question: When tectonic plates shift, why is there only an earthquake in a single place and not all along the plates' boundaries?
comment: As plates try to shift, the plate becomes locked as rocks on one side catch on rocks on the other side. The plate bends as the forces build up and the catch point gives, and you get an earthquake. This shifts load to other catch points, that might then give - these are aftershocks. These quakes release the tension in that area of the plates. Another sequence of quakes will happen mearby, releasing tensions in that area. All these small shifts happening over the centuries makes up a shift in the tectonic plates.
passages: The applicability of this approach has been criticised by some seismologists although earthquakes sometimes have occurred in previously-identified seismic gaps.
  
  Section::::Examples.
  
  Section::::Examples.:Loma Prieta Seismic Gap, California.
  
  Prior to the 1989 Loma Prieta earthquake, that segment of the San Andreas fault system recorded much less seismic activity than other parts of the fault. The main shock and aftershocks of the 1989 event occurred within the previous seismic gap.
  
  Section::::Examples.:Central Kuril gap, Russia.
   BULLET::::2. The "in situ" model predicts numerous normal faults overlying one large décollement.
  
  BULLET::::3. The rooted, low angle normal fault model predicts that the décollement is created when two thin sheets of rock decouple at depth. Near the thickest part of the upper plate, extensional faulting may be negligible or absent, but as the upper plate thins, it loses its ability to remain coherent and may behave as a thin-skinned extensional terrane.
   Overlapping spreading centers are found mostly on mid-ocean ridge spreading centers in the Pacific Ocean basin where the rates of separation between the plates are higher than in other ocean basins. They occur on all fast-spreading rate centers (90 mm/yr) including the East Pacific Rise, and on most intermediate-rate spreading centers (50–90 mm/yr), such as the Galapagos Spreading Center, the Juan de Fuca Ridge and the Pacific-Antarctic Ridge.
   Earthquakes are common along convergent boundaries. A region of high earthquake activity, the Benioff zone, generally dips 45° and marks the subducting plate. Earthquakes will occur to a depth of 670  km along the Benioff. Both compressional and extensional forces act along convergent boundaries. On the inner walls of trenches, compressional faulting or reverse faulting occurs due to the relative motion of the two plates. Reverse faulting scrapes off ocean sediment and leads to the formation of an accretionary wedge. Reverse faulting can lead to massive earthquakes, such as the magnitude 9.1 Sumatra earthquake of 2004.  Tensional or normal faulting occurs on the outer wall of the trench, likely due to bending of the down going slab.
   Current research indicates that complex convection within the Earth's mantle allows material to rise to the base of the lithosphere beneath each divergent plate boundary. 
  
  This supplies the area with vast amounts of heat and a reduction in pressure that melts rock from the asthenosphere (or upper mantle) beneath the rift area forming large flood basalt or lava flows. Each eruption occurs in only a part of the plate boundary at any one time, but when it does occur, it fills in the opening gap as the two opposing plates move away from each other.
   Areas of the crust where new crust is created are called "divergent boundaries", those where it is brought back into the earth are "convergent boundaries" and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform (or conservative) boundaries Earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction.
   Major fault boundaries within rift systems tend to expand with time based on the assumption that the extensional stress and strain is consistent in a given rift system. Transfer zones have been identified according to the fault propagation evolution; they include approaching, overlapping, collateral, and collinear. This classification assists in visualization and deformational history of the transfer zone.
  
  Section::::Transfer zone fault propagation evolution.:Approaching.
  
  When transfer zones are in the approaching stage the major boundary faults have not propagated past one another yet.
  
  Section::::Transfer zone fault propagation evolution.:Overlapping.
   Intraplate earthquakes are relatively rare compared to the more familiar boundary-located interplate earthquakes. Therefore, large intraplate earthquakes can inflict heavy damage with such areas' structures lacking seismic retrofitting. Examples of damaging intraplate earthquakes are the devastating Gujarat earthquake in 2001, the 2012 Indian Ocean earthquakes, the 2017 Puebla earthquake, the 1811–1812 earthquakes in New Madrid, Missouri, and the 1886 earthquake in Charleston, South Carolina.
  
