Options

Earthquakes

Here's a preview of a new book on earthquakes and earthquake prediction:

Comments

  • 1.
    edited September 24

    And this is a good survey paper on tsunami detection and how it relates to tidal prediction.

    S. Consoli, D. R. Recupero, and V. Zavarella, “A survey on tidal analysis and forecasting methods for Tsunami detection,” J. Tsunami Soc. Int. 33 (1), 1–56.

    The question is whether we can one use knowledge of tides to deconvolute a tsunami signal from the underlying tidal signal.

    This paper cites the one above

    Percival, Donald B., et al. "Detiding DART® buoy data for real-time extraction of source coefficients for operational tsunami forecasting." Pure and Applied Geophysics 172.6 (2015): 1653-1678.

    This is what the raw buoy signal looks like, with the tsunami at the end:

    After removing the tidal signals, the isolated tsunami impulse response (due to the 2011 Japan quake) looks like:

    Comment Source:And this is a good survey paper on tsunami detection and how it relates to tidal prediction. S. Consoli, D. R. Recupero, and V. Zavarella, [“A survey on tidal analysis and forecasting methods for Tsunami detection,”](https://t.co/99oJArTzdo) J. Tsunami Soc. Int. 33 (1), 1–56. The question is whether we can one use knowledge of tides to deconvolute a tsunami signal from the underlying tidal signal. This paper cites the one above Percival, Donald B., et al. ["Detiding DART® buoy data for real-time extraction of source coefficients for operational tsunami forecasting."](https://arxiv.org/pdf/1403.0528) Pure and Applied Geophysics 172.6 (2015): 1653-1678. This is what the raw buoy signal looks like, with the tsunami at the end: ![](http://imageshack.com/a/img923/8262/HxJK3w.png) After removing the tidal signals, the isolated tsunami impulse response (due to the 2011 Japan quake) looks like: ![](http://imageshack.com/a/img924/2434/knQssD.png)
  • 2.

    The above analysis was done with 6 constituent tidal parameters.

    I have a home grown spreadsheet that uses a solver plugin that can fit to these tidal patterns.

    This is one I did on the same waveform (after digitizing the plot) with 4 major tidal parameters and 4 minor parameters:

    q

    The yellow region is training which reached almost a 0.99 correlation coefficient, with the validation region reaching 0.92

    This is the complex Fourier spectrum:

    qf

    I've been wanting to try this for awhile -- to see if the solver setup that I've been using for fitting to ENSO would work for conventional tidal analysis.

    Sure enough, if you give it the recommended tidal parameters, the solver will grind away and eventually find the best fitting amplitudes and phases for each parameter.

    That's how easy it is to do tsumani detection from buoy data; have about 15 days worth of leading tidal buoy data and continuously update it, comparing it to a model and look for any discrepancies in the sea-level height.

    Comment Source:The above analysis was done with 6 constituent tidal parameters. I have a home grown spreadsheet that uses a solver plugin that can fit to these tidal patterns. This is one I did on the same waveform (after digitizing the plot) with 4 major tidal parameters and 4 minor parameters: ![q](http://imageshack.com/a/img923/7308/kqLPyD.png) The yellow region is training which reached almost a 0.99 correlation coefficient, with the validation region reaching 0.92 This is the complex Fourier spectrum: ![qf](http://imageshack.com/a/img924/5681/95yDo3.png) I've been wanting to try this for awhile -- to see if the solver setup that I've been using for fitting to ENSO would work for conventional tidal analysis. Sure enough, if you give it the recommended tidal parameters, the solver will grind away and eventually find the best fitting amplitudes and phases for each parameter. That's how easy it is to do tsumani detection from buoy data; have about 15 days worth of leading tidal buoy data and continuously update it, comparing it to a model and look for any discrepancies in the sea-level height.
  • 3.

