I love brittle deformation

This is just a teaser from some rocks in Africa that I cut today. Clasts are an ultramylonite.

Advertisements

Flipping the Iceberg

Since I don’t have any posts planned until next week, here’s a quick one to get us to the end of the week. I recorded the above video while on a grad trip exploring the diverse geology of Newfoundland. This was at Seal Cove (21U 543540.42 m E, 5531775.12 m N), near Bay Verte. We got to see an iceberg calve, then this one flipped. I started filming about half way through.

The geometries of the underside are fascinating, not what I would have expected at all. It was an incredible experience to watch it rotate to a new equilibrium. And when sunset came…

Sunset at Seal Cove, Newfoundland

Sunset at Seal Cove, Newfoundland

LaTeX Tables Primer

I held off on posting this so that I didn’t have too many LaTeX posts in quick succession. Grab an effective LaTeX template, or learn why you should start using LaTeX.

So you’ve started using LaTeX, but you’re stuck trying to put your data into a table. Tables in LaTeX are THE most un-intuitive, poorly designed part of the otherwise slick and clean document prep software. When I first tried putting tables into docs, I did everything I could to avoid making tables. Eventually, importing snipped word/excell tables into LaTeX as images just wouldn’t cut it. I had to make a table.

So let’s get started. Open up a new LaTeX doc, I’m using my custom template that you can grab HERE. Get rid of the table of contents and the second section code. We’re going to begin by setting the bounding code that will tell our table how to look:

begin{table}[ht]
        begin{center}
                  begin{tabular}{| c | l | l |}

                  end{tabular}
        end{center}
caption{small{Look at this bitchin’ table!}}
label{table}
end{table}

After begin{tabular} there is a bracket with {| c | l | l |}. This code tell LaTeX how to justify text/images within columns and where to draw vertical lines separating columns. This gives you infinite freedom in how you want to design your table. You can make anything from this:

to this (using code {| c | l  r |}:

Why I’m keeping track of what my neighbor eats, aside, we have two very different tables from only a little change in code.

So now that we have our table style made, let’s input some data.

begin{table}[ht]

        begin{center}
                  begin{tabular}{| c | l | l |}
hline
                                      Bills & Amount & Paid?
                                     Rent & $475.00 & Yes
hline
                                     Electricity & $16.00 & Yes
hline
                                     Water and Gas & $30.00 & Yes
hline
        end{center}
caption{Look at this bitchin’ table!}
label{table}
end{table}

                  end{tabular}

Okay, let’s walk through the code. hline makes a horizontal line the width of your column. Column width is governed by th elength of text you have in a specific column, more on that later. Columns are separated from one another using the & command. The double backslash you see at the end of each line tells LaTeX to start a new row. We can separate rows nicely(and close off the bottom of our column) with another hline command.

So let’s talk about the problems with LaTeX tables. If we take a column with a lot of text in it, like…

begin{table}[ht]

        begin{center}
                  begin{tabular}{| c | l | l |}
hline
                                      Bills & Amount & Paid?
                                     Rent & $475.00 & Yes
hline
                                     Electricity & $16.00 & Yes 
hline
                                     Water and Gas & $30.00 & Yes
hline 

                                    Money I owe my neighbor for walking my dog while I was on vacation in Tahiti enjoying cheap beer and beautiful women while soaking in the sun and laughing at how my neighbor is cleaning up after my dog & $20.00  & No 

 hline
        end{center}
caption{Look at this bitchin’ table!}
label{table}
end{table}

                  end{tabular}

…will give us something like this:

Not bitching.

So how do we fix it? What we have to do is look at the pdf and make an educated guess at around what word we need to start a new row. Once we have that word, we type “& &” then to bring it to the next row.

The double “and” command tells the table that we’ve made it to the far side of the table, but we want those last columns to be blank.

The double backslash drops us to the next row.
So with this code:

begin{table}[ht]

        begin{center}
                  begin{tabular}{| c | l | l |}
hline
                                      Bills & Amount & Paid?
                                     Rent & $475.00 & Yes
hline
                                     Electricity & $16.00 & Yes 
hline
                                     Water and Gas & $30.00 & Yes
hline 

                                    Money I owe my neighbor for walking my dog while I was & &on vacation in Tahiti enjoying cheap beer and beautiful women& & while soaking in the sun and laughing at how my neighbor is& & cleaning up after my dog & $20.00  & No 

 hline
        end{center}
caption{Look at this bitchin’ table!}
label{table}

  end{tabular}

end{table}

                

 We get this:

bitching.
So use to divide up text and make your table the appropriate size. Don’t forget to add in & & for blank columns.
There ya have it, LaTeX tables are annoying to make, especially when you have a large amount of text for each column, but now at least you have a fighting chance of making it work.

