How do we know if an earthquake is tectonic or anthropogenic?

•15 June 2013 • 1 Comment

As I scroll through memories to file them away in the limited catalog that is my brain, I’m reminded of a question I once posed during a seminar presentation. The presentation was by one of the research committee members that was commissioned by the U.S. Department of Energy to study human-induced seismicity, done in June 2012. When the presentation concluded finished, I asked, “Did the committee ever investigate anything else [other than human activities related to oil and gas extraction] that might be causing the recent activities in the midwest?” A faculty member stepped-in to declare that they are submitting a paper correlating mid-continent seismicity to oil and gas extraction; which, still didn’t answer my question. If the answer to my question is “No, we only seek to determine whether earthquakes are human-induced, and not ask what else could be causing a deviation in what we think is normal seismicity.” then this is (to me) a non-scientific approach — post a comment below as I would love to hear your thoughts on this.

This post is merely a philosophical question that is spawned from that unanswered question.

Mind you, I am not asking how we can tie earthquakes to oil and gas. We know that. We know that either pumping fluids in or out of the ground, the pressure around the rocks change. Some may strengthen the fault (making it less likely to slip or develop a new fault) and some may weaken the fault (making it more likely to slip or develop a new fault). The first known case of the latter is well-documented, when Rangley, Colorado suddenly became seismically active in the 1960’s. Since then, there have been about a dozen cases in the U.S. that clearly document human involvement in earthquake triggering. There have been numerous more intraplate earthquakes that are not (or not yet, if you wish) tied to human activities, and are deemed tectonic. We try to fit these earthquakes into a model where humans are implicated, if that doesn’t fit, then it must be the other — so what’s the big deal?

The big deal is that determining whether earthquakes are caused by human activity is socially biased and politically charged. When the ground rumbles and buildings start to wiggle, we want to know where to point the proverbial finger of blame. When, in most cases, the finger points to nature, media outlets and politicians can’t really stir it to a frenzy. Really, what can people do other than move somewhere else that’s not earthquake-prone. Now, if the finger points to man (or corporations), people tend to get excited about tarring and feathering the culprit. Some seismologists say, mid-continent earthquakes are definitely anthropogenic. Some seismologists say, only a handful of earthquakes are human-induced and that they might be aftershocks from previous large earthquakes. Keep in mind that these people are working with the same data! Identical observations, different hypotheses.

When the New Madrid earthquakes happened in the early 1800’s, nobody claimed foul on fracking and no politician placed an embargo on oil and gas industries (probably because they didn’t exist yet). If the New Madrid earthquakes were to happen in present time, how are we (scientists, the public, media, etc.) going to view them?

What happens when you ASS U ME?

•27 March 2013 • Leave a Comment

Keranen et al., 2013

After reading a recent study paper that links large (≥ Mw 5.0) earthquakes in Oklahoma to wastewater disposal, I am left with the dissatisfied feeling that the title and media buzz surrounding the paper’s release is a bit over-sensationalized.

The paper is a solid piece of seismology that locates three major events with hundreds of aftershocks — if only the story ended there (then it probably wouldn’t have gotten into Geology). Where it falters scientifically is the supposition that these events are “linked” to wastewater injection wells. The only link, that is clear, is that theses earthquakes occurred near the injection wells. The authors cite well-documented studies that have data, which correlate seismicity with fluid injection. This paper on the other hand, did not have any such data. What it does have is a lot of suppositions and cartoon diagrams of what could be happening.

The physics of induced seismicity is well established, from laboratory beer can experiments, to field studies in Rangely, CO and Dallas-Forth Worth, TX. We know how earthquakes are triggered. What we don’t know is if the Oklahoma earthquakes are indeed triggered events — in my humble seismologic opinion, this question is still unanswered. The authors did not sufficiently present data to validate this claim:

Here we present a potential case of fluid injection into isolated pockets resulting in seismicity delayed by nearly 20 yr from the initiation of injection, and by 5 yr following the most substantial increase in wellhead pressure. — Keranen et al., 2013 (Geology)

There are other ways to induce seismicity in the midcontinent. Let us discount those other ways first, then we can make educated hypotheses as to what else could be causing these intraplate earthquakes. When we, as scientists, seek to prove our assumptions without considering other explanations, the end result is damning to the community as a whole.

Disclosures:
(1) As a seismologist, I would be scientifically thrilled to induced and study large (≥ Mw 8.0) in the field. Unfortunately, I do not see (in the data) that these moderate earthquakes in Oklahoma are indeed induced.
(2) I am neither for nor against oil companies and their drilling practices. It is what it is.
(3) I am against inconclusive studies that mislead other scientists and the general public with sensationalism and unfounded assumptions. That’s just wrong.
(4) I have tremendous respect for the authors of this paper as scientists, I just think the conclusion is a bit unpolished. The study requires a more thorough treatment in a longer publication.
(5) Everything here is my own opinion.