    The wikipedia page gives references for the terms of the predictability debate.

    https://en.m.wikipedia.org/wiki/Earthquake_prediction#1990:New_Madrid.2C_U.S..28Browning.29
    

    "Despite the confident announcement four decades ago that seismology was "on the verge" of making reliable predictions,[247] there may yet be an underestimation of the difficulties. As early as 1978 it was reported that earthquake rupture might be complicated by "heterogeneous distribution of mechanical properties along the fault",[248] and in 1986 that geometrical irregularities in the fault surface "appear to exert major controls on the starting and stopping of ruptures".[249] Another study attributed significant differences in fault behavior to the maturity of the fault.[250] These kinds of complexities are not reflected in current prediction methods.[251]

    Seismology may even yet lack an adequate grasp of its most central concept, elastic rebound theory. A simulation that explored assumptions regarding the distribution of slip found results "not in agreement with the classical view of the elastic rebound theory". (This was attributed to details of fault heterogeneity not accounted for in the theory.[252])

    Earthquake prediction may be intrinsically impossible. It has been argued that the Earth is in a state of self-organized criticality "where any small earthquake has some probability of cascading into a large event".[253] It has also been argued on decision-theoretic grounds that "prediction of major earthquakes is, in any practical sense, impossible."[254]

    That earthquake prediction might be intrinsically impossible has been strongly disputed[255] But the best disproof of impossibility – effective earthquake prediction – has yet to be demonstrated.[256]"

    I had to dig out working links to the refs.

    [253] Geller, Robert J.; Jackson, David D.; Kagan, Yan Y.; Mulargia, Francesco (14 March 1997), "Earthquakes Cannot Be Predicted", Science, 275 (5306): 1616, doi:10.1126/science.275.5306.1616.

    [254] Matthews, Robert A. J. (December 1997), "Decision-theoretic limits on earthquake prediction", Geophysical Journal International, 131 (3): 526–529, Bibcode:1997GeoJI.131..526M, doi:10.1111/j.1365-246X.1997.tb06596.x.](http://web.csulb.edu/~rodrigue/quake/geller.html).

    [255] Sykes, Lynn R.; Shaw, Bruce E.; Scholz, Christopher H. (1999), "Rethinking Earthquake Prediction" Pure and Applied Geophysics, 155 (2–4): 207–232, Bibcode:1999PApGe.155..207S, doi:10.1007/s000240050263.

    [255] Evison, Frank (October 1999), "On the existence of earthquake precursors", Annali di Geofisica, 42 (5): 763–770.

    Comment Source:The wikipedia page gives references for the terms of the predictability debate. https://en.m.wikipedia.org/wiki/Earthquake_prediction#1990:New_Madrid.2C_U.S..28Browning.29 "Despite the confident announcement four decades ago that seismology was "on the verge" of making reliable predictions,[247] there may yet be an underestimation of the difficulties. As early as 1978 it was reported that earthquake rupture might be complicated by "heterogeneous distribution of mechanical properties along the fault",[248] and in 1986 that geometrical irregularities in the fault surface "appear to exert major controls on the starting and stopping of ruptures".[249] Another study attributed significant differences in fault behavior to the maturity of the fault.[250] These kinds of complexities are not reflected in current prediction methods.[251] Seismology may even yet lack an adequate grasp of its most central concept, elastic rebound theory. A simulation that explored assumptions regarding the distribution of slip found results "not in agreement with the classical view of the elastic rebound theory". (This was attributed to details of fault heterogeneity not accounted for in the theory.[252]) Earthquake prediction may be intrinsically impossible. It has been argued that the Earth is in a state of self-organized criticality "where any small earthquake has some probability of cascading into a large event".[253] It has also been argued on decision-theoretic grounds that "prediction of major earthquakes is, in any practical sense, impossible."[254] That earthquake prediction might be intrinsically impossible has been strongly disputed[255] But the best disproof of impossibility – effective earthquake prediction – has yet to be demonstrated.[256]" I had to dig out working links to the refs. [253] Geller, Robert J.; Jackson, David D.; Kagan, Yan Y.; Mulargia, Francesco (14 March 1997), "Earthquakes Cannot Be Predicted", Science, 275 (5306): 1616, doi:10.1126/science.275.5306.1616. [254] Matthews, Robert A. J. (December 1997), "Decision-theoretic limits on earthquake prediction", Geophysical Journal International, 131 (3): 526–529, Bibcode:1997GeoJI.131..526M, doi:10.1111/j.1365-246X.1997.tb06596.x.](http://web.csulb.edu/~rodrigue/quake/geller.html). [255] Sykes, Lynn R.; Shaw, Bruce E.; Scholz, Christopher H. (1999), "Rethinking Earthquake Prediction" Pure and Applied Geophysics, 155 (2–4): 207–232, Bibcode:1999PApGe.155..207S, doi:10.1007/s000240050263. [255] Evison, Frank (October 1999), "On the existence of earthquake precursors", Annali di Geofisica, 42 (5): 763–770.
  • 4.

