Coulomb stress transfer

Coulomb stress transfer is a seismic-related geological process of stress changes to surrounding material caused by local discrete deformation events.[1] Using mapped displacements of the Earth’s surface during earthquakes, computed Coulomb stress changes have suggested that stress relieved during an earthquake does not only dissipate, but can also move up and down fault segments, concentrating and promoting subsequent tremors.[2] Importantly, Coulomb stress changes have been applied to earthquake-forecasting models that have been used to assess potential hazards related to earthquake activity.[1][2][3][4][5]

Coulomb stress change

The Coulomb failure criterion requires that the Coulomb stress exceeds a value σf defined by the shear stress τB, normal stress σB, pore pressure p, and coefficient of friction μ of a failure plane, such that

σf = τB - μ(σB – p) [1]

It is also often assumed that changes in pore fluid pressure induced by in changes stress are proportional to the normal stress change across the fault plane.[6] These effects are incorporated into an effective coefficient of friction μ’, such that

Δσf = ΔτB - μ’(ΔσB) [6]

This simplification allows for the calculation of Coulomb stress changes on a fault plane to be independent of the regional stress field but instead depends on the fault geometry, sense of slip, and coefficient of friction.

The significance of the Coulomb stress changes was discovered when mapped displacements of neighbouring fault movements were used to calculate Coulomb stress changes along faults. Results revealed that the stress relieved on faults during earthquakes did not simply dissipate, but also moved up and down fault segments. Moreover, mapped lobes of increased and decreased Coulomb stress around local faults exhibited increased and decreased rates of seismicity respectively shortly after neighboring earthquakes, but eventually return to their background rate over time.[7][8]

Earthquake stress triggering

Stress triggering describes the responsive rupturing of faults from increases in Coulomb stress caused by exogenous deformation events.[1] Although neighboring displacements often yield small magnitude stress changes, areas of disturbed Coulomb stress states have been successfully used to explain the spatial distribution of stress triggered aftershock seismicity.

On June 28, 1992, a M7.2 earthquake that struck near Landers, California was followed (about three hours later) by the M6.5 Big Bear foreshock earthquake 40 km away. Calculated Coulomb stress changes from both of these earthquakes showed a westward lobe of 2.1-2.9 bars of increased Coulomb stress to have resulted from the displacement associated with both earthquakes. Of the roughly 20,000 aftershocks that occurred 25 days after June 28 within a 5 km radius, more than 75% occurred in areas where Coulomb stress had increased and less than 25% occurred in areas where Coulomb stress had dropped.[1]

Another successful case study of earthquake prediction occurred along Turkey’s North Anatolian fault system. From 1939 to 1999, the Anatolian fault system had witnessed ten earthquakes of M6.6 or greater. The evolution of the Coulomb stress changes along the North Anatolian fault as a result of these earthquakes showed that 11 of the 13 ruptures occurred in areas of increased Coulomb stress caused by a previous rupture.[3][4] This method has been also used to predict seismicity around active volcanoes submitted to significant variation of stress in the magma chamber.[9]

Earthquake prediction

Main article: Earthquake prediction

Although no official Coulomb stress transfer prediction model is being used by government agencies, geologic surveys often analyze earthquake threats using Coulomb stress theory. As an example, the last of the previous thirteen earthquakes along Turkey’s North Anatolian Fault, near the town of Duzce, was successfully predicted by local geologists before the rupture occurred. This allowed for engineers to evacuate unstable structures and limit significant damage.[2] Scientists estimate that the probability of another earthquake along the Anatolian fault system is 62% over the next 30 years and will be located threateningly close to Istanbul.[3]

Examples of earthquake sequences

References

  1. 1 2 3 4 5 King, G.C.P.; Stein, R.S.; Lin, J. (1994). "Static stress changes and the triggering of earthquakes". Bulletin of the Seismological Society of America 84 (3): 935–953.
  2. 1 2 3 Stein, R.S. (2003). "Earthquake Conversations". Scientific American 288 (1): 72–79. doi:10.1038/scientificamerican0103-72.
  3. 1 2 3 Stein, R.S.; Barka, A.A.; Dieterich, J.H. (1997). "Progressive failure on the north Anatolian fault since 1939 by earthquake stress triggering". Geophysical Journal International 128: 594–604. Bibcode:1997GeoJI.128..594S. doi:10.1111/j.1365-246x.1997.tb05321.x.
  4. 1 2 Barka, A.A.; Rockwell, T. K.; Reilinger, R.; Imren, C. (1999). "Kinematics of the central marmara sea ridges". EOS, Transactions, American Geophysical Union 80 (46): 664.
  5. ↑ Parsons, T.E.; Dreger, D.S. (2000). "Static-stress impact of the 1992 landers earthquake sequence on nucleation and slip at the site of the 1999 M = 7.1 hector mine earthquake, southern California". Geophysical Research Letters 27 (13): 1949–1952. Bibcode:2000GeoRL..27.1949P. doi:10.1029/1999gl011272.
  6. 1 2 Beeler, N.M.; Simpson, R. W., J.; Hickman, S. H.; Lockner, D. A. (2000). "Pore fluid pressure, apparent friction, and coulomb failure". Journal of Geophysical Research 105 (25): 542. Bibcode:2000JGR...10525533B. doi:10.1029/2000JB900119.
  7. ↑ Dieterick, J.H.; Kilgore, B.D. (1994). "Direct observation of frictional contacts; new insights for state-dependent properties". Pure and Applied Geophysics 143 (1-3): 283–302. Bibcode:1994PApGe.143..283D. doi:10.1007/bf00874332.
  8. ↑ Toda, S.; Stein, R.S. (2003). "Toggling of seismicity by the 1997 Kagoshima earthquake couplet; a demonstration of time-dependent stress transfer". Journal of Geophysical Research 108: 12. Bibcode:2003JGRB..108.2567T. doi:10.1029/2003jb002527.
  9. ↑ J.Gargani, L.Geoffroy., S.Gac, S.Cravoisier (2006). "Fault slip and Coulomb stress variations around a pressured magma reservoir : consequences on seismicity and magma intrusion". Terra Nova 18: 403–411. doi:10.1111/j.1365-3121.2006.00705.x.
  10. ↑ Zhang, Q.; Zhang P.; Wang C.; Wang Y.; Ellis M.A. (2003). "Earthquake triggering and delaying caused by fault interaction on Xianshuihe fault belt, southwestern China". Acta Seismologica Sinica 16 (2): 156–165. Bibcode:2003AcSSn..16..156Z. doi:10.1007/s11589-003-0018-5.

External links

This article is issued from Wikipedia - version of the Friday, April 01, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.