{"id":19827,"date":"2025-06-16T07:31:27","date_gmt":"2025-06-16T07:31:27","guid":{"rendered":"https:\/\/www.ierek.com\/news\/?p=19827"},"modified":"2025-06-16T07:54:36","modified_gmt":"2025-06-16T07:54:36","slug":"earthquake-causes-vs-triggers","status":"publish","type":"post","link":"https:\/\/www.ierek.com\/news\/earthquake-causes-vs-triggers\/","title":{"rendered":"Earthquake Causes vs. Triggers"},"content":{"rendered":"

 <\/p>\n

One<\/span>\u00a0<\/span>of the\u00a0<\/span>fundamental\u00a0<\/span>concepts<\/span> in seismology, necessary for scientific studies and pragmatically <\/span>useful\u00a0<\/span>hazard assessment, is differentiating<\/span>\u00a0<\/span>of\u00a0<\/span>earthquake causes and earthquake triggers. Earthquake causes refer to <\/span>those<\/span>\u00a0long-term<\/span>\u00a0<\/span>deep-seated<\/span>\u00a0<\/span>earth<\/span>\u00a0forces that lead to the\u00a0<\/span>accumulation<\/span>\u00a0of elastic\u00a0<\/span>energy\u00a0<\/span>in<\/span>\u00a0the Earth’s crust. This\u00a0<\/span>is<\/span>\u00a0the continuous movement and interaction of\u00a0<\/span>the\u00a0<\/span>tectonic plates, which\u00a0<\/span>builds<\/span>\u00a0<\/span>stress\u00a0<\/span>slowly<\/span>\u00a0<\/span>in\u00a0<\/span>faults. This causative process\u00a0<\/span>operates<\/span>\u00a0over\u00a0<\/span>large<\/span>\u00a0geological timescales,\u00a0<\/span>ranging\u00a0<\/span>from decades to centuries or\u00a0<\/span>millennia,\u00a0<\/span>by<\/span>\u00a0<\/span>slowly\u00a0<\/span>accumulating<\/span>\u00a0<\/span>stress\u00a0<\/span>in\u00a0<\/span>locked\u00a0<\/span>segments of faults<\/span>.<\/span><\/div>\n

<\/h2>\n

Earthquake Triggers: The Immediate Precursors<\/b><\/h2>\n

Triggers are distinct from causes; they are specific events or activities that impart the final perturbation to an already critically stressed fault, initiating the sudden rupture and discharge of accumulated energy.<\/span><\/p>\n

However earthquake triggers do not cause the source stress build-up but rather accelerate or initiate the release of pre-stored stress, which has accumulated due to geological forces over a long time. A most noteworthy result in crustal mechanics is that Earth’s crust as a whole is essentially stressed very close to its failure point even in tectonically quiescent areas.<\/span><\/p>\n

This unstable state means that even relatively small natural or artificial perturbations of the local stress field are sufficient to cause an earthquake.<\/span><\/p>\n

<\/h3>\n

Natural Earthquake Triggers<\/b><\/h3>\n

Dynamic Stress Transfer<\/b><\/h4>\n

Large earthquakes can occasionally induce subsequent seismic activity hundreds of kilometers away through dynamic stress transfer. This is because seismic waves from the original earthquake shake energy around the globe, causing a new earthquake.<\/span><\/p>\n

The stress released from a mainshock can reallocate and concentrate on neighboring faults. A buildup as small as 1% can be enough to advance the timing of the next earthquake on a maximally stressed fault. The 1992 M7.3 Landers earthquake triggered seismicity all over California, for example, and the 2004 M9.1 Sumatra earthquake triggered activity as far away as Alaska.<\/span><\/p>\n

\"1992
The Landers earthquake, which had a moment magnitude (Mw) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone..<\/figcaption><\/figure>\n

 <\/p>\n

Slow Slip Events (SSEs)<\/b><\/h4>\n

Slow slip events are “slow motion” earthquakes that build up over days, weeks, or months, unlike typical rapid quakes. These prolonged slips can cause bigger, more devastating earthquakes, such as the 2011 M9.0 Tohoku earthquake in Japan. Large earthquakes can trigger slow slip events, showing an intricate, symbiotic relationship between rapid and slow fault motion.<\/span><\/p>\n

\"2011
On March 11, 2011, a magnitude (Mw) 9.1 earthquake struck off the northeast coast of Honshu on the Japan Trench. A tsunami that was generated by the earthquake arrived at the coast within 30 minutes, overtopping seawalls and disabling three nuclear reactors within days.<\/figcaption><\/figure>\n

Volcanic Activity<\/b><\/h4>\n

Even more infrequently, major regional earthquakes (M6+) can cause eruptions or unrest at volcanoes. However this can only occur if the volcano is already primed to erupt with plenty of magma and is unstable. The earthquake in this case acts as a spark, pushing an already unstable volcanic system beyond its eruptive threshold, illustrating how seismic energy has the ability to disrupt magmatic systems.<\/span><\/p>\n

 <\/p>\n

Human-Induced Triggers<\/b><\/h3>\n

Human activities can cause earthquakes by disturbing the fine balance of stress in the Earth’s crust. Although these activities do not generate the tectonic stress, they can deliver the key “push” needed to release the stored energy. Some of the major human activities that create seismicity are:<\/span><\/p>\n

Table 1: Common Human-Induced Earthquake Triggers<\/b><\/p>\n\n\n\n\n\n\n\n\n
Activity<\/b><\/td>\nMechanism of Triggering<\/b><\/td>\nExamples<\/b><\/td>\n<\/tr>\n
Fluid Injection (Wastewater Disposal, Fracking)<\/span><\/td>\nAlters pore pressure, reduces friction on faults<\/span><\/td>\nOklahoma, Colorado, Ohio, Arkansas (wastewater); various fracking sites<\/span><\/td>\n<\/tr>\n
Fluid Withdrawal (Oil\/Gas, Groundwater)<\/span><\/td>\nChanges pore pressure and stress distribution<\/span><\/td>\nLorca, Spain (groundwater); historical fossil fuel production in Oklahoma\/Texas<\/span><\/td>\n<\/tr>\n
Reservoir Impoundment<\/span><\/td>\nAdds an enormous load to the ground, altering the stress<\/span><\/td>\nKoyna Dam (India), Oroville Dam (California)<\/span><\/td>\n<\/tr>\n
Mining Activities<\/span><\/td>\nChanges the stress distribution due to material removal<\/span><\/td>\nGermany (salt, coal mining)<\/span><\/td>\n<\/tr>\n
\n

Geothermal Power Plants<\/span><\/p>\n<\/td>\n

\n

Extraction\/injection of hot, pressurized water alters local stress<\/span><\/p>\n<\/td>\n

\n

Salton Sea (California)<\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

<\/h4>\n

Fluid Injection and Withdrawal:<\/b><\/h4>\n