  Section::::Fault zones within tectonic plates.
   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. 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 M = 8.3 earthquake of 15 November 2006 and the = 8.2 earthquake of 13 January 2007 occurred within the defined gap.
  
  Section::::Examples.:Central Himalayan Gap, India.
   Some of the deadliest natural disasters have occurred due to convergent boundary processes. The 2004 Indian Ocean earthquake and tsunami was triggered by an earthquake along the convergent boundary of the Indian plate and Burma microplate and killed over 200,000 people.  The 2011 tsunami off the coast of Japan, which caused 16,000 deaths and did US$360 billion in damage, was caused by a magnitude 9 earthquake along the convergent boundary of the Eurasian plate and Pacific Plate.
  
  Section::::Examples.
  
  BULLET::::- The collision between the Eurasian Plate and the Indian Plate that is forming the Himalayas.
   Earthquakes may occur regularly here because the location is about midway on a fault segment between a "locked" segment to the south (last major earthquake 1857) and a "creeping" segment to the north where two tectonic plates are continuously moving without major earthquakes.
  
  Section::::Research.
   The surface of the Earth is made up of seven primary and eight secondary tectonic plates, plus dozens of tertiary microplates. The large plates move very slowly, owing to convection currents within the mantle below the crust. Because they do not all move in the same direction, plates often directly collide or move laterally along each other, a tectonic environment that makes earthquakes frequent. Relatively few earthquakes occur in intraplate environments; most occur on faults near plate margins. By definition, intraplate earthquakes do not occur near plate boundaries, but along faults in the normally stable interior of plates. These earthquakes often occur at the location of ancient failed rifts, because such old structures may present a weakness in the crust where it can easily slip to accommodate regional tectonic strain.
   In 2001, a large intraplate earthquake devastated the region of Gujarat, India. The earthquake occurred far from any plate boundaries, which meant the region above the epicenter was unprepared for earthquakes. In particular, the Kutch district suffered tremendous damage, where the death toll was over 12,000 and the total death toll was higher than 20,000.
  
  In 2017, the 24–29 km deep magnitude 6.5 Botswana earthquake that shook eastern Botswana occurred at over 300 km from the nearest active plate boundary. The event occurred in an underpopulated area of Botswana.
  
  The 1888 earthquake in Río de la Plata was also an intraplate quake.
   Research by Rezene Mahatsente indicates that the driving stresses caused by ridge push would be dissipated by faulting and earthquakes in plate material containing large quantities of unbound water, but they conclude that ridge push is still a significant driving force in existing plates because of the rarity of intraplate earthquakes in the ocean.
   Convergent margins where the angle of subduction is oblique will often result in the partitioning of strain into an arc parallel component (accommodated by strike slip faults or shear zones) and an arc normal component (accommodated through thrust faults). This occurs as a response to shear stress exerted at the base of the overriding plate that is not perpendicular to the plate margin.
  
  Section::::Superposition of individual strain components.:Oblique convergent margins.:Fundamental factors which control strain partitioning within oblique orogens.
  
  BULLET::::- Stress Orientation:Subduction angle – Increased subduction angle increases arc parallel component
   Divergent boundaries are typified in the oceanic lithosphere by the rifts of the oceanic ridge system, including the Mid-Atlantic Ridge and the East Pacific Rise, and in the continental lithosphere by rift valleys such as the famous East African Great Rift Valley. Divergent boundaries can create massive fault zones in the oceanic ridge system. Spreading is generally not uniform, so where spreading rates of adjacent ridge blocks are different, massive transform faults occur. These are the fracture zones, many bearing names, that are a major source of submarine earthquakes. A sea floor map will show a rather strange pattern of blocky structures that are separated by perpendicular to the ridge axis. If one views the sea floor between the fracture zones as conveyor belts carrying the ridge on each side of the rift away from the spreading center the action becomes clear. Crest depths of the old ridges, parallel to the current spreading center, will be older and deeper... (from thermal contraction and subsidence).
   Orogenic belts can form during the assembly of continents and supercontinents. The orogenic belts present on continental blocks are classified into three different categories and have implications of interpreting geologic bodies. Intercratonic orogenic belts are characteristic of ocean basin closure. Clear indicators of intercratonic activity contain ophiolites and other oceanic materials that are present in the suture zone. Intracratonic orogenic belts occur as thrust belts and do not contain any oceanic material. However, the absence of ophiolites is not strong evidence for intracratonic belts, because the oceanic material can be squeezed out and eroded away in an intercratonic environment. The third kind of orogenic belt is a confined orogenic belt which is the closure of small basins. The assembly of a supercontinent would have to show intercratonic orogenic belts. However, interpretation of orogenic belts can be difficult.
   All tectonic plates have internal stress fields caused by their interactions with neighboring plates and sedimentary loading or unloading (e.g. deglaciation). These stresses may be sufficient to cause failure along existing fault planes, giving rise to intraplate earthquakes.
  
