This video was posted on the California Academy of Sciences website. Here Harold Tobin explains the goals of the NanTroSEIZE drilling project and how it ties into the larger picture of earthquake hazard assessment. This ship was also used during the JFAST project to drill the Tohuku earthquake fault. I’ve posted about the JFAST project before and here or learn more from their official page.
Following the M6.3 L’Aquila earthquake in April of 2009, Italian seismologists and government officials were indicted for multiple accounts of manslaughter. The scientific community responded with widespread criticism.
The events leading up to the conviction, the conviction itself, and implications for the scientific and hazard-risk assessment communities was thoroughly summarized by Austin Elliot on his blog The Trembling Earth.
Please take some time to read his take on this event: http://tremblingearth.wordpress.com/2012/10/23/conviction-of-italian-seismologists-a-nuanced-warning/
So my last post was a tiny tiny update. I should write more about what I’ve been up to the past month and a half. First off, this has been an incredible adventure. Namibia is amazing. This was my second time to Africa (South Africa and Namibia). I’m currently living in the Geo department flat at UCT. Thank you to the department staff, and Tanya and Jacq for helping Ben and I get settled.
EDIT: Click any of the pictures below for a larger view!
I know, I know, you want to see rocks. Bear with me. Let me give you some context.
So where in Namibia was I? Where the hell is Namibia!?
Let’s zoom in:
|That’s about 200km South-Southeast of the capital city of Windhoek as the crow flies.|
The Naukluft Nappe Complex is a thrust fault system associated with the Damara Orogen (~550Ma) that emplaced meta-sedimentary rocks in a roughly Southeast vergence on undeformed basin sediments. This area was originally studied by two German geologists, Henno Martin and Herrmann Korn, in the 1930s. These two geologists would later live two years in the Namib desert hiding (and mapping!) during World War 2 (blag post on that coming soon). They divided the complex into three different nappes, though more recent mapping has established five nappes. Korn and Martin also made the observation of a fault rock they describe as the “Unconformity Dolomite”. You know how geologists love to name stuff. First it was “Unconformity Dolomite”, then other authors called it “Lubricating Layer”, then other authors called it “Sole Dolomite”. From now on let’s agree to stick with the sole dolomite convention.
Carrying on, this sole dolomite is the a layer of rock that separates the footwall sediments, blue limestone and shale, from the hanging wall, which is a charlie foxtrot of dolostone, quartzites, and shales. Want a photo of what this thrust looks like? Check out the header for this blog! Oh, you’re too lazy to scroll back up? Okay, here you go:
and at another location:
Did you spot the fault yet?
I have so many pictures of this thing it is ridiculous. Tons of panorama shots too. Sadly, the GigaPan uploader can’t get through the UCT firewall, so we’re all going to have to wait until I’m back in Montreal to see those panoramas. It’ll be worth the wait. I’m getting ahead of myself.
So what does this sole dolomite look like? It’s the brown-tan bed on the blue limestone in the above photos, but let’s move a little closer…
|Ben (Dr. Choff) for scale|
The limestone at the fault margin is mylonitized. Enough teasing, let’s look at the rock.
As you can see there is a foliated zone of dolomite at the fault surface. How about that rock above it though? That’s called “Gritty Dolomite.” It is a “cataclasite-like” fault rock that has dolomite phenocrysts, lithics, and silica. It looks like this:
|Gritty dolomite with silica banding.|
But sometimes it looks like this:
|Discrete gritty dolomite layer between sole dolomite (below) and a dolomite breccia (above).|
Or even this:
|Uhm, what? Laminated and folded (flow-folds?) gritty dolomite. Some silica banding.|
But sometimes it does this:
|Footwall limestone clasts in a gritty dolomite / sole dolomite breccia. A brown silica cortex surrounds footwall clasts.|
And how about up on the ridge (picture from this blog’s header and picture #2)… BAM!
|That is a RocknRoll breccia if I’ve ever seen one.|
Sometimes the gritty dolomite will inject upsection/downsection off of the fault, sometimes looking like this, often found with neocrystallized dolomite, sometimes doubly-terminating neocrystalline quartz on the surface:
|This rock is from part of a clastic gritty dolomite injection.|
And these photos are only on the eastern side of the nappe. Okay, okay, so WHAT were we doing out there? We were mapping this fault with a pair of these:
|Ben desires more satellites.|
The Trimble GeoXH. We set one up as a base station. The other is a rover. We walked the fault, making observations, taking measurements, ect. Once home I load the rover file with the corresponding base station file into the Trimble TerraSync software and presto! Centimeter GPS accuracy! As a first order question, I’ll be looking at how the geometry of the basal fault relates to the type of fault rock observed, injections, and make interpolations of the fault surface.
In the eastern side of the Nappe typical fault dip is betwee 15-25 degrees, but varies widely. Now on the West side…
|Tsams Ost locality|
Can you spot the fault? Hmm… that looks a bit different. Typical fault dip here is ~3 degrees. The foot wall is typically blue shales, and there is no gritty dolomite to be found. We do observe the occasional footwall shale injecting up into sole dolomite…
|Footwall shale injecting up into sole dolomite.|
There’s also some fantastic folding in the hanging wall.
|Hanging wall folds.|
I feel like I could continue on and on posting pictures, so I’m going to force myself to stop. I’ll put up a gallery of photos on my Google+ page in the near future. I’m incredibly eager to get back to Montreal to look at the GPS data and start piecing this puzzle together.
Special thanks to Ben Mapani for his invaluable assistance and advice. Thanks to Ben Melosh, Jodie Miller, Clint Isaacs, Rangers of Tsams Ost, and my advisor Christie Rowe. An extreme thank you goes out to the Naukluft 9 park staff for their generous hospitality and assisting with charging of our GPS batteries.
The scientific ocean drilling ship, Chikyu set a new record for length of 7740 m below sea level for scientific ocean drilling! Christie Rowe has written an article on the work done and work to come as the science team starts pouring over the data. Check it out below.
Right now my advisor, Christie Rowe, is located at the orange dot in the above picture. What are a bunch of earth scientists doing on a boat off the coast of Japan? They’re drilling with the goal of piercing part of the fault that slipped during the Tohoku earthquake (M9) of 2011. That earthquake had a fault slip of approximately 50 m (Lay et al. 2011) that caused a devastating tsunami. The Japan Trench Fast Drilling Project, or JFAST hopes to drill into the fault at the plate boundary.
The drill site is located at a water depth of 6910 m and the researchers hope to drill 1000 m below the sea floor. These depth goals put the Chikyu research vessel on record setting waters. The awesome thing is that GPS transponders on the sea floor at the drill site allow the Chikyu to be positioned within 3 cm accuracy above the drill site. Science rules.
The drilling has two main goals. First, the recovery of fault rock samples. Check out this blog post by Christie Rowe for why we care about fault rocks. The fault rock core will provide insights into the nature of seismogenic earthquakes, which can be compared with what we know about ancient fault rocks exposed in the field. Second, the fault will be instrumented to record the residual heat, fault permeability, and fluid/rock chemical properties. The residual heat will be used to gain insight into the frictional strength of the rock.
Follow along with developments here: http://www.jamstec.go.jp/chikyu/exp343/e/report.html. The researchers are required to blog.
I posted a link to this talk back when it was streaming live and now it’s finally up for viewing. Dr. Jamie Kirkpatrick, a post doc at UC Santa Cruz, gave a talk at the USGS on pseudotachylites and how we can glean information about past earthquakes from the rock record. Watch the talk here.