Slow global warming - stop earthquakes!

Last Thursday's journal club was something of a milestone for me - my first even semiformal presentation on a scientific topic since high school, and for an audience of people who already have degrees in (or have already partly completed degrees in, at least) seismology. Journal club is laid back and conversational and not for any sort of grade or credit, which really gave me no good reason to be worrying about it, but I was worried nevertheless.

My job was to summarize seismological happenings in Nature since December, of which there have not been very many. Of the two earthquake articles I found (there was also a volcano article, which I did not realize was fair game until after the presentation), I went a little more in-depth on one summarizing an experiment simulating stick slip events in fault gauge particles using glass beads and low-frequency sound waves. The experimenters built a rig that applied constant stress to the beads, and could apply pulses or prolonged sounds if desired. Without the sound waves, the recurrence interval and stress drop of the stick slip events was constant and predictable, but as soon as one pulse was thrown into the mix, the recurrence interval became unpredictable and the stress drop fluctuated more. The aim was to try and see how a bombardment of long-distance seismic waves across an unrelated fault triggers new quakes, and to see if there was any pattern to it that could be used for the sake of predictions. There was no pattern, and I had a few questions about the method (such as the size of the beads, or whether or not the direction from which the pulses came made a difference on the results), but the consensus of everyone at the meeting was that these were valid questions that hopefully were covered in some supplement to the article somewhere, since these things really shouldn't have been left out.

And it turns out that worrying was, as I should have expected, not a thing I needed to be doing. People asked questions after I was finished, which answered as best I could, and then there was some further discussion of long-distance triggering. It didn't seem to be any more or any less discussion and questioning than after anyone else's presentation that I've seen so far, and one of the faculty told me it was a "very good kind of unremarkable," and that I would have definitely been told if I'd screwed up. Now that I know I've done well once, the next time should be easier.

The other person who presented last Thursday chose to focus in on a paper dealing with carbon dioxide released from faults during large earthquakes. The theory is that there is enough friction in larger quakes to melt a small amount of the rock in the fault, which releases gas. I thought it was an interesting article, but the way the title was worded made it sound like a disastrous global-warming-related phenomenon. I forget the exact wording, but at first glance, it seemed like the article might actually be some far-fetched thing about how faults, when just sitting there, are spewing greenhouses gases. I was glad that was not the actual content, but I have to wonder if the title was carefully formulated to grab attention in a time when global warming is such a focus. It was also certainly good for a long string of "stop plate tectonics" jokes, though we all agreed that volcanic emissions should be targeted for reduction first...

The Tsunami and the Whale

Now that I've pretty much caught up with the load of work on which I procrastinated even more than usual due to last weekend's concerts, I can get back to interacting with the internet rather than just lurking. At least for the time being...

I have two weeks of Journal Club to catch up on here. Both of these weeks involved several people doing overviews of recent journal contents. This broke with the alternating schedule of small papers one week, big paper another week because the professor scheduled to present the big paper had a conflict. This meant I couldn't use reading the seismology paper as an excuse to further procrastinate on the electronic music homework, but it also meant more of an overview of recent research that I'd like to be reading but don't have the time for just yet, no thanks to the impending thesis and comprehensive exams.

The main paper we looked at this week dealt with small earthquakes only, which seems to be a relatively unpopular thing to write about. It makes perfect sense that people would want to focus on the Big Ones, since those are the events that effect society at large and that totally redo the stress balance on a fault system in one fell swoop, but the catalog of hard data (rather than historical description of effects) doesn't really include many of these for any given region. But there are plenty of small ones, and I'm sure there are plenty of studies that could be done on small ones that don't just relate them to big ones. The particular focus of the paper we looked at on Thursday was direction of slip (as in unilateral versus bilateral) and how that effected aftershocks. The largest quake discussed in the paper was a magnitude 4.1, which put most of the aftershocks into the unfeelable range. Looking at a few isolated 4-ish quakes, there did seem to be a correlation between directivity and aftershocks, with unilateral quakes having more aftershocks, which were mostly located within 70 degrees of the rupture plane. Bilateral quakes had fewer aftershocks in a less-confined space. The final example in the paper was a cluster of high-3 low-4 quakes up in the vicinity of the Calaveras Fault and at a pretty deep depth, and that's where the model got a little tricky. Whether each event in the cluster counted as an aftershock of the largest event previous to it or whether the ones close in magnitude counted as separate events was unclear, but those of us in the discussion agreed that the way these events were considered would make a difference in the conclusions. Furthermore, it seemed like the people conducting the study were inconsistent in what they treated as an aftershock versus a separate event, and it looked suspiciously like they might have done this to fit into the 70-degree angle measurement. We all agreed the paper would have been much stronger without the example of the cluster, both for the consistency thing, and also because a different configuration of stress is needed to set off a cluster versus an isolated event and its aftershocks.

Out of all the papers summarized last week, the one that was most interesting to me looked at postseismic slip between a mainshock and a large aftershock. I don't remember a huge number of details about the paper(people go through papers quickly during summary weeks - I've been thinking of asking the person who picked this one where I can find the whole thing), but it focused on a series of events in Japan. The study found a substantial amount of postseismic slip after the mainshock, directed toward the eventual location of the aftershock. These events went down the subduction zone rather than along it. I have to wonder what implications, if any, this observation would have on a creeping strike-slip fault. Could a rupture starting ahead of a creeping section and moving toward it stop where the creep starts, speeding up the rate of creep in the hours following the quake, and eventually set off another event on the other side of the creeping section? I'll definitely be looking to see if there are papers about this.

