The Oklahoma Earthquakes

A post by Chris RowanThere was some slight seismic excitement over the weekend in central Oklahoma: a magnitude 4.7 earthquake shook things up early on Saturday morning, which turned out to be the prelude to magnitude 5.6 tremor late Saturday evening. The focal mechanisms (4.7, 5.6) are similar, show largely strike-slip motion, and according the Oklahoma Geological Survey, apparently occurred on a known subsurface fault, the Wilzetta fault, which has an east-northeast trend. Both earthquakes are consistent with dextral strike-slip on this fault, with the northwest side of the fault moving right (NNE) relative to the southeast side.

Focal mechanisms for the two largest earthquakes that shook central Oklahoma on 5th and 6th November. Both show right lateral strike-slip motion, and appear to be due to motion a known subsurface fault (the Wilzetta Fault). Map source: Leonard Geophysical Laboratory

The Wilzetta fault is part of a belt of ancient, buried thrust faults that runs through central Oklahoma and north into Kansas (this pdf is the best resource I found). This thrust belt was first active in the Carboniferous period, 350-300 million years ago, in the later stages of the continental collision that formed the Appalachians. Even when the tectonic forces that created them have long dissipated, faults are still weak points in the crust; and even far from an active plate boundary, the motion of tectonic plates across the mantle can generate stress. If that stress is aligned in the right direction, the scars of ancient orogenies such as the Wilzetta fault can still respond to them, generating earthquakes large enough to cause some damage.

Earthquakes are certainly not unknown in Oklahoma, and another reactivated thrust fault in the south of the state, the Meers fault, produced a strong enough rupture some time in the last millenium to produce an impressive scarp. But these two earthquakes, and a magnitude 4.3 in the same region last October (which had a similar focal mechanism) are three of the four or five largest tremors recorded in the last 150 years or so: lower-level seismic activity has also clearly ramped up in the last three years, with many more earthquakes in central Oklahoma that you would have expected based on records of the past century.

Earthquakes in Oklahoma, 2006-2011

Earthquakes in Oklahoma since 2006. Note the sharp uptick in the past 3 years (click to enlarge). Source: Leonard Geophysical Observatory.

This fact does not mean that we could have predicted the weekend’s earthquakes, although I suppose it makes having them here less surprising that in a region which has remained totally quiet seismically. I do find myself pondering Seth Stein’s ideas on how earthquakes in plate interiors might be more distributed, with the locus of activity shifting between different regions over time.

For more on this earthquake, check out blogging from the The Trembling Earth, Paleoseismicity and Seismo blog, amongst others. I also highly recommend taking a few moments to appreciate this cool animation of the seismic waves generated by the biggest earthquakes propagating through the Earthscope transportable seismometer array. And possibly even cooler than that, all the birds and insects that were startled into the air when the shaking started were picked up on radar. Radar! Science is really awesome sometimes.

Categories: earthquakes, focal mechanisms, tectonics

Writing Challenge, Week 1: Are you making progress?

A post by Anne JeffersonIt’s been a week since I issued the initial challenge to join me in a month-ish of intense writing activity. I’ve seen use of the #sciwrite hashtag pick up on Twitter, and 41 of you have now publicly committed to the project. As promised, here is a weekly check-in post documenting my progress and struggles during the week, and asking you to share yours. My update is below the fold, and I hope you’ll share yours in the comments here or on your own blog, with a link here. Remember, this is all about mutual support and accountability! Chris has also made this charming icon that you are welcome to use on your blog, if you’d like. Sciwrite logo, by Chris Rowan

So, how’s it going? Are we making progress?
Continue reading

Categories: academic life, by Anne

Stuff we linked to on Twitter last week

A post by Chris RowanA post by Anne JeffersonAnne has an article in this week’s Eos about the conference she went to in the Galapagos this summer. It is paywalled, annoyingly, but if you don’t have access and would like a copy of the article, let us know in the comments and we’ll email it out.

Other posts on All-geo

Earthquakes

Volcanoes

Tectonics

Fossils

(Paleo)climate

Water

Environmental

General Geology

Interesting Miscellaney

Categories: links

Scenic Saturday: Whitewater rafting in Charlotte, North Carolina.

A post by Anne JeffersonThis semester I am teaching a class on fluvial (river) processes that encompasses aspects of both hydrology and geomorphology. One of my goals is to take my students to as many of sizes and shapes of river as possible over the course of the semester. Usually, we go on one Saturday field trip that lets us experience a mountain river, but this year, scheduling conflicts made that virtually impossible. Instead, we took a lecture + lab period, stayed a little closer to home, and viscerally experienced a totally unnnatural mountain river at the US National Whitewater Center.

