Korea nuclear test

I'm definitley arriving late to the party, but I wanted to comment on the story of a group of students at Columbia University who stormed the stage during a speech by Minutemen founder Jim Gilchrist.

Here's a round-up of the coverage:

From Dispatches from the Culture Wars:

here and here

From The Volokh Conspiracy:

here and here.

And finally, from No Se Nada:

here (with a wonderful personal anecdote about Bollinger).

I left a comment at No Se Nada, and I wanted to expand on it here.

I spent a fair number of years at the University of Michigan and Lee Bollinger was president for a good chunk of that time. I remember a few incidents during Bollinger's tenure.

In 2000 a group called the Students of Color Coalition (SCC) occupied the offices of a student society called Michigamua. Michigamua was founded in 1902 and was given a perputal lease to some offices in the student union in gratitude for their fund raising efforts. Some of the ceremonies in Michigamua involved Native American artifacts and references (mockeries?) of Native American culture. Michigamua agreed to stop using Native American artifacts in 1989, but according to SCC they didn't follow through on their promise (SCC also claimed that their name was offensive). SCC occupied Michigamua's offices and hung a banner out the window of the 3rd floor of the union (I don't remember what it said even though I saw it every day on my way to and from the bus). Here's a statement Bollinger made in Feb. 2000:

“For the past ten days, we have been engaged in discussions with students including the students occupying the tower of the Union. We do not believe that occupation is the way to resolve issues within the University. In this instance we felt that it was in the best interests of our educational process for the University to pursue that discussion to a reasonable resolution.

“Any conversation must have starting points. For a University, a fundamental principle is that, with rare exceptions, students, faculty and staff must not be treated differently because of their beliefs or the expressions of those beliefs. That principle has direct application to this controversy. Some have argued that one of the societies using the Union tower space, Michigamua, should be stripped of its University affiliation and lose its exclusive use of that space because it has a history of practices that demean and degrade Native American culture and spirituality. Under our principles it is clear that student organizations must not be recognized or de-recognized, or suffer any other penalty, because the ideas they espouse or beliefs they adhere to are offensive, or even dangerous, to our community. I have spoken to leaders of the groups occupying the tower, other students and faculty, and they, too, value this principle.

“Neither viewpoints nor legacy necessarily entitle any group within the campus to privileged space. We will address, in a neutral way, the process of space allocation among student organizations within the University.

“It must be said, again and again, that responsible membership in our University community implies caring about the perceived impact of one’s actions on others. Of particular importance are perceptions, however unintended, of cultural offense, and those behaviors that cause others in the community to be excluded and unappreciated. Whether conscious or not, practices that negatively stereotype groups in our society cause unjust pain and humiliation. I believe such practices are not acceptable behaviors in a University that values and fosters diversity. We must never take lightly the effects of such perceptions and behaviors.

“Current students of Michigamua acknowledge that its history has included practices demeaning of Native American culture. None of us, however, can count ourselves free of embarrassment and even shame for what we have once believed or practiced, not even the University of Michigan.

“Our students are continually reminding us of the challenge embedded in Pascal’s enduring words, inscribed on the walls of our University, ‘Justice and power must be brought together so that whatever is just may be powerful and whatever is powerful must be just.’ ”

He agreed that demeaning Native American culture is inappropriate, admonished SCC for occupying the office, and didn't take the easy out of condemning the present members of Michigamua for the behavior of past members.

Here's his statement from March of 2000:

"As I stressed in my Statement of February 17, 2000, "practices that negatively stereotype groups in our society cause unjust pain and humiliation. I believe such practices are not acceptable behaviors in a University that values and fosters diversity. We must never take lightly the effects of such perceptions and behaviors." While this University honors the principle that individuals and groups within the University community must be free to express a wide variety of beliefs and ideas, it is also committed to ensuring that its own institutional voice on the subject of racial and ethnic respect be unequivocal. The University simply does not condone practices that denigrate the values or traditions of particular racial or ethnic groups. Finally, it must also be said that the University does not condone the illegal occupation of University premises by any student group.

The recent protests about the Michigamua student organization have raised an important question as to the proper nature and scope of University involvement with student organizations. Accordingly, the panel described in my Statement of February 25, 2000 that is considering the question of privileged space also will consider under what circumstances and in what ways the University, its administrators and faculty members should be associated with such organizations and it will recommend guiding principles in this regard. The University's Executive Officers and I will then decide whether and how to implement such principles.

In considering this issue, the panel will consider the concerns that have been expressed about whether and to what extent associations between the University, its administrators or faculty can or have given rise to the impression that the University endorses racial or ethnic ridicule, and whether and to what extent those associations can or have contributed to marginalizing or disenfranchising other groups or students. The panel will also consider applicable civil rights and anti-discrimination principles as well as applicable First Amendment principles such as freedom of speech and freedom of association.

As with the question of privileged space, the panel will gather public input in a variety of ways including holding public hearings to solicit student, staff, faculty and community member input. The panel will work expeditiously and make its recommendations regarding space before April 13, 2000. The panel will make its recommendation on all other issues before it by October 2, 2000. The decisions the University makes about the assignment and use of the Michigan Union tower and any other exclusively assigned space will be made prior to the beginning of the Fall 2000 academic term. The panel will issue its findings and recommendations on all questions before it in written form, and those findings and recommendations will be published to all interested parties and the public."

In the end Michigamua got to keep their name, but agreed to move out of the Union. Their website is here.

