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.

How much power in the Japanese tsunami of 2011? How much energy? Equivalent to how many nuclear bombs?

From Wiki

The Island of Honshu, Japan, is divided into five region, each of which contain sub-units called Prefectures.  The regions are: Chugoku, Kansai, Chubu, Kanto, and Tohoku. The two most northern ones are Tohoku (yellow) and Kanto (green).  The two cities that we have heard mentioned the most are Sendai and Tokyo, which lie in these two Prefectures, respectively.  The island of Honshu has a coastline of 5,450 km (3386 miles).

I am trying to estimate the magnitude of effort that it's going to take to remediate and help reconstruct Japan. Important: These numbers may change by factors of ten as new data and rigorous analyses come in, and they are not even internally consistent, but I think that it's important for the world to take notice now--while the spotlight is on--of the magnitude of the task faced by the Japanese, and us with them--to recover from this tragedy. I will revise these continuously as I get new input, and feedback from readers.

If you use the numbers below, please give credit to this site!

The power of a tsunami is a measure of energy per unit time. It was first defined back in the steam ages in order to compare steam engines to working draft horses. There's an excellent review of this history on Wiki under "horsepower." The power of a tsunami is the rate at which the kinetic energy in the tsunami is transferred to the shoreline.

If we follow the calculations of +Maths** and use data for Sri Lanka and the Sumatran earthquake, the power in a 1 meter high tsunami traveling at 200 m/s in the open ocean is about 1 megawatt per meter of shoreline, or 1 gigawatt per kilometer.  We simply do not have data, or even know, if the waves that hit the northern part of Japan were traveling at this speed; we do know from the videos being posted on the WWW that they were higher than 1 meter over long distances.  We don't know the exact amount of shoreline yet impacted on Honshu, but it appears that the northern Kanto and Tohoku provinces (yellow+green on the map above) were heavily hit on the Pacific side.  From the map, we can estimate that about half of the coastline is on the Pacific side (2725 km), and that about 1/2 of that coastline was hit (yellow+green+ a bit), about 1300 km. (Note made as new stories come in--this length of shoreline may be on the high end.)

This means that the power of the tsunami along that shoreline was about 1.3 *10^12, or 1.3 petawatts. To get energy, we need to know the duration of the tsunami. Let's estimate 100-1000 seconds. This means that the total energy was at least 1.3 * 10^14 joules, or 31 kilotons, almost equivalent to the 36 (15+21) kt that destroyed Hiroshima and Nagasaki, combined. If the duration was on the long end of these estimates, or the waves higher, this number could easily be 310 or even 3100 kilotons, equal to 10 or 100 Hiroshima's and Nagasaki's. My "gut feeling" from looking at the number of completely devastated cities is that these higher numbers are very likely.

The frequency and magnitude of these events is sobering--Haiti, Chile, New Zealand, Japan, with inevitable big earthquakes and tsunamis in Turkey (Istanbul) and the mideast, and Cascadia in the future.

Note added 3/13 at 2:45 CDT:  Summary of factors that would reduce the above estimates: velocity may be lower than 200 m/s, and total length of coastline now looks as if it's less than 1300 km. Summary of factors that would increase the above estimates: higher wave heights (reports from Sendai that the wave was as high as the trees, but I don't know what type of trees were in Sendai.

**Details of this estimate technique can be found at http://plus.maths.org/content/tsunami-1.