Doublet earthquake

Source: Wikipedia, the free encyclopedia.

In

Båth's law) and decrease in magnitude and frequency according to known laws.[4]

Doublet/multiplet events also have nearly identical seismic waveforms, as they come from the same rupture zone and stress field, whereas aftershocks, being peripheral to the main rupture, typically reflect more diverse circumstances of origin.[5] Multiplet events overlap in their focal fields (rupture zones), which can be up 100 kilometers across for magnitude 7.5 earthquakes.[6] Doublets have been distinguished from triggered earthquakes, where the energy of the seismic waves triggers a distant earthquake with a different rupture zone, although it has been suggested such a distinction reflects "imprecise taxonomy" more than any physical reality.[7]

Multiplet earthquakes are believed to result when asperities, such as large chunks of

elastic rebound theory), the initial multiplet quake only releases part of the pent-up stress when the rupture hits the asperity. This increases the stress across the asperity, which may fail within seconds, minutes, months, or even years.[8] In the 1997 Harnai earthquake the initial Mw 7.0 shock was followed by an Mw 6.8 shock just 19 seconds later.[9] The effect of such powerful shocks so close in time was to double the duration of ground shaking (bringing more structures to the point of collapse), and to double the area affected by the strongest shaking.[10] When a subsequent, and possibly stronger, shock comes hours or days later it may suffice to collapse structures weakened by the previous shock, with serious consequences to rescue and recovery efforts.[11]

Although there have been numerous earthquakes with two or even three primary shocks of such similar magnitude that picking one as the main shock can be somewhat arbitrary, it was not until the 1970s and 1980s that studies of

foreshocks and aftershocks.[12] Other studies have shown that about 20% of very large earthquakes (magnitude above 7.5) are doublets,[13] and that, in some cases, 37 to 75 percent of earthquakes are multiplets.[14] A theoretical study found about one earthquake in 15 (~7%) to be a doublet (using a narrow criterion of "doublet"),[15] but also found that in the Solomon Islands six of 57 M ≥ 6.0 earthquakes were doublets, and 4 of 15 M ≥ 7.0 earthquakes, showing that approximately 10% and 25% of those quakes were doublets.[16]

Doublet earthquakes pose a challenge to the

characteristic earthquake model used for estimating seismic hazard.[17] This model assumes that faults are segmented, limiting the extent of rupturing, and therefore the maximum size of an earthquake, to the length of the segment.[18] Newer forecasts of seismic hazard, such as UCERF3, factor in a greater likelihood of multisegment ruptures, which changes the relative frequency of different sizes of earthquakes.[19]

See also

Notes

  1. ^ Poupinet, Ellsworth & Frechet 1984, p. 5719.
  2. ^ Beroza, Cole & Ellsworth 1995, pp. 3977, 3978. Kagan & Jackson (1999, p. 1147) define doublets more precisely as "pairs of large earthquakes whose centroids are closer than their rupture size and whose interevent time is shorter than the recurrence time inferred from the plate motion.
  3. ^ Felzer, Abercrombie & Ekström 2004, p. 91.
  4. Omori's law, and Gutenberg–Richter law
    .
  5. ^ Poupinet, Ellsworth & Frechet 1984, p. 5719.
  6. ^ Kagan & Jackson 1999, p. 1147.
  7. ^ Hough & Jones 1997, p. 505.
  8. ^ Donner et al. 2015, p. 5.
  9. ^ Nissen et al. 2016, p. 330.
  10. ^ Nissen et al. 2016, p. 334.
  11. ^ Lin et al. 2008, pp. 593–594.
  12. ^ Oike 1971; Poupinet, Ellsworth & Frechet 1984.
  13. ^ Kagan & Jackson 1999, p. 1152.
  14. ^ Massin, Farrell & Smith 2013, p. 168.
  15. ^ Felzer, Abercrombie & Ekström 2004, p. 91.
  16. Kurile Islands
    .
  17. ^ Kagan & Jackson 1999, p. 1147; Nissen et al. 2016, p. 330.
  18. ^ Nissen et al. 2016, p. 334.
  19. ^ UCERF3 Fact Sheet 2015.

Sources

  • Beroza, Gregory C.; Cole, Alex T.; Ellsworth, William L. (10 March 1995), "Stability of coda wave attenuation during the Loma Prieta, California, earthquake sequence" (PDF), Journal of Geophysical Research: Solid Earth, 100 (B3): 3977–3987, .