Blogroll for CPSGG Intro to Field 2013

•1 February 2013 • Leave a Comment

Geology: an engineer’s approach

Between A Rock and A Cactus

Brunton Times

Stratification Superstar

OU Field Geology

Hot Rocks and Other Cool Geology Stuff

bakereful

sdraper26

Little prince’s adventure

linhvo91

The Paradigm of a Spherical Earth

geology, don’t take it for granite

knottsj5953

The Rug that Tied the Room Together

Where is Intro to Field Going?

•1 February 2013 • 14 Comments

Screen shot 2013-02-01 at 3.29.30 PM

 

We are headed to Lee’s Ferry, AZ for Spring Break (Mar. 16-24). This is a list of student process blogs that will talk about research ideas that will be conducted during our fieldtrip.

A new piece of the earthquake puzzle

•5 October 2012 • 1 Comment

A paper, in the journal Science, comes out today, which presents new data and insight on earthquake physics*. Numerous experiments have been conducted by researchers all over the globe to approximate the physical conditions (lithology, pressure, temperature, etc.) where earthquakes occur. This paper presents a new type of experiment, which they call “Earthquake-Like Slip Events” (or ELSE experiments). So, what makes this procedure different? A short summary on the paper was already written, so I will not bother repeating it. I just wanted to elaborate on an aspect of ELSE that is pretty awesome.

Traditional rock mechanics experiments, in essence, slide rocks against each other, and (commonly) driven by a servo or electric motor — the rocks will slide at a prescribed velocity, for a given time, to reach a predetermined distance. Experimenters then extract valuable data about the sliding behavior (e.g., friction, heat, wear) of those rocks. The energy for these experiments are practically infinite; meaning, as long as you have electricity, the motor will drive the rocks as fast or long as you told them to go.

The ELSE experimental approach differs, in that a massive (5 ft. diameter, and 500 lbs.) flywheel stores rotational energy, then unleashed that energy to a pair of rock-discs. No additional power is supplied to the system when the flywheel and rocks are engaged. The rock determines how the fast it’s going to slip, and how long it will slip — not a motor. A visual aid would be like revving your engine at a stop sign, then popping the clutch to induce a burn out, or you can also watch the video below.

The finite energy approach might be a better approximation for how a large-magnitude earthquake slips, since the earthquake cycle consists of energy build-up and release**. And as far as I know, this machine is the first of its kind, but do give a comment below if you know of another!

                                  

* It is my opinion that the physics of earthquakes is somewhat of a beast — if you would like to form your own opinion, a “summary” on the topic can be read here [PDF].

** Note that I may be biased, since I am one of the authors of the paper.

A glimpse of earthquake fracture mechanics

•19 February 2012 • Leave a Comment

A small group of rotary shear friction investigators in earthquake physics (from the U.S., Italy, Japan, and China) had a collaborative meeting earlier last week, and I was luck enough to be a part of it. We openly exchanged ideas, and comments on where the community stands and what directions might be taken. Lots of good science and discussions. A lot of the discussions there were probably proprietary, so I won’t go into details. But, I was given permission to share this one:

In the meeting, Giulio Di Toro (one of the principal investigators in Italy) showed a video that needs to be seen — disintegrating marble (it’s as wicked as it sounds!). We (the University of Oklahoma group) have done this in dolomite, but we didn’t have high-speed footage.

The video is of Carrara marble, undergoing high-speed shearing (7 m/s) as recorded by a high-speed camera (4000 fps). The whole event, in real time, took place in less than 0.2 seconds.

UPDATE: For more rock mechanics fun. Check out my other post on the same machine, using different parameters, How To Make Homemade Lava.

My favorite geologic word: Anticlinorium

•24 June 2011 • 2 Comments

I don’t think it’s as obscure as geophantasmogram, but it’s not something you often hear around these parts, e.g., Oklahoma. Come to think of it, tectonics and topography don’t get mentioned much in local conversations either… But, I digress.

So, what is an anticlinorium? A more common geologic term that first comes to mind is anticline — and, as you may have guessed — the two are related. An anticlinorium is a series of anticlines (and synclines), which have also been anticlined. Wait, I know what you’re thinking, “Did he just use anticline as a verb?” Yes. Yes, I did. It’s the best one-line explanation I can think of. Another way to explain an anticlinorium is that of a fold with at least two considerably different, dominant wavelengths [ahem]. Forgive me. Sometimes, I speak geophysics.

For the best explanation, I suggest looking at a cross-section:

Why is this my favorite geologic word? Because geologists are wordsmiths, a lot of the words I use are somewhat made up (cf., anticlined) — this one is one of the more geologically valid ones. If anyone is interested, I’m in search of the ever elusive monoclinorium… Let me know if you see it first!

For a list of other geologists’ favorite words, check out the Accretionary Wedge #35.

 
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