A seismic gap is a segment of an
active fault
An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...
known to produce significant
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
s 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. 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 although earthquakes sometimes have occurred in previously-identified seismic gaps.
Examples
Loma Prieta Seismic Gap, California
Prior to the
1989 Loma Prieta earthquake
The 1989 Loma Prieta earthquake occurred on California's Central Coast on October 17 at local time. The shock was centered in The Forest of Nisene Marks State Park in Santa Cruz County, approximately northeast of Santa Cruz on a section of t ...
( = 6.9), that segment of the
San Andreas fault
The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonics, tectonic boundary between the Pacific Plate and the North American Plate, and its motion is Fault (geology)#Strike-slip fau ...
system recorded much less seismic activity than other parts of the fault. The main shock and
aftershock
In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...
s of the 1989 event occurred within the previous seismic gap.
Central Kuril gap, Russia
Immediately following the
2004 Indian Ocean earthquake
An earthquake and a tsunami, known as the Boxing Day Tsunami and, by the scientific community, the Sumatra–Andaman earthquake, occurred at 07:58:53 local time (UTC+7) on 26 December 2004, with an epicentre off the west coast of northern Suma ...
, a seismic gap analysis of the seismic zones around the Pacific Ocean identified the Central Kuril segment of the
Kuril–Kamchatka Trench
The Kuril–Kamchatka Trench or Kuril Trench (russian: Курило-Камчатский жёлоб, ''Kurilo-Kamchatskii Zhyolob'') is an oceanic trench in the northwest Pacific Ocean. It lies off the southeast coast of Kamchatka and parallels ...
subduction
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
zone as the most likely to give rise to a major earthquake. 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 = 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.
[Lutgens, F. K., Tarbuck, E. J., Tasa, D. 2012. Essentials of Geology. Prentice Hall. p 355.] In April 2015, the 7.8
April 2015 Nepal earthquake
The April 2015 Nepal earthquake (also known as the Gorkha earthquake) killed 8,964 people and injured 21,952 more. It occurred at on Saturday, 25 April 2015, with a magnitude of 7.8 Mw or 8.1 Ms and a maximum Mercalli Intensity of X (''Extreme ...
occurred near the center of this region.
References
External links
USGS glossary entry
{{DEFAULTSORT:Seismic Gap
Seismology