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Stress Transfer Earthquakes

Stress Transfer Earthquakes. Andrei Popescu. What is Stress Transfer?. Post-seismic (and co-seismic) slip induced changes in the stress field surrounding an earthquake Can trigger other events (such as aftershocks) Influences both timing and slip distribution of subsequent events.

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Stress Transfer Earthquakes

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  1. Stress Transfer Earthquakes Andrei Popescu

  2. What is Stress Transfer? • Post-seismic (and co-seismic) slip induced changes in the stress field surrounding an earthquake • Can trigger other events (such as aftershocks) • Influences both timing and slip distribution of subsequent events

  3. Static Stress Changes vs. Dynamic Triggering • Static stress changes: changes in the stress field surrounding an earthquake associated with permanent fault offset from main rupture • Dynamic triggering: changes in stress field induced by the passage of large amplitude seismic waves from a separate (sometimes distant) event

  4. Effects of Stress Transfer • Short term: can trigger subsequent events (aftershocks are the best example of this). This is generally dependent on the conditions prior to the event (how close to failure was a certain area before the change in stress field) • Long term: can affect timing of subsequent events, bringing them either closer to failure, or farther from it • Slip distribution: extent of slip of a subsequent event can be altered by stress changes caused by the initial earthquake

  5. Proposed Theories • Coulomb Failure Stress • Viscoelasticity of upper mantle/lower crust • Pore fluid migration • Dynamic triggering • Aseismic creep

  6. Coulomb Failure Stress • CFS = |τ| + μ(σ + p) – S • |τ| = magnitude of shear stress • μ = coefficient of friction (constant) • σ = normal stress • p = pore fluid pressure • S = cohesion (constant)

  7. ΔCFS • ΔCFS = Δ|τ| + μ(Δσ + Δp) • If we assume a constant slip direction we get: • ΔCFS = Δτslip + μ(Δσ + Δp) • This equation is often simplified further: • ΔCFS = Δτslip + μ’Δσ • Where μ’ is a redefined “apparent” coefficient of friction which takes into account pore pressure • “This strategy is mostly and attempt to cover up our lack of knowledge about the role of pore fluids”

  8. ΔCFS and “Stress Shadows” • After an earthquake event, the entire surrounding stress field is subjected to changes which can be approximated using ΔCFS as detailed above • ΔCFS is resolved onto the fault plane and in the slip direction of the subsequent earthquake • ΔCFS > 0: the fault plane is loaded • ΔCFS < 0: the fault plane is relaxed (a stress shadow) • Stress shadows impose a time delay on subsequent events which can be approximated by calculating the amount of time needed for long-term tectonic loading to recover the induced ΔCFS

  9. North Anatolian Fault

  10. 1939 - 1992 • Ten M >= 6.7 events during this interval • Calculations of ΔCFS reveal that 9 out of 10 of the ruptures were brought closer to failure by the preceding ruptures • ΔCFS induced by these events is estimated to be equivalent to 3-30 years of secular stressing

  11. Results/Predictions • 9 out of 10 of the epicenters were located in areas where the preceding earthquakes had increased stress conditions • “We identify several faults with an heightened probability of failure. The port city of Izmit is most vulnerable to an earthquake on the Sapanca fault (Fig. 4g)…. We calculate a 30-yr probability during 1996-2026 for M>=6.7 shocks on the Geyve and Sapanca fault segments to be 12%; this probability is higher by a factor of 1.07 than the rate before the these segments were stressed by the 1967 earthquake.”

  12. 1999…

  13. References • Harris, Ruth A. 2000. Earthquake stress triggers, stress shadows, and seismic hazard. Current Science, Vol. 79, No. 9 • King, Geoffrey C.P., Stein, Ross S., Lin, Jian. 1994. Static stress changes and the triggering of earthquakes. Bulletin of the Seismological Society of America • Lin, Jian, Freed, Andrew M. 2004. Time-dependent viscoelastic stress transfer and earthquake triggering. Advances in Earth Sciences Monograph, Vol. 2, pp. 21-38 • Kane, Deborah L., Kilb, Debi, Berg, Arthur S., Martynov, Vladislav G., 2007. Quantifying the remote triggering capabilities of large earthquakes using data from the ANZA seismic network catalog (Southern California) • Stein, Ross S., Barka, Aykut A., Dietrich, James H. 1997. Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering. Geophysical Journal International, Vol. 128, pp. 594-604

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