I remember a few other incidents. When the U of M affirmitive action case was just starting there was a flurry of activity on campus. Two of the speakers stick in my mind. Jesse Jackson came to give a talk in favor of affirmitive action (I save one of his placards - I rediscovered it while I was moving out of my office at the end of grad school). Fred Phelps and his group came to protest. I vividly remember an ~five year old boy holding a sign proclaiming "Matthew Shepard is burning in Hell." Despite the disgusting nature of Phelps' group they were allowed to protest unmolested. I also remember a preacher who'd hold up a sign on the Diag and comdemn passing students to an eternity of fire (I know that this was at least a weekly event but I don't remember if he did this more often). He was occasionally heckled, but he was never stopped from speaking. During the 2000 elections the campus Republicans had a table set up on the Diag, and they were even able to hand out collections of G. W. Bush's speeches (I got a copy and had a lot of fun sneaking it on to my friend's bookshelves and seeing how long it took them to notice). I also remember an instance when a group of abortion protestors rented a truck and drove it around campus with pictures of aborted fetuses.

The average person at Michigan was certainly liberal, but it was a place where free speech was encouraged (at least in my experience). Returning to the modern day I was very pleased with Bollinger's statment about the protestors at Columbia University (excerpted below):

"Of course, the University is thoroughly investigating the incident, and it is critically important not to prejudge the outcome of that inquiry with respect to individuals. But, as we made clear in our University statements on both Wednesday night and Thursday, we must speak out to deplore a disruption that threatens the central principle to which we are institutionally dedicated, namely to respect the rights of others to express their views.

This is not complicated: Students and faculty have rights to invite speakers to the campus. Others have rights to hear them. Those who wish to protest have rights to do so. No one, however, shall have the right or the power to use the cover of protest to silence speakers. This is a sacrosanct and inviolable principle.

It is unacceptable to seek to deprive another person of his or her right of expression through actions such as taking a stage and interrupting the speech. We rightly have a visceral rejection of this behavior, because we all sense how easy it is to slide from our collective commitment to the hard work of intellectual confrontation to the easy path of physical brutishness. When the latter happens, we know instinctively we are all threatened."

The students who stormed the stage were thugs, plain and simple, and they deserve to be prosecuted.

Ending on a lighter note The Daily Show covered the event here (hat tip to The Volokh Conspiracy). The best line of the clip is (paraphrasing): "Congratulations protestors, you've managed to make Sean Hannity seem like the reasonable one."

I'm currently a visiting assistant professor. I found out today that I'll be promoted to a tenure track position at the beginning of the next academic year. I also found out that I'll be able to purchase a piece of equipment that I've been wanting for some time (a hand held XRF machine). I've got three projects that have been on hold that I can finish now.

From the Oklahoma Geological Survey:

A 700-1800 kiloton blast from 1992. The largest underground blast since 1976 according to that site. The station was 11420 km from the blast.



For comparison the 1995 M6.9 Kobe earthquake (10600 km from the station and 22 km deep). (note that this seismogram is ~1 hr long while the seismogram from the nuclear blast is only ~20 minutes long).



As I learned in the comments from thread at No Se Nada a sesimogram from a blast is dominated by P-waves. I can certainly see the lack of S waves in the recording from the nuclear blast (assuming they were cut from the plot).

Here's an explanation from LLNL:

"Livermore seismologist Bill Walter explains that the differences in seismic P- and S-wave energy provide one method of discriminating explosions from earthquakes. Seismic P waves are compressional waves, similar to sound waves in the air. Shear (S) waves are transverse waves, like those that propagate along a rope when one end is shaken. Because underground explosions are spherically symmetric disturbances, they radiate seismic P waves efficiently. In contrast, earthquakes result from sliding or rupture along a buried fault surface and strongly excite the transverse motions of S waves. Thus, we expect that explosions will show strong P waves and weak S waves and that earthquakes will show weak P waves and strong S waves, as seen in Figure 2."

Here's the figure referred to in that quote:



The LLNL page also has a good discussion of the difficulties in inferring blast yields from seismograms.

UPDATE: I forgot to give a link to the LLNL page.

UPDATE: Lab Lemming has a couplenice posts on this topic.

UPDATE: Posts about the North Korea nuclear test at WG:

Radioactive material detected from North Korea

Guestblog: Teachable Moment: North Korea nuclear test

More recordings of nuclear blasts

North Korea nuclear test

The North Koreans conducted an underground detonation of a nuclear bomb today.

These are the seismograms of the nuclear test in North Korea (data from the IRIS website.

The first shows the raw data:



This image shows the same data with a regional filter applied (1-10 Hz). I don't know the rationale for applying this filter, but it looks like that's the way IRIS displays their data (can you tell I'm not a seismologist?).



For comparison here are the records from the same stations for a M5.9 event at a depth of 359.5 km in the Sea of Japan (both stations were further from this earthquake than they were from the North Korean test).

This is a plot without a filter.



This is a plot with a filter.



Here's another earthquake for comparison. This one is a M 5.5 event at a depth of 71.6 km that occured near Kyushu.

No filter.



Filter.



I'm not sure how to distinguish between a nuclear blast and an earthquake. To my untrained eye it looks like the North Korean event is more impulsive (for lack of a better word) than the Sea of Japan event. However the North Korea event looks similar to the Kyushu event to me (of course the Kyushu event is much closer in depth to the North Korea event too). I see some differences in the later arrivals, but I don't know if I'm just seeing things.

UPDATES

I forgot to link to the post at No Se Nada that prompted me to look for the seismograms for the North Korean test.

Highly Allochthonous (great name) also has a post.

UPDATE: Posts at WG about the North Korea nuclear test:

Radioactive material detected from North Korea

Guestblog: Teachable Moment: North Korea nuclear test

More recordings of nuclear blasts

North Korea nuclear test