  Section::::Naturally occurring earthquakes.:Shallow-focus and deep-focus earthquakes.
   Sometimes a series of earthquakes occur in what has been called an "earthquake storm", where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, and with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the North Anatolian Fault in Turkey in the 20th century and has been inferred for older anomalous clusters of large earthquakes in the Middle East.
   BULLET::::4. Décollements can form from high angle normal faults. Uplift in a second stage of extension allows the exhumation of a metamorphic core complex (see Fig. 2). A half graben forms, but stress orientation is not perturbed due to high fault friction. Next, elevated pore pressure (Pp) leads to low effective friction that forces σ1 to be parallel to the fault in the footwall. A low-angle fault forms and is ready to act as décollement. Then, the upper crust is thinned above the décollement by normal faulting. New high-angle faults control the propagation of the décollement and help crustal exhumation. Finally, major and rapid horizontal extension lifts the terrain isostatically and isothermally. A décollement develops as an antiform that migrates toward shallower depths.
   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. Any large and longstanding gap is, therefore, considered to be the fault segment most likely to suffer future earthquakes.
   Intrabasin transfer zones are within the constraints of the interbasin transfer zones and are normally an order of magnitude smaller. Intrabasin transfer zones could be relay ramps within en echelon normal faults, or minor fault jogs. The southern margin of the Gulf of Evvia near Atalanti shows the magnitude of difference between interbasin transfer zones with accommodating distances up to 10 km as well as intrabasin transfer zones that accommodate approximately 1 km or less.
  
  Section::::Synthetic transfer zones.
   At the contact where two tectonic plates slip past each other every section must eventually slip, as (in the long-term) none get left behind. But they do not all slip at the same time; different sections will be at different stages in the cycle of strain (deformation) accumulation and sudden rebound. In the seismic gap model the "next big quake" should be expected not in the segments where recent seismicity has relieved the strain, but in the intervening gaps where the unrelieved strain is the greatest. This model has an intuitive appeal; it is used in long-term forecasting, and was the basis of a series of circum-Pacific (Pacific Rim) forecasts in 1979 and 1989–1991.
   At the contact where two tectonic plates slip past each other every section must eventually slip, as (in the long-term) none get left behind. But they do not all slip at the same time; different sections will be at different stages in the cycle of strain (deformation) accumulation and sudden rebound. In the seismic gap model the "next big quake" should be expected not in the segments where recent seismicity has relieved the strain, but in the intervening gaps where the unrelieved strain is the greatest. This model has an intuitive appeal; it is used in long-term forecasting, and was the basis of a series of circum-Pacific (Pacific Rim) forecasts in 1979 and 1989–1991.
   Propagation may take place on a single fault, but in many cases the rupture starts on one fault before jumping to another, sometimes repeatedly. The 2002 Denali earthquake initiated on a thrust fault, the Sutsina Glacier Thrust, before jumping onto the Denali Fault for most of its propagation before finally jumping again onto the Totschunda Fault. The rupture of the 2016 Kaikoura earthquake was particularly complex, with surface rupture observed on at least 21 separate faults.
  
  Section::::Termination.
  