Seismic gap

A seismic gap is a segment of an active fault known to produce significant earthquakes that has not slipped in an unusually long time, compared with other segments along the same structure. There is a hypothesis or theory that states that over long periods of time, the displacement on any segment must be equal to that experienced by all the other parts of the fault.[1] Any large and longstanding gap is, therefore, considered to be the fault segment most likely to suffer future earthquakes.

The applicability of this approach has been criticised by some seismologists[2] although earthquakes sometimes have occurred in previously-identified seismic gaps.

Examples
Cross sections along the San Andreas fault showing recorded seismic activity A) 20 years before the Loma Prieta event, B) The main shock (large circle) and aftershocks for the Loma Prieta event, USGS Circular 1045

Loma Prieta Seismic Gap, California

Prior to the 1989 Loma Prieta earthquake(Mw = 6.9[3]), that segment of the San Andreas fault system recorded much less seismic activity than other parts of the fault.[4] The main shock and aftershocks of the 1989 event occurred within the previous seismic gap.

Central Kuril gap, Russia

Immediately following the 2004 Indian Ocean earthquake, a seismic gap analysis of the seismic zones around the Pacific Ocean identified the Central Kuril segment of the Kuril-Kamchatka Trench subduction zone as the most likely to give rise to a major earthquake.[5] This zone, 500 km in length, at that time had experienced no major earthquake since 1780, but was bounded to north and south by segments that had moved within the last 100 years. The Mw = 8.3 earthquake of 15 November 2006 and the Mw = 8.2 earthquake of 13 January 2007 occurred within the defined gap.

Central Himalayan Gap, India

Although there had been earthquakes to the west (near Delhi) in 1905, and to the east (Nepal–Bihar earthquake) in 1934, there was a 600-kilometer-long region of the central Himalayan that had not ruptured since 1505.[6] In April 2015, the 7.8 Mw April 2015 Nepal earthquake occurred near the center of this region.

References
  1. McCann, W.R., Nishenko, S.P., Sykes, I.R. & Krause, J. 1979. Seismic gaps and plate tectonics: seismic potential for major boundaries. Pure and applied geophysics, 117, 1082–1147
  2. Kagan, Yan Y.; Jackson, David D. (1991). "Seismic Gap Hypothesis: Ten years after". Journal of Geophysical Research: Solid Earth. 96: 21419–21431. Bibcode:1991JGR....9621419K. doi:10.1029/91JB02210.
  3. ANSS: Loma Prieta 1989, Origin (accessed 2019-04-01).
  4. Lessons Learned from the Loma Prieta, California, Earthquake of October 17, 1989. U.S.G.S. Circular 1045 N.B. requires free ie djvu plug-in to view
  5. Baranov, B., Lobkovsky, L., Ivaschenko, A., Kulinich, R. & B. Karp, B. 2007. The Central Kuril Earthquakes and Tsunamis of 15 November 2006 and 13 January 2007: Findings of a Pre-event geophysical field survey. EGU Abstracts
  6. Lutgens, F. K., Tarbuck, E. J., Tasa, D. 2012. Essentials of Geology. Prentice Hall. p 355.
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