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Earth's Systems / Geological cycling / Plate tectonics and volcanism / Earth's heat engine, faulting, earthquakes and isostasy

Earth's heat engine, faulting, earthquakes and isostasy

How internal heat escaping through the surface drives slow mantle flow and plate motion, how plate motion loads faults that release strain in earthquakes or creep, how one earthquake triggers others, and how the mantle rebounds after ice unloading (isostasy).

Boundary: where this process starts

Starts with: Earth loses about 47 TW of internal heat through its surface (primordial cooling plus radioactive decay), the power supply for mantle convection

Boundary: where it ends

Ends after: Aseismic creep and slow slip on weakly coupled faults (about 30%, estimate); Most large earthquakes occur at subduction trenches; the 2011 Tohoku M9 released strain stored where the Pacific plate subducts beneath Japan

PARTICIPANTSRESOURCESFaultsMantleEarthquakesLithosphericplatesSubductingslabsGravitationalpotentialenergyInternal heatImpact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.70%Impact +2 of 5. Click for details and evidence.30%Impact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.↻ reinforces · weak · 0.1Impact 02 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Earth loses about 47 TW of internal heat through its surface (primordial cooling plus radioactive decay), the power supply for mantle convection: uses up Internal heatuses upPlate motion loads locked faults elastically; strain builds for decades to centuries until friction fails (elastic rebound): uses Gravitational potential energyHow a plate-boundary fault releases its strain: uses Gravitational potential energySudden earthquake slip on a strongly coupled fault (about 70%, estimate): uses Gravitational potential energyAseismic creep and slow slip on weakly coupled faults (about 30%, estimate): uses Gravitational potential energyEarthquake sizes follow the Gutenberg-Richter law: each magnitude step up is about ten times rarer; about 12,000-14,000 earthquakes are located each year: uses Gravitational potential energyMost large earthquakes occur at subduction trenches; the 2011 Tohoku M9 released strain stored where the Pacific plate subducts beneath Japan: uses Gravitational potential energyEach earthquake shifts stress on neighbouring faults: seismicity rises where stress increases (aftershocks decaying by Omori's law) and falls where it drops: uses Gravitational potential energyGlacial isostatic adjustment: the mantle flows back after ice unloading, lifting Hudson Bay about 10 mm/yr and sinking land south of the Great Lakes 1-2 mm/yr: uses Gravitational potential energyuses upInternal heat: uses upusesGravitational potential energy: usesusesGravitational potential energy: usesusesGravitational potential energy: usesusesGravitational potential energy: usesusesGravitational potential energy: usesusesGravitational potential energy: usesusesGravitational potential energy: usesusesGravitational potential energy: usesStart: Earth's heatengine, faulting,earthquakes a…STARTStart: Earth's heat engine, faulting, earthquakes and isostasyEnd: Earth's heatengine, faulting,earthquakes a…ENDEnd: Earth's heat engine, faulting, earthquakes and isostasyEarth loses about 47 TWof internal heatthrough its surfa…📄1 ↗1Earth loses about 47 TW of internal heat through its surface (primordial cooling plus radioactive decay), the power supply for mantle convectionPlate motion loadslocked faultselastically; stra…📄2Plate motion loads locked faults elastically; strain builds for decades to centuries until friction fails (elastic rebound)How a plate-boundaryfault releases itsstrain📄1How a plate-boundary fault releases its strainSudden earthquake slipon a strongly coupledfault (about 70…📄1Sudden earthquake slip on a strongly coupled fault (about 70%, estimate)Aseismic creep and slowslip on weakly coupledfaults (about 30…📄1Aseismic creep and slow slip on weakly coupled faults (about 30%, estimate)Earthquake sizes followthe Gutenberg-Richterlaw: each magnitu…📄2Earthquake sizes follow the Gutenberg-Richter law: each magnitude step up is about ten times rarer; about 12,000-14,000 earthquakes are located each yearMost large earthquakesoccur at subductiontrenches; the 20…📄1Most large earthquakes occur at subduction trenches; the 2011 Tohoku M9 released strain stored where the Pacific plate subducts beneath JapanEach earthquake shiftsstress on neighbouringfaults: seismici…📄3Each earthquake shifts stress on neighbouring faults: seismicity rises where stress increases (aftershocks decaying by Omori's law) and falls where it dropsGlacial isostaticadjustment: the mantleflows back after i…📄2 ↗1Glacial isostatic adjustment: the mantle flows back after ice unloading, lifting Hudson Bay about 10 mm/yr and sinking land south of the Great Lakes 1-2 mm/yr
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Earth loses about 47 TW of internal heat through its surface (primordial cooling plus radioactive decay), the power supply for mantle convection
MantleEarth's interiorInternal heat
Evidence (1) · added by Briangold-Claude
  • Davies & Davies 2010, Earth's surface heat flux, Solid Earth 1:5-24, https://se.copernicus.org/articles/1/5/2010/: The preferred estimate of Earth's surface heat flux is 47 +/- 2 TW, higher than previous estimates, from a global compilation with a correction for hot spots in young oceanic lithosphere. (confidence 0.9)
Plate motion loads locked faults elastically; strain builds for decades to centuries until friction fails (elastic rebound)
Lithospheric platesFaultsSubducting slabsGravitational potential energy
