Links between earthquakes and other geologic activity

Nature Geoscience (August volume 6(8), pp. 585-672) has a fairly long section ("a Web Focus") and a number of papers on geologic activity associated with or triggered by earthquakes. The introductory editorial reflects that in 1835 Charles Darwin voyaging on the Beagle experienced a large earthquake near Concepcion, Chile, and noted that within the hour a train of volcanoes in the Andes spouted out a dark column of smoke (though it would take a journey into Darwin's notes to determine whether he thought this was volcanic gas or perhaps debris from landslides. The implication in the editorial is that it was the former).
   

Illustration of the elastic rebound part of volcanic arc
subsidence after a megathrust earthquake

The first paper in this section (by Sigurjon Jonsson) summarizes the deflation of volcanic areas in response to the 2011 Tohoku and 2010 Maule (Chile) earthquakes. Both settings are at subduction zones (see figure), and the volcanoes that subsided were on the overriding plate. Prior to the earthquake, strain accumulates and compresses the overriding plate. During and after the earthquake, the overriding plate extends and subsides. However, subsidence beyond that which can be explained by this process is observed.
     In the case of the Tohoku earthquake, Takada and Fukushima documented 5-15 cm of subsidence at a distance of 150-200 km from the rupture earthquake, but no volcanic eruptions. They suggest that subsidence is caused by sinking of magma reservoirs and their warm host rocks through the colder surrounding crust. Prichard and colleagues noted that two earthquakes (1906, 1960) were followed by eruptions in the Andes within a year, but that no eruptions have been clearly associated with the 2010 earthquake. They were, however, able to document the 15 cm of subsidence, and suggest that hydrothermal fluids were released from hydrothermal systems surrounding the volcanoes in Chile during the 2010 quake, and that the escape of these fluids caused the volcanic areas to deflate.
     A second example of a proposed connection between earthquakes and geologic activity is more controversial: the Lusi mud volcano eruption. In 2006, mud erupted through and around a drill hole, flooding towns and displacing thousands of people.  Paul Davis summarizes a paper by Lupi et al. that proposes that the 2006 Lusi mud eruption in Indonesia (still continuing) was triggered by a M6.3 earthquake two days prior to the eruption and 275 km away.  Lupi et al. argue that strains, which are unarguably small at such a distance in homogeneous media,  were amplified by a downward concave layer of shale that acted as a parabolic reflector. Their simulations suggest that the stresses could have been about 100 kPa, five times higher than original estimates of 21 kPa. Such pressures, the assert, could have liquified the mud that resides at depth, resulting in the eruption of mud through the drill hole. This conclusion remains controversial (see discussion by R.J. Davies, et al., Earth and Planetary Science Letters, 272, 627-638, 2008).
     For a third example, Fischer et al. examine subduction zone earthquakes as triggers of submarine hydrocarbon seepage.  Offshore of Pakistan, the Arabian Plate subducts beneath the Eurasian plate. This is a region of intense seismicity, in particular a major earthquake (M8.1) occurred there in 1945. It occurred in an area where gas hydrates (methane clathrates) are present, and leakage of hydrocarbon gas is known to occur here. Methane and sulfates both occur in the ocean with sulfate being stable above about 5 mbsf, and methane at greater depths. The concentration of both goes to nearly zero at a depth known as the sulfate-methane transition (SMT). In a complicated chemical reaction, sulphate is consumed through anaerobic oxidation of methane (CH4 + SO24􏰀 ! HCO􏰀3 + HS􏰀 + H2O). Barium, being present in sea water, is precipitated at the SMT in so-called "barite fronts" and the abundance of barite can be used to reconstruct changes in upward methane flux.  The authors calculated that it would take approximately 38-91 years to produce the observed barite enrichments. This leads them to conclude that the barite production could have been initiated by the 1945 earthquake and an accompanying increase in methane flux due to release from the hydrates. If confirmed, submarine gas release triggered by earthquakes needs to be added to the list of processes that can add methane to the hydrosphere, and possibly to the atmosphere, in the carbon budget.