    I agree with the difficulty of predicting a single earthquake. But for an ensemble, the triggering point must be Boltzmann or Arrhenius-like with an associated activation energy. If a swept lunisolar forcing provides the extra delta in energy to trigger, that will be observed in the spatio-temporal statistics.

    Comment Source:I agree with the difficulty of predicting a single earthquake. But for an ensemble, the triggering point must be Boltzmann or Arrhenius-like with an associated activation energy. If a swept lunisolar forcing provides the extra delta in energy to trigger, that will be observed in the spatio-temporal statistics.
  • 5.

    "TULSA, Okla. (AP) — Oklahoma's former lead seismologist says he felt pressured by a University of Oklahoma official to not link the state's surge in earthquakes to oil and gas production."

    https://www.usnews.com/news/best-states/oklahoma/articles/2017-11-15/former-oklahoma-seismologist-testifies-in-earthquake-lawsuit

    "Holland also detailed a meeting that allegedly took place with Boren and Harold Hamm, a billionaire oilman who has given millions of dollars to the university. Holland said he was called into Boren's office after he wrote the paper.

    Holland said Boren "expressed to me that I had complete academic freedom, but that as part of being an employee of the state survey, I also have a need to listen to, you know, the people within the oil and gas industry."

    Holland testified that Hamm told him "to be careful of the way in which I say things, that hydraulic fracturing is critical to the state's economy in Oklahoma, and that me publicly stating that earthquakes can be caused by hydraulic fracturing was — you know, could be misleading, and that he was nervous about the war on fossil fuels at the time."

    Comment Source:> "TULSA, Okla. (AP) — Oklahoma's former lead seismologist says he felt pressured by a University of Oklahoma official to not link the state's surge in earthquakes to oil and gas production." https://www.usnews.com/news/best-states/oklahoma/articles/2017-11-15/former-oklahoma-seismologist-testifies-in-earthquake-lawsuit > "Holland also detailed a meeting that allegedly took place with Boren and Harold Hamm, a billionaire oilman who has given millions of dollars to the university. Holland said he was called into Boren's office after he wrote the paper. >Holland said Boren "expressed to me that I had complete academic freedom, but that as part of being an employee of the state survey, I also have a need to listen to, you know, the people within the oil and gas industry." >Holland testified that Hamm told him "to be careful of the way in which I say things, that hydraulic fracturing is critical to the state's economy in Oklahoma, and that me publicly stating that earthquakes can be caused by hydraulic fracturing was — you know, could be misleading, and that he was nervous about the war on fossil fuels at the time."
  • 6.
    edited November 23

    BBC R4 'Inside Science' reports on a study from the University of Colorado which claims that the frequencies of magnitude >7M earthquakes goes up with reduction of equatorial dimension correlating with millisecond differences in LOD.

    "What might the length of the day have to do with the likelihood of destructive earthquakes around the world? According to Professors Rebecca Bendick and Roger Bilham, there's a correlation between changes in the rate at which the Earth rotates and the incidence of earthquakes of Magnitude 7 and above. The rotation speed of the planet increases and decreases over periods of years and decades. From their research, the earth scientists say that there's an substantial increase in the number of powerful earthquakes around the world five years after the Earth attains a peak in its spin speed and enters a period of slow down. The difference in day length is tiny but it is enough, say the researchers, to trigger already stressed faults in the crust to move sooner than later."