The other main paper we looked at last week had to do with inferring the size and shape of the area of seafloor displacement in a tsunami-generating earthquake by looking at the tsunami waves and inverting the data. I wasn't quite clear on how this worked based on the brief explanation in the discussion, but it was still a memorable discussion due to an amazing mental image. The professor explaining the paper was describing how DART tsunameters work, and how, unlike buoys, they're stuck to the ocean floor and won't pick up water column changes from surface/storm waves. "Only tsunamis set these things off," he said. "Or if a whale died and fell on one, that might do it, too."
Whale + tsunameter. Is that not fantastic? The mental image kept popping into my head all weekend, even at such inopportune times as the dress rehearsal for the concert (it was all I could do to not crack up). With such persistent visual thoughts, there was really only one thing I could do:

(I'm aware the big wooshy splash thing should be coming off of the whale's whole body. I just became aware too late to undo the coloring. Bleaugh.)
I think I'm going to give the original copy of this to the professor who made the comment, since it's all his fault.

My aftershocks: let me show you them.

I think I'm going to feel anxious about my application to our Earthquake Physics program until I get that official letter, no matter how many good signs I'm getting from people. So far, nobody has said or done anything that leads me to believe I won't be getting in - quite the contrary, really. I don't think a department expecting to reject someone would keep inviting that person to participate in departmental events and discussions, nor would someone on the application committee, when passing me in the hall, go, "We looked at your application today," and give a big grin and a thumbs up. And yet I am still nervous, and have a couple of weeks to go before I get that letter. Ahhh!

One of the departmental functions in which I have been invited to participate is Journal Club. Every Thursday, the EP faculty and graduate students meet to discuss recent research related to a specific theme (this quarter's is earthquake prediction) - this alternates between one person choosing a bigger article which we all read and discuss, or three people presenting shorter articles of interest from a particular journal they've been assigned. I've even been assigned a journal to search; everyone figured Nature would be a good place to start, since it's written to be understood by scientists of all types, not just insiders.

The first meeting of the quarter was this Thursday (I would have written about it that evening if my hard drive hadn't thought Wednesday night would be a fine time to die). We all read an article from Journal of Geophysical Research by K.F. Tiampo, J.B. Rundle, S. McGinnis, S.J. Gross, and W. Klein called "Eigenpatterns in southern California seismicity."

I had an immediate uh oh moment due to not understanding the very first word of that title, but I looked it up and forged ahead with reading anyway. I found it pretty hard to wade through much of the text as well, due in part to some terminology issues, but also because there were a lot of cases of them using really elaborate and circuitous phrasing to describe something not particularly complicated. Basically, what they did was take the catalog of southern California earthquakes and plug it into a computer program that checked, for any given location that has an earthquake on any given day, where else in the region tends to have quakes on the same day (and where else tends to have fewer quakes than usual on that day). Considering the types of patterns they were trying to pick out, one would expect the terms "aftershock," "triggered slip," and "stress change" to turn up a lot, but they really didn't.

But even with my not understanding all of the terminology or the specifics of the method, I was still able to pick up on plenty of hints that this paper is full of it. For one, there were some outright factual errors. There were repeated instances of the Joshua Tree-Landers-Big Bear sequence as having happened in 1991 rather than 1992, which is bad enough in itself, but becomes even more worrisome considering that the arbitrary cutoff date for some of the calculations was the end of 1991. It didn't look like Landers was included in those figures, but some were not so clear. There were also generalizations/assumptions in the paper. The authors stated that Parkfield quakes happen every 22 years, like clockwork, not that the average is 22 years. Big difference! And such statements do not credibility make. Another red flag came up very early in the article, when the authors stated that their goal was to identify "all possible space-time seismicity configurations." All possible? That's lofty and ambitious, particularly when they only have some sixty years of data to work with. You certainly can't come up with all possible patterns in such a small chunk of geological time, particularly not when most of the major faults in the area did not have a major rupture in that span (one would think they'd want to get the San Andreas in on their predictions), nor when there are who knows how many as-of-yet-undiscovered thrust faults whose current inactivity also puts them out of the calculation. I think "all possible" would be impossible even with much more data than this study used, so the fact that they've even aimed for it seems pretty ridiculous. Lastly, when events below magnitude 3.0 were taken out of the picture, or when the time interval they were using to check correspondence was changed, the results came out completely different from each other, a far cry from hard and fast prediction rules.

I came to the Thursday discussion with my low opinion of the article, but I also decided I wasn't going to say anything if everyone else didn't have a problem with the article. I was admittedly quite worried that I was completely off base, but those worries went away when the professor presenting the article started with, "I'm going to present this paper, or at least the parts that I understood." Turns out that everyone else thought the paper was full of it as well, so I felt much better about my reading/comprehension skills and participated in the discussion after all. People pointed out even more inconsistencies and problems, including some tweaking of the scale on the last couple of diagrams to make the results look more significant. We all agreed, though, that the paper would have gotten on our nerves much less if the authors had said, "We tried this method and found no correlation," rather than trying to make a big deal out of a couple thousandths of a percent. No correlation is a perfectly legitimate result to an experiment. Disappointing, certainly, but legitimate. But I guess that's not the sort of result that draws the mainstream media toward your ZOMG Earthquake Predictiashun Breakthrough, and apparently Tiampo et al got a decent share of attention for this paper, so there we go.

Next week is one of the sessions in which three people share shorter articles. It's not my turn yet, since I figured I ought to hold off until I see how it works, but I may volunteer for two weeks after that.