First view of the whitewater channel, photo by A. Jefferson

First view of the whitewater channel. Downstream of the bridge, note the supercritical flow, hydraulic jump, and downstream standing waves. These are features of mountain channels not frequently seen in lowland streams.

Basically, the whitewater contains two channels filled with rapids that empty into a big pool. Water is pumped from the pool at the bottom back up to the pool at the top and the raft (and the people on the raft) get pulled back to the top on a big conveyor belt. When no one is rafting or kayaking, the pumps are turned off and all of the water drains to the bottom pool. You can see that lower pool in the background of the top photo.

Going down the channel there’s a series of rapids that look something like this. Sometimes bigger, sometimes tighter, and sometimes at a curvy point in the channel.

Hydraulic jump at the USNWC (photo by A. Jefferson)

The smooth tongue of water pouring over the drop just to the left of the channel centerline is supercritical flow, and the whitewater at the base is the hydraulic jump where flow becomes subcritical again.

The facility was built for a mix of casual visitors who pay for a guide to take them on a 90 minute raft ride and serious kayakers training for international competition. The Olympic whitewater kayaking trials were held here in 2008. The poles hanging from wires in the photos above can be moved around to set different courses for the kayakers. So the channel was designed to allow each rapid to run in ways ranging from mildly exciting to likely to catapult you out of your raft.

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Looking up the channel.There are multiple lines to run in these rapids, some harder than others

The guides do a good job of tailoring the experience to the level desired by the people in their raft. Our group divided into two raft. One filled with students who wanted to go wild, and they did, all ending up out of the raft at least once during the trip. Most of the students in the other raft had never been on whitewater before so decided to start a bit milder, but we still had our excitement by the end. And I don’t think I’ll ever forget the look on my grad student’s face as she tried to haul me back into raft after I got thrown out surfing a rapid and came up on the other side of the boat. I think she was far more terrified than I was – she might need a new thesis advisor!

After our raft trip was over we had some time to explore the other adventures to be had at the Whitewater Center. There’s flatwater kayaking, mountain biking, climbing walls, ziplines, and places just to relax and watch the water. I took the following video of some other rafters going down the rapids pictured above. I’ll note that they all seem to manage to stay in their boats.

Fun! With a side dose of education. That sentiment seems to be the consensus on the student evaluations I gave out last week — the whitewater trip has been a highlight of the semester.

Categories: by Anne, geomorphology, hydrology, science education

A writing challenge

A post by Anne JeffersonAre you up for a challenge? A writing challenge? A friendly, mutually-supportive writing challenge?*

I need to write some papers. My tenure portfolio goes out for review in May, and I want to get a couple more papers into review before then. Reviewers willing, I’d love to have another paper in two in press before May. The ticking of the biological clock ain’t got nothing on the ticking of the tenure clock, and journal articles are a major metric by which my academic success will be measured.

I know I’m not the only one sitting on some data that needs to become a paper or a great idea that needs to become a proposal. (If you’re not an academic, I bet you still have some piece of writing you know you should do.) And I know I’m not the only one who would benefit from having a group of friends provide some supportive encouragement, but also accountability. That’s why I’m setting myself a challenge, and I’m inviting you all to join in.

My goal is to get a manuscript into review by the time I arrive at AGU on Sunday the 4th of December. The data are in place and a few sections are written, but I need to do a bunch of writing, get the figures and tables into publication-quality shape, and get my co-author (and former graduate student) to agree it’s ready to go out. That’s a substantial project for the next 5 weeks (especially on top of an otherwise busy schedule), but I think it’s doable. More importantly, I need to do it. And I could use your help.

Here’s the plan. Use the comments below to tell me what you want to accomplish in the next 5 weeks. Each Sunday evening, I’ll stick up a post summarizing what I’ve accomplished during the past week, and what I need to get done in the next week order to reach my goal. You can do the same in the comments or on your own blog (with a link in the comments here, please!) During the week, we can use whatever means we please, such as reviving Brian Roman’s old #sciwrite tag on Twitter, to keep in touch, provide encoruagement, and brag about our progress. By December 4th, we will have reached our goals and we can go out for a virtual or real celebratory drink. Maybe I’ll even come up with some sort of prize or badge to reward participation.

The point of this challenge is to collectively focus on the important task of writing up our fantastic ideas and data, share them with our fellow scientists and the world, and make ourselves happier and less anxious in the process. So let’s get writing….first in the comments below to share your goal and plan, and then in the languishing word processor document that contains the seeds of your masterpiece.

*Yes, the timing and spirit of this challenge borrows heavily from InaDWrimo and NaNoWriMo. If there will be a broader InaDWriMo group this year, please let me know. Otherwise, all disciplines and non-academics are welcome to participate here.

Categories: academic life, publication