    Comment Source:BBC R4 'Inside Science' reports on a study from the University of Colorado which claims that the frequencies of magnitude >7M earthquakes goes up with reduction of equatorial dimension correlating with millisecond differences in LOD. "What might the length of the day have to do with the likelihood of destructive earthquakes around the world? According to Professors Rebecca Bendick and Roger Bilham, there's a correlation between changes in the rate at which the Earth rotates and the incidence of earthquakes of Magnitude 7 and above. The rotation speed of the planet increases and decreases over periods of years and decades. From their research, the earth scientists say that there's an substantial increase in the number of powerful earthquakes around the world five years after the Earth attains a peak in its spin speed and enters a period of slow down. The difference in day length is tiny but it is enough, say the researchers, to trigger already stressed faults in the crust to move sooner than later." * http://www.bbc.co.uk/programmes/b09drjmh
  • 7.

    Interesting study. There are several timescales involved in LOD changes.

    The shortest time-scale is directly related to diurnal and semidiurnal lunisolar tides. This one also impacts earthquakes as per the recent USGS and Japan research

    The intermediate time-scale is empirically related to ENSO, but I think this transitively relates to lunar forcing, which is discussed over on the ENSO threads. In other words, lunar forces ENSO, which then contributes to the LOD changes.

    The longest time-scale is most puzzling to me, as the change is so gradual, but is thought to be due to mantle changes:

    Here they are on Chao's chart:

    lod

    That long one is the focus of the program

    Comment Source:Interesting study. There are several timescales involved in LOD changes. The shortest time-scale is directly related to diurnal and semidiurnal lunisolar tides. This one also impacts earthquakes as per the recent USGS and Japan research The intermediate time-scale is empirically related to ENSO, but I think this transitively relates to lunar forcing, which is discussed over on the ENSO threads. In other words, lunar forces ENSO, which then contributes to the LOD changes. The longest time-scale is most puzzling to me, as the change is so gradual, but is thought to be due to mantle changes: Here they are on Chao's chart: ![lod](https://i2.wp.com/imagizer.imageshack.us/a/img513/3263/ci3s.png) That long one is the focus of the program
  • 8.

    In the first alledged zoom out of this diagramm from a "Chao paper" (whatever you mean by that) the LOD changes in the range of 1 millisecond but in the first image in the range of 2 milliseconds.

    Comment Source:In the first alledged zoom out of this diagramm from a "Chao paper" (whatever you mean by that) the LOD changes in the range of 1 millisecond but in the first image in the range of 2 milliseconds.
  • 9.
    edited November 21

    I disagree. The longer term LOD variation was removed in in the inset, thus reducing the fluctuation extremes from 2 to 1. This is the paper by Chao cited in the figure: http://ivs.nict.go.jp/mirror/publications/gm2004/chao/

    Here is another from Chao, showing the wavelet decompostion of LOD signal

    wavelet

    B. F. Chao, W. Chung, Z. Shih, and Y. Hsieh, “Earth’s rotation variations: a wavelet analysis,” Terra Nova, vol. 26, no. 4, pp. 260–264, 2014.

    Comment Source:I disagree. The longer term LOD variation was removed in in the inset, thus reducing the fluctuation extremes from 2 to 1. This is the paper by Chao cited in the figure: http://ivs.nict.go.jp/mirror/publications/gm2004/chao/ Here is another from Chao, showing the wavelet decompostion of LOD signal ![wavelet](https://i2.wp.com/imageshack.com/a/img922/5931/dmd8IH.png) B. F. Chao, W. Chung, Z. Shih, and Y. Hsieh, “Earth’s rotation variations: a wavelet analysis,” Terra Nova, vol. 26, no. 4, pp. 260–264, 2014.
  • 10.
    nad
    edited November 22

    I disagree. The longer term LOD variation was removed in in the inset, thus reducing the fluctuation extremes from 2 to 1.

    OK on the image you showed it is not indicated that something had been taken away, the diagram header (Excess Length-of-day (LOD)) is exactly the same for the top as for the middle panel.