#Sciwrite update: Week 2

It’s been two weeks since Anne at Highly Allochthonous posed her writing challenge. Last week I posted a backwards calendar for what I need to get done before the AGU Fall meeting:

December 4th, 8am: Fly out to San Francisco for AGU.
December 3rd, 5pm: Department Christmas party. Definitely no work is getting done after this. Must be packed for AGU, and cook a dish for the party. Manuscript should be done and off my desk.
December 1st: Abstract done. Off my desk for revision.
November 25th: Poster deadline for AGU print services. Poster must be completed, reviewed, completed again. Includes all new data, figures, ect. This is the BIG ONE.
November 14th: Discussion will be written. After this I’m going into 100% poster mode to get my figures done.
November 12th: Results and Interpretation will be re-written to incorporate new data.

So how did I do?

I didn’t quite have my results and interpretation finished by the 12th. As for my discussion, got that finished last night.

Even though I’m making progress, I feel a little behind schedule because I’ve been putting of making the figures I need, pretty and publishable. This is a time consuming process, because I want my figures to be awesome.

How’d you do on your #Sciwrite goals?

The Charlevoix Impact Crater

Figure 1: Aerial radar of Charlevoix impact crater.

Special thanks to field trip leaders Alain Tremblay and Francine Robert

Last month the Canadian Tectonics Group (CTG) held their annual meeting at Charlevoix, Quebec, the site of a Devonian [Lemiux et al. 2003] impact structure. The field trip portion of the meeting centered around learning about and seeing impact structures in outcrop.

This post feature some impact structures we observed while cutting a transect (Figure 2) from the center of the impact crater (mylolisthenite) to the crater rim (normal fault with backthrusting).

Figure 2: Locations of impact structures. White dots outline approximate crater rim.
Setting and background
The impact structure, 54Km in diameter [“Charlevoix”], is approximately half-exposed. The other half is under the St. Laurent River (Figure 1,2,3). The crater straddles the cystalline Grenville province, the Cambrian-Ordovician sediments, and accreted Appalachian Orogen. Supra-crustal faults make up the impact cratering. Major fault systems trend Northwest and Northeast, consisting largely of normal faults. Polymictic breccias provide the best evidence form impact, though other impact related rock types are present (cataclastic gouge, pseudotachylite, shatter cones) [Lemiux et al. 2003]. 
Figure 3: Digital Elevation Model with epicenters Lamontagne et al. (2000)
The St. Laurence fault trends Northeast and is associated with Late Proterozoic early Paleozoic Lapetus Ocean rifting. The fault is relatively undeflected within the impact structure, suggesting post impact reactivation [Lemiux et al. 2003].

Impact Rocks

Shattercones. 19T 408942.00 m E, 5263137.00 m N
Figure 4: Shatter Cone. Lineaments point in the direction of impact.
At this stop we observed shattercones on many scales in limestone and mudstone. The lineations on a shatter cone point in the direction of impact. Basically a shock wave travels through the rock, creating a network of fine fractures, often arranged in a conical shape (Figure 4).

Along the railroad tracks, heading back to the parking lot, shattercones could be observed in coarser grained crystalline rock. This was a great opportunity to show how much better formed shattercones are in fine grained rock vs. coarse grained.

Mylolisthenite.  19T 407510.00 m E, 5260539.00 m N
Figure 5: Injecting Mylolisthenite. 
What, you’ve never heard of mylolisthenite? The term mylolisthenite is used to distinguish a specific type of breccia. It is pale grey to green (Figure 5), fine grained, breccia contained various clasts within the non-fused matrix (differentiating it from pseudotachylite), even though melt fragments can be found within the rock [Rondot, 1989].

Here we are in the inner ring of the crater, beside the center peak. Our location during impact is within what is known as the transient bowl, just below the impact surface.

Soft-Sediment Deformation. 19T 409437.00 m E, 5267768.00 m N
Figure 6:  Refolded sheath fold?

Here we saw some crazy sediment deformation on various scales (Figures 6, 7). This outcrop was previously interpreted as an undersea debris flow. I don’t think the group came to a consensus on whether this was from gravity slope slumping or a result of impact. We did agree that the formation was VERY wet during deformation.

Figure 7: Soft Sediment Deformation

Breccia. 19T 410858.00 m E, 5271299.00 m N

Figure 8: Breccia in crystalline basement.

This area is near a large open fold, presumably related to impact. This breccia could be of tectonic (St. Laurent fault) or impact origin (Figure 8).

Normal fault with backthrusting. 19T 414296.00 m E, 5275355.00 m N

Okay, I know that sounds crazy… but hear me out. First off, I tried to stitch together a panorama of this whole outcrop that I could annotate, but Photoshop was giving me trouble stitching it together. So instead he’s some pictures.

Figure 9: Drag folds, apparent normal motion.

… and a bit to the right, along this outcrop…

Figure 10: Backthrust fault. 
… and just a bit further along the outcrop (please forgive the distortion)…
Figure 11: Backthrust (far-left side) and open folds.

Two hypothesis were presented for this outcrop. The first being that these quartzite beds were thrust up onto the crystalline basement. The second being that these are drag folds (Figure 9) associated with normal motion of the crater collapse. I support the normal fault hypothesis, here’s why.