Evidence (2) · added by Briangold-Claude
  • Ozawa et al. 2011, Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake, Nature 475:373-376, https://doi.org/10.1038/nature10227: The strain accumulation rate at the Japan trench estimated from geodesy was much higher than the average strain released in previous interplate earthquakes, before the 2011 M9 event released it. (confidence 0.85)
  • Scholz & Campos 2012, The seismic coupling of subduction zones revisited, J. Geophys. Res. 117:B05310, https://doi.org/10.1029/2011JB009003: GPS measurements of upper-plate deformation during the interseismic period give geodetic estimates of how much of the plate convergence is locked (seismic coupling). (confidence 0.85)
⑂ How a plate-boundary fault releases its strain
FaultsSubducting slabsGravitational potential energy
Evidence (1) · added by Briangold-Claude
  • Scholz & Campos 2012, The seismic coupling of subduction zones revisited, J. Geophys. Res. 117:B05310, https://doi.org/10.1029/2011JB009003: Seismic coupling varies between and within subduction zones: high where normal forces are high, switching abruptly to low coupling below a critical normal force; the 70/30 split is an estimate. (confidence 0.6)
Sudden earthquake slip on a strongly coupled fault (about 70%, estimate)
FaultsEarthquakesGravitational potential energy
Evidence (1) · added by Briangold-Claude
  • Scholz & Campos 2012, The seismic coupling of subduction zones revisited, J. Geophys. Res. 117:B05310, https://doi.org/10.1029/2011JB009003: High coupling occurs for subduction zones under high normal force and asperities correlate with areas of high coupling. (confidence 0.7)
Aseismic creep and slow slip on weakly coupled faults (about 30%, estimate)
FaultsGravitational potential energy
Evidence (1) · added by Briangold-Claude
  • Scholz & Campos 2012, The seismic coupling of subduction zones revisited, J. Geophys. Res. 117:B05310, https://doi.org/10.1029/2011JB009003: Low coupling occurs fairly abruptly as the normal force falls below a critical value, with considerable variation within individual subduction zones. (confidence 0.7)
Earthquake sizes follow the Gutenberg-Richter law: each magnitude step up is about ten times rarer; about 12,000-14,000 earthquakes are located each year
EarthquakesFaultsGravitational potential energy
Evidence (2) · added by Briangold-Claude
  • Gutenberg & Richter 1944, Frequency of earthquakes in California, Bull. Seismol. Soc. Am. 34:185-188, https://doi.org/10.1785/BSSA0340040185: Gutenberg and Richter established the log-linear frequency-magnitude relation of earthquakes. (confidence 0.8)
  • IRIS (EarthScope) fact sheet, How often do earthquakes occur?, https://www.iris.edu/hq/inclass/fact-sheet/how_often_do_earthquakes_occur: The National Earthquake Information Center locates about 12,000-14,000 earthquakes each year; for each step up in magnitude earthquakes become much rarer and release about 32 times more energy. (confidence 0.8)
Most large earthquakes occur at subduction trenches; the 2011 Tohoku M9 released strain stored where the Pacific plate subducts beneath Japan
EarthquakesSubducting slabsPacific plateGravitational potential energy
Evidence (1) · added by Briangold-Claude
  • Ozawa et al. 2011, Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake, Nature 475:373-376, https://doi.org/10.1038/nature10227: Most large earthquakes occur along an oceanic trench where an oceanic plate subducts; magnitude-9 events are known from Chile, Alaska, Kamchatka, Sumatra and now Japan. (confidence 0.9)
Each earthquake shifts stress on neighbouring faults: seismicity rises where stress increases (aftershocks decaying by Omori's law) and falls where it drops
EarthquakesFaultsGravitational potential energy
Evidence (3) · added by Briangold-Claude
  • Stein 1999, The role of stress transfer in earthquake occurrence, Nature 402:605-609, https://www.nature.com/articles/45144: An earthquake alters shear and normal stress on surrounding faults; rates climb where stress increases (aftershocks) and fall where it drops, followed by time-dependent recovery. (confidence 0.9)
  • King, Stein & Lin 1994, Static stress changes and the triggering of earthquakes, Bull. Seismol. Soc. Am. 84:935-953, https://doi.org/10.1785/BSSA0840030935: Coulomb stress changes from the 1992 Landers earthquake explain the distribution of its aftershocks and the triggering of nearby events. (confidence 0.85)
  • Utsu, Ogata & Matsu'ura 1995, The centenary of the Omori formula for a decay law of aftershock activity, J. Phys. Earth 43:1-33, https://doi.org/10.4294/jpe1952.43.1: Aftershock rate decays with time after the mainshock following the Omori formula. (confidence 0.8)
Glacial isostatic adjustment: the mantle flows back after ice unloading, lifting Hudson Bay about 10 mm/yr and sinking land south of the Great Lakes 1-2 mm/yr
MantleLand surfaceIce sheetsGravitational potential energy
Evidence (2) · added by Briangold-Claude
  • Sella et al. 2007, Observation of glacial isostatic adjustment in stable North America with GPS, Geophys. Res. Lett. 34:L02306, https://doi.org/10.1029/2006GL027081: GPS shows present-day uplift of about 10 mm/yr near Hudson Bay, the site of thickest ice at the last glacial maximum, and subsidence of 1-2 mm/yr south of the Great Lakes. (confidence 0.9)
  • Peltier 2004, Global glacial isostasy and the surface of the ice-age Earth: the ICE-5G (VM2) model and GRACE, Annu. Rev. Earth Planet. Sci. 32:111-149, https://doi.org/10.1146/annurev.earth.32.082503.144359: The viscoelastic response of the solid Earth to changing ice loads (ICE-5G/VM2) is constrained by relative sea-level and gravity observations. (confidence 0.85)