    In the paper you cited it is written:

    One sees that the interannul LOD variation is mainly caused by the anomalous mass transport (mostly in the east-west wind field) of the Southern Oscillation in the tropical Pacific-Indian Ocean.

    Here the author writes about interannual LOD but nothing indicates that data been taken away. It is in this paper: http://www.earth.sinica.edu.tw/~bfchao/publication/eng/2003-Chao-EOS-Geodesy is not just for static measurements any more.pdf

    where it is finally written:

    the blue curve is VLBI measurement, after removal of the seasonal terms due to mass transports of meteorological origin and tidal forces;

    So it is rather the short-term data (the annual) that had been taken away). Anyways do you know where he has the long-term LOD data from? The figure 1 caption just says:

    The blue curve is the entire ∆LOD data set that human kind ever acquired (the post-1960 densification of data resulted from the advent of the atomic clock);

    There is currently a discussion on https://plus.google.com/+TimothyGowers0/posts/GNdRfNqcZw9 about a paper, where nobody seems to know were the long-term LOD is coming from.

    Comment Source:> I disagree. The longer term LOD variation was removed in in the inset, thus reducing the fluctuation extremes from 2 to 1. OK on the image you showed it is not indicated that something had been taken away, the diagram header (Excess Length-of-day (LOD)) is exactly the same for the top as for the middle panel. In the paper you cited it is written: >One sees that the interannul LOD variation is mainly caused by the anomalous mass transport (mostly in the east-west wind field) of the Southern Oscillation in the tropical Pacific-Indian Ocean. Here the author writes about interannual LOD but nothing indicates that data been taken away. It is in this paper: http://www.earth.sinica.edu.tw/~bfchao/publication/eng/2003-Chao-EOS-Geodesy%20is%20not%20just%20for%20static%20measurements%20any%20more.pdf where it is finally written: >the blue curve is VLBI measurement, after removal of the seasonal terms due to mass transports of meteorological origin and tidal forces; So it is rather the short-term data (the annual) that had been taken away). Anyways do you know where he has the long-term LOD data from? The figure 1 caption just says: >The blue curve is the entire ∆LOD data set that human kind ever acquired (the post-1960 densification of data resulted from the advent of the atomic clock); There is currently a discussion on https://plus.google.com/+TimothyGowers0/posts/GNdRfNqcZw9 about a paper, where nobody seems to know were the long-term LOD is coming from.
  • 11.

    The long-term LOD seems to be the big mystery, and it also aligns to temperature variations.

    Dickey, J.O.; Marcus, S.L.; de Viron, O. Air temperature and anthropogenic forcing: Insights from the solid Earth. J. Clim. 2011, 24, 569–574. http://journals.ametsoc.org/doi/full/10.1175/2010JCLI3500.1

    There are some long tidal periodicities that may match according to this paper http://www.mdpi.com/2225-1154/5/4/83

    Comment Source:The long-term LOD seems to be the big mystery, and it also aligns to temperature variations. Dickey, J.O.; Marcus, S.L.; de Viron, O. Air temperature and anthropogenic forcing: Insights from the solid Earth. J. Clim. 2011, 24, 569–574. http://journals.ametsoc.org/doi/full/10.1175/2010JCLI3500.1 There are some long tidal periodicities that may match according to this paper http://www.mdpi.com/2225-1154/5/4/83
  • 12.

    The LOD plots at IERS start in 1992: https://data.iers.org/plottool/publicv2/2dLine.php?reset=true

    but I think they have measurements since around 1973/1974: https://datacenter.iers.org/eop/-/somos/5Rgv/plotname/7/FinalsAllIAU1980-LOD-BULA.jpg

    I doubt that tidal observations are so precise that you may reconstruct the LOD in milliseconds. It seems that there are some historical records on lunar occlusions or maybe other celestial observations, which are eventually combined with reconstructions of the earth magnetic field, but this seems not easy at least here

    "The evolution of the core-surface flow over the last seven thousands years" by I. Wardinski and M. Korte from 2008

    it is written:

    Recently, Dumberry and Bloxham [2006] sought time–dependent azimuthal flows from an archeomagnetic field model and compared the variations in the core angular momentum computed from these flow solutions to the observed variations deduced from records of historical solar and lunar eclipses [Stephenson and Morrison, 1995]. Their study shows that assumptions made to derive core angular momentum changes on a decadal timescale prove to be invalid for millennia.