References: Takada, Y., and Fukushima, Y., Nature Geoscience, 6, 637-641, 2013.
Pritchard, M.E., Jay, J.A., Aron, F., Henderson, S.T., and Lara, L.E., Subsidence at southern Andes volcanoes induced by the 2010 Maule, Chile earthquake, Nature Geoscience, 6, 632-626, 2013.
Lupi, M., Saenger, E.H., Fuchs, F., and Miller, S.A., Lusi mud eruption triggered by geometric focusing of seismic waves, Nature Geoscience, 6, 642-646, 2013.
Fischer, D., et al., Subduction zone earthquake as potential trigger of submarine hydrocarbon seepage, Nature Geoscience, 6, 647-651, 2013.

Gansu, China, rain, mudslides, and now a shallow earthquake: are they related? And, was that shallow earthquake notice right?

A map showing the location of the December 16,
1920 M 7.8 earthquake
From Wiki here 

An alert has just come out over the USGS earthquake network that there was a very shallow (1 km depth) magnitude 5.9 earthquake in Gansu province, China, 13 km east of the city Chabu (or, later reported as 156 km west of Tianshui.). Interestingly, two other agencies give very different estimates of the magnitude and depth: a 6.3 at 10 km depth by GFZ (at the Helmholtz Centre in Potsdam) and a 6.1 at 15 km depth according to EMSC (the European Seismological Centre), as reported here. And, while I was checking this on the EMSC site the numbers changed before my eyes to a M6.0 at 10 km depth! It would have been interesting to see how this all sorts out--if the USGS depth of 1 km is correct, this is a very unusual earthquake, and I wonder if it is actually an event associated with a major landslide rather than a fault zone (this was the case on May 18, 1980 when the north flank of Mount St. Helens failed into a big landslide). However, when I checked into the USGS site here, the depth is now listed at 9.8 km.  Makes me wonder what that earlier bulletin was all about!

The epicenter appears to have been Dingxi City. Dingxi is a "prefecture level city" in the southeast of Gansu province. It's area covers 20,300 sq. km, and the population is reported as 2.7 million people (in 1 urban district, 6 counties, and 119 towns). It was an important city in early development of some of China's cultures because the Wei River, one of the Yellow River's biggest tributaries, flows here.  The surrounding terrain hills and ravines cut into the loess deposits, weak sandy deposits, possibly water-saturated from the recent rains. This does not bode well for damage.

 The earthquake occurred near midnight UTC on July 21. This follows, by only 8 days, a major landslide that reportedly trapped at least 100 tourists after a landslide cut off a road during a week of storms that have flooded rivers and triggered mudslides. At least 86 people were reported to have died by Chinese state media. Mudslides and floods are common in the mountainous areas of China, but this year seems to have been an especially bad one in many areas of Asia.

Map showing the relation of todays earthquake to
the major city of Tianshui.

In 2010, a deadly mudslide killed approximately 1500 people. After heavy rains, water built up behind a dam of debris that blocked a small river north of the city of Zhugqu. The dam broke, sending nearly 2 million cubic meters of mud and rocks through the town in a surge tens of feet high. A major problem in this area is that the forested areas have shrunk (by as much as 30% according to Wiki), and the reserve of timber has diminshed by 25% due to harvesting (these are 2010 numbers, and are relative to a base in the 1950's.) It is a region of massive construction of hydroelectric projects.

Gansu is also a region with many earthquakes.  In 1879, an earthquake with an estimated magnitude of 8.0 and Mercalli intensity XI (extreme) killed an estimated 220,000 people. This earthquake was preceded by foreshocks for a few days. The earthquake also triggered landslides that dammed local rivers up to 40-120 m.

Today's earthquake appears to be followed by numerous aftershocks, though it is difficult to tell where they are relative to the initial location given as 13 km east of Chabu. Some are reported at a distance of 156 km from Tianshui in Gansu province, a city of 3.5 million people.

A reader pointed out a site that covers earthquake preparedness here. Thanks!!

Heat Index vs. Humidex

From this site

It is, at the moment, 91 F in my former home town of Urbana, IL, the dew point is 75 F, the relative humidity is 59%, and the Heat Index is 102 F! In Toronto, Canada, it is 33.3 C (92 F) in  the humidity is 46%, the dew point is 67 degrees and the Humidex is 40 C (104 F). 

In contrast, where I live here near Seattle, the temperature is 73.7 F, and Weather Channel reports that "it feels like 77 F" (that's a jargon for the Heat Index.) The humidity is 57%, the dewpoint is 58 F.