When a crater impacts, a transient bowl is created. This bowl then relaxes, collapsing downward, creating normal faults along the crater rim.

What about the backthrusting and folding? Typically when normal faults are observed, they are associated with an extensional stress regime, and are the result of accommodating this extension. Here though, we have a semi-sphere bounded area. Extension isn’t being accommodated, collapse is. So even though we have normal motion at our crater margins, there is local shortening as this material collapses into the crater (Figure 12), giving rise to the backthrust and open folds (Figures 9, 10, 11) observed at this outcrop.

Figure 12: VERY simplified cartoon (not to scale) demonstrating crater collapse with local shortening as material is transported into the bowl. Cartoon adapted from Figure 5c of Melosh (1999). Dashed line is crater rim prior to collapse. Blue line is final geometry of crater. Red lines and accompanying arrows are faults/material motion.

References:
“Charlevoix.” Earth Impact Database. PASSC, n.d. Web. 8 Nov 2011. <http://goo.gl/qT2t3&gt;.


Melosh, H. J., and B. A. Ivanov. “Impact Crater Collapse.” Annual Review of Earth and Planetary Sciences. 27.1 (1999): 385-415.

Lemiux, Yvon, Alain Tremblay, and Denis Lavoi. “Structural analysis of supracrustal faults in the Charlevoix area, Quebec: relation to impact cratering and the St-Laurent fault system.” Canadian Journal of Earth Sciences. 40.2 (2003): 221-235.


Rondot, Jehan. “Pseudotachylite and mylolisthenite.” Meteoritics. 24. (1989): p320.

Why is Simon Winchester giving the keynote address at AGU?

I wanted to get some more blog post done before AGU, but that just ain’t gonna happen. This’ll be my last post until the conference. Enjoy!


First some recap, if you’re familiar with the Simon Winchester-Earthquake fearmongering debacle, skip this section.

Back in March Simon Winchester, a popular science novelist, wrote an article published in Newsweek Magazine threatening that the next “Big One” earthquake was due to strike San Francisco. His article caused quite an uproar in the geologic and scientific communities. Simon cited several “facts” that he contrived to support his ideas, mainly that there had been three damaging earthquakes: Christchurch (2/22/2011), Chilean (2/27/2010), and the Japan quake (3/11/2011) in three corners of the Pacific Plate, “…leaving just one corner unaffected–the Northeast.” He goes on to state that strains in the San Andreas Fault beneath San Francisco have built up to “barely tolerable levels.” He also loosely calls upon the idea of earthquake cascading, or triggering of earthquakes by previous earthquakes, using a vibrating brass bell analogy.

Anyway, so the “evidence” in his article, and the fear-mongering tone of his article caused quite a stir in the scientific community. My adviser, Christie Rowe, was at the forefront of this discussion, corresponding with Simon, and writing a rebuttal article for Scientific American.
The main problem isn’t that Simon was stating that an earthquake will hit San Francisco. Many of us have seen the USGS Bay Area hazard map, putting a 63% probability of a 6.7 or greater magnitude quake in the next 30 years, likely along the Hayward fault (which has had two small events in the last month). 
The problem lies in his methods. Not only does Simon make large geographical errors, but he also has no evidence. It’s not science. Many people have already covered this, so I don’t want to belaber the topic. The blog Life’s Little Mysteries has a great article on the topic in which they interview David Schwartz, Head of the San Francisco Bay Area Earthquake Hazards Project. Schwartz provides a great rebuttal to Simon’s cascading theory, “When an earthquake happens, it changes the stress in the [local] vicinity around it, and if there are other faults nearby, this increase in the stress can trigger them and produce more earthquakes. In other places, it relaxes the crust and puts earthquakes off.”
The AGU Fall Meeting

Strangely enough, Mr. Winchester is the keynote address at the AGU Fall Meeting this year (Monday, Dec. 5th). I’m not sure why he was invited, considering the flack he got from the scientific community in response to his article. Perhaps this is a ploy by AGU to get Simon face to face with his discreditors and make him answerable to his statements. Maybe Simon will publicly repeal his article and put forth something that has scientific backing?
Either way, I’m eager to see his speech. Who knows, maybe we’ll get to see the mud fly. 

[Solved] Adobe Illustrator won’t save to PDF

I’m making this post because I recently ran into this problem when making some last minute changes to a poster. When I went to save my .ai document as .pdf, Illustrator would hang/freeze and then crash. Some googling on the topic eventually led me to the solution.

The trouble lies in corrupt preferences settings. Not sure how this file got damaged, but the fix is simple. First, locate your Adobe Illustrator settings. For me (windows machine) I found it in my *hidden* AppData folder.
C:UsersThorAppDataRoamingAdobe



Make sure Illustrator is closed and locate the folder “Adobe Illustrator CS4 Settings” and delete it. I made a back up copy just in case something went horribly wrong, but deleting this should be fine.

Then hold down Ctrl+Alt+Shift when you open Illustrator. A dialog may pop-up saying something about the preferences. Now that Illustrator is up and running, open your document and try saving to .pdf. Problem should be solved!