    Where I sofar didnt manage to find out at what place in history they started to count in seconds and then in milliseconds.

    Comment Source: The LOD plots at IERS start in 1992: https://data.iers.org/plottool/publicv2/2dLine.php?reset=true but I think they have measurements since around 1973/1974: https://datacenter.iers.org/eop/-/somos/5Rgv/plotname/7/FinalsAllIAU1980-LOD-BULA.jpg I doubt that tidal observations are so precise that you may reconstruct the LOD in milliseconds. It seems that there are some historical records on lunar occlusions or maybe other celestial observations, which are eventually combined with reconstructions of the earth magnetic field, but this seems not easy at least here <a href="http://onlinelibrary.wiley.com/doi/10.1029/2007JB005024/pdf">"The evolution of the core-surface flow over the last seven thousands years"</a> by I. Wardinski and M. Korte from 2008 it is written: >Recently, Dumberry and Bloxham [2006] sought time–dependent azimuthal flows from an archeomagnetic field model and compared the variations in the core angular momentum computed from these flow solutions to the observed variations deduced from records of historical solar and lunar eclipses [Stephenson and Morrison, 1995]. Their study shows that assumptions made to derive core angular momentum changes on a decadal timescale prove to be invalid for millennia. Where I sofar didnt manage to find out at what place in history they started to count in seconds and then in milliseconds.
  • 13.

    Here is a plot from Chao from that same paper showing the contribution of LOD from various spectral sources. These are all defined by a characteristic frequency:

    chao

    Going from right to left

    1. Semi-diurnal tides --> Tidal forcing
    2. Diurnal tides --> Tidal forcing
    3. Long-period tides --> Tidal forcing
    4. 40-60 day oscillation --> (see below)
    5. Semi-annual --> Solar + Tidal
    6. Annual --> Solar + Tidal
    7. Core --> ???
    8. ENSO --> Tidal forcing
    9. QBO --> Tidal forcing
    10. Secular --> ???

    As for the 40-60 day oscillation, I was looking at my ENSO model with high resolution SOI data, and it appears to pick up this variation, with likely a slightly different response function than the longer period >1 year cycles that ENSO is known for.

    http://contextearth.com/2017/11/24/high-resolution-enso-modeling/

    soi

    The greater point in all this is that the vast majority of LOD variations is due to the cyclic variation in the lunisolar forcing. All these other behaviors such as ENSO and QBO that contribute to LOD variations are transitively related to lunisolar forcing as well.

    I actually don't know what would be so surprising about such a result, in that the forcing that is required to cause LOD changes likely comes from some external force, and there aren't that many forces to choose from.

    The only contribution remaining are from core changes in the mantle of the earth. I suppose that the earth's highly viscous mantle (with a liquid outer core that is much less viscous than the mantle) spinning at the rate that it does could also undergo changes that are ultimately tied to lunisolar tidal forcing.

    What's left are slight variations in the LOD due to earthquakes, which truly are noise, apart from the fact that even these are transitively related to triggering by lunar forcing.