What do these numbers mean, and how are they related to each other? First or all, a disclaimer: when I put those last numbers about temperature, dew point, and humidity into the NOAA government calculator that I cite below, I do not get the same answer as Weather Channel (77F); I get 74 F.  Either way, it's very comfortable here in the Pacific Northwest compared to conditions in the Midwest and eastern U.S. See below for further comments.

One difference is that Canadians use the Centigrade scale and we are stuck with the awkward Fahrenheit scale. However, it is possible to go back and forth between the two scales with some rounding off.  A simple way to interpret the Humidex is that it is equivalent to the dry temperature--that is, if the temperature is 30 C (86 F) and the calculated Humidex is 40 (104 F), then the humid heat "feels like" a dry temperature of 40 C (104 F).

The other differences are more complicated, and I have to say that--having lived in both countries--I had to laugh when I saw on Wiki that  "A joint committee formed by the United States and Canada to resolve differences has since been disbanded." Both scales use vapor pressure or dew point for the calculation, but the Canadians (perhaps because it is colder there?) use a dew point base of 45 F (7 C) for the humidex, whereas we Yanks use 57 F (14 C). The Heat Index, however, incorporates variables other than the vapor pressure, including 
The Heat Index formula is:


where the c's are constants, disputed by experts.

The Humidex formula is;


The Humidex is higher than the US Heat Index at a given temperature and humidity. A mathematical scientist looking at these two formulas would instantly wonder two things: it's amazing that they are even close to each other because of the difference in form, and they must apply over very restricted temeprature ranges because of the nonlinear dependence on R (relative humidity) and temperature (T).

In terms of discomfort, the above graphic illustrates the various levels of discomfort and danger on a Heat Index scale. Here are the rough rules used by Canadian weather forecasters for Humidex:

Less than 29°C, no discomfort
30°C-39°C, some discomfort
40°C-45°C, great discomfort
45°C-54°C, dangerous
Above 54°C, heat stroke imminent

Here's a national weather site that allows you to use either F or C, and either Dew Point temperature or relative humidity, to calculate the Heat Index. (The numbers will be slightly off because of rounding errors.) Here's a commercial site for calculating Humidex. Note that by the U.S. Heat Index chart, our Seattle conditions at 73.7 F aren't even worth putting on the chart! And, my guess is that the reason the calculators that I provide here give wierd answers for the Seattle situation is that the formulas just aren't very good at these "low" temperatures.

Do heat waves extend to outer space? And, EVA the space-flying cow.

Two members of the launch and recovery team
point to EVA the cow where she landed
in Death Valley. Photo from the
Facebook.com reference.

"Earth to Sky Calculus" is a group of middle and high school science enthusiasts based in Bishop, California. Since 2011 they have launched 30 balloons into the stratosphere, with 18 recording temperatures at the tropopause, the boundary between the tropopause and the stratosphere. They are hoping to do a satellite launch in 2013.
       Last month, when a heat wave swept across the U.S. Southwest, with temperatures in Death Valley reaching as high as 129 F, the students decided to find out if the heat wave extended all the way into space, that is, up into the stratosphere. On June 30, when it was 108 in Bishop, they launched a research balloon that had onboard a cryogenic thermometer and measured temperature up to 90,000 set. The thermometer registered a "low" temperature of -64.4 C, where the balloon passed through the tropopause. The troposphere is the coldest part of the atmosphere, and it was just as cold as usual on that day. Their measured temperatures ranged from about -68 C (-90 F) to -55C (-67 F).** The answer was: heat waves to not extend up to the tropopause.

A Google search about the Earth to Sky program reveals a video of  EVA the cow (from Tauranga, New Zealand) who, on April 22, 2013, they sent on a weather balloon to the edge of space. EVA successfully parachuted back into Death Valley. It took the students 18 hours to find her! This is a truly cool video!

The students have launched other items including a bobblehead of President Barack Obama on the day before Election Day in 2012. These kids look like they are having a lot of fun and learning a lot as well. Kudos to them, their families and teachers!