    Comment Source:Here is a plot from Chao from that same paper showing the contribution of LOD from various spectral sources. These are all defined by a characteristic frequency: ![chao](https://i1.wp.com/ivs.nict.go.jp/mirror/publications/gm2004/chao/img3.gif) Going from right to left 1. Semi-diurnal tides --> Tidal forcing 2. Diurnal tides --> Tidal forcing 3. Long-period tides --> Tidal forcing 4. 40-60 day oscillation --> (see below) 5. Semi-annual --> Solar + Tidal 6. Annual --> Solar + Tidal 7. Core --> ??? 8. ENSO --> Tidal forcing 9. QBO --> Tidal forcing 10. Secular --> ??? As for the 40-60 day oscillation, I was looking at my ENSO model with high resolution SOI data, and it appears to pick up this variation, with likely a slightly different response function than the longer period >1 year cycles that ENSO is known for. http://contextearth.com/2017/11/24/high-resolution-enso-modeling/ ![soi](https://i0.wp.com/imageshack.com/a/img923/7154/PPfcVP.png) The greater point in all this is that the vast majority of LOD variations is due to the cyclic variation in the lunisolar forcing. All these other behaviors such as ENSO and QBO that contribute to LOD variations are transitively related to lunisolar forcing as well. I actually don't know what would be so surprising about such a result, in that the forcing that is required to cause LOD changes likely comes from some external force, and there aren't that many forces to choose from. The only contribution remaining are from core changes in the mantle of the earth. I suppose that the earth's highly viscous mantle (with a liquid outer core that is much less viscous than the mantle) spinning at the rate that it does could also undergo changes that are ultimately tied to lunisolar tidal forcing. What's left are slight variations in the LOD due to earthquakes, which truly are noise, apart from the fact that even these are transitively related to triggering by lunar forcing.
  • 14.

    http://arxiv.org/abs/1711.09898

    Initiation of Plate Tectonics on Exoplanets with Significant Tidal Stress

    J. J. Zanazzi, Amaury Triaud (Submitted on 27 Nov 2017) Plate tectonics is a geophysical process currently unique to Earth, has an important role in regulating the Earth's climate, and may be better understood by identifying rocky planets outside our solar system with tectonic activity. The key criterion for whether or not plate tectonics may occur on a terrestrial planet is if the stress on a planet's lithosphere from mantle convection may overcome the lithosphere's yield stress. Although many rocky exoplanets closely orbiting their host stars have been detected, all studies to date of plate tectonics on exoplanets have neglected tidal stresses in the planet's lithosphere. Modeling a rocky exoplanet as a constant density, homogeneous, incompressible sphere, we show the tidal stress from the host star acting on close-in planets may become comparable to the stress on the lithosphere from mantle convection. We also show that tidal stresses from planet-planet interactions are unlikely to be significant for plate tectonics, but may be strong enough to trigger Earthquakes. Our work may imply planets orbiting close to their host stars are more likely to experience plate tectonics, with implications for exoplanetary geophysics and habitability. We produce a list of detected rocky exoplanets under the most intense stresses. Atmospheric and topographic observations may confirm our predictions in the near future. Investigations of planets with significant tidal stress can not only lead to observable parameters linked to the presence of active plate tectonics, but may also be used as a tool to test theories on the main driving force behind tectonic activity.

    Comment Source:http://arxiv.org/abs/1711.09898 >Initiation of Plate Tectonics on Exoplanets with Significant Tidal Stress > >J. J. Zanazzi, Amaury Triaud >(Submitted on 27 Nov 2017) >Plate tectonics is a geophysical process currently unique to Earth, has an important role in regulating the Earth's climate, and may be better understood by identifying rocky planets outside our solar system with tectonic activity. The key criterion for whether or not plate tectonics may occur on a terrestrial planet is if the stress on a planet's lithosphere from mantle convection may overcome the lithosphere's yield stress. Although many rocky exoplanets closely orbiting their host stars have been detected, all studies to date of plate tectonics on exoplanets have neglected tidal stresses in the planet's lithosphere. Modeling a rocky exoplanet as a constant density, homogeneous, incompressible sphere, we show the tidal stress from the host star acting on close-in planets may become comparable to the stress on the lithosphere from mantle convection. We also show that tidal stresses from planet-planet interactions are unlikely to be significant for plate tectonics, but may be strong enough to trigger Earthquakes. Our work may imply planets orbiting close to their host stars are more likely to experience plate tectonics, with implications for exoplanetary geophysics and habitability. We produce a list of detected rocky exoplanets under the most intense stresses. Atmospheric and topographic observations may confirm our predictions in the near future. Investigations of planets with significant tidal stress can not only lead to observable parameters linked to the presence of active plate tectonics, but may also be used as a tool to test theories on the main driving force behind tectonic activity.
Sign In or Register to comment.