**This material from their Facebook page.

Tea leaves defy gravity, move upstream

Mate tea in a calabash gourd
Photo by Jorge Alfonso Hernandez
from Wiki

Water flows downstream, right? So, how can particles, such as tea leaves or chalk particles, floating on downstream-flowing water move upstream? This is a puzzle tackled by researchers recently. In work summarized in Science News here, Sebastian Bianchini describes how, one night when he was an undergraduate in 2008, he was making tea and noticed that by the time he had filled his cup containing tea leaves, some of the tea leaves had marched up into the pristine water in the kettle. In a sad comment on the difficulty of getting unusual work published, he and a physicist at the University of Havanna in Cuba, were unable to get their work published, even though it included some experiments.
    Last year, the duo met Troy Shinbrot, a physicist at Rutgers. Troy replicated the experiment, setting one tank of water 1 cm higher than another. The water flowed down an inclined channel, and into a waterfall 1 cm high.They added chalk and mate tea** to the bottom tank and observed the particles moving up to contaminate the upper tank. The flow is complicated in 3-D: the particles climb up the backside of the waterfall in a series of vortices, to the outside of the channel, and then can be transported back downwards through the center of the channel and over the front of the waterfall.

The experimental setup for the tea leaf experiment
Figure 1 in the referenced paper

     They hypothesized that the tea leaves in the lower tank disturbed the surface tension (bonds of hydrogens that create an elastic network at the surface) and that the particles moved up toward the pure water where the surface tension was higher, effectively climbing along the top of the water surface in defiance of gravity.
     The effect had been recognized earlier by physicists, but the magnitude had not been realized. In a simple back-of-the envelop analysis, the authors show that the surface tension difference between the lower (tea-contaminated) and upper (pure water) reservoirs is about 0.01 N m-1, and that the acceleration (for typical chalk particles) would be about 20 times gravity.
     To test the hypothesis that this is a surface tension effect, the authors dropped a liquid surfactant into the upper and lower reservoirs. When it was dropped into the upper reservoir, the contamination was abruptly eliminated, whereas when it was added to the lower reservoir, the contamination was initiated (if it had not already begun) or accelerated (if it was in progress.) In supplementary material, there are detailed 2-D simulations. There are many more experiments and quantitative analyses in the paper.
     Does this experiment have practical implications? The authors don't know yet, but are suspicious that particles might migrate upstream in a slow-moving river, or be able to sneak into the tips of laboratory pipettes, contaminating samples.

**Mate tea is a traditional South American tea made by infusing the leaves of yerba mate with hot water. The traditional way of brewing it is shown in the picture above.

Reference:

S. Bianchini et al. Upstream contamination by floating particles. Proceedings of the Royal Society A. July 3, 2013. doi: 10.1098/rspa.2013.0067.

M6.1 earthquake strikes Indonesia's Aceh province

     In 2004, an earthquake of estimated magnitude 9.1-9.3 off Aceh province in Indonesia triggered a tsunami that killed an estimated 230,000 people around the Pacific Rim in Asia. Today a much smaller, M6.1 struck, killing at least one person (possibly many more, news reports are still coming in), leaving two others missing, dozens injured, and several dozen homes damaged. The earthquake caused at least one landslide.

Map of Indonesia; the red square near Jakarta shows the
location of the 2012 M8.2 aftershock
From this site.
Today's M6.1 quake was at about 1:00 to the NE of the
epicenter of the 2004 quake (shown as the big
bull's eye on the left) in the center of the tip of
Sumatra.

     This is not the largest earthquake to hit Indonesia since the 2004 event; one quake, centered beneath the ocean floor and roughly 300 miles from Banda Aceh (the capital of Aceh province), was a M8.6. It was followed by a M8.2 aftershock. It is humbling to remember that a relatively small earthquake like today's M6.1 kills people, and would be major news if it occurred in the U.S. That people in Indonesia live with these killer quakes all of the time should not be forgotten.
    The 2004 event was located about 100 miles off the western coast of northern Sumatra at a depth of 19 miles below sea level (today's event was, in contrast, only about 6 miles deep and was centered below land; see map and caption). A huge section of length 810 miles ruptured during this quake. The main rupture was followed by secondary faulting (dubbed "pop up faults" on Wiki" that acted in concert with the main rupture to produce the massive tsunami that caused so much destruction around the Asian Pacific Rim. The total length of all of the faulting, which took place over several minutes, was about 1000 miles.