If the earth moves beneath our feet, is it because the Seshanaga shrugged?
Seven headed serpent king associated with Lord Vishnu, Seshanaga is generally believed by Hindus to hold the earth on his hoods, and earthquakes are considered to be caused as Seshanaga’s adjusts the massive weight on its hoods.
Not many might believe in Seshanaga theory of earthquake origin, but even today there are earthquake anecdotes that are not remotely supported by the scientific evidence.
Check out if you also have some misconceptions related to earthquakes!
If so, it is high time you clear these, and prepare for the impending major earthquake.
Animals can sense the earthquake
The notion that animals, particularly dogs, can anticipate an impending earthquake predates the birth of Christ, with documented references to unusual animal behaviour as early as 4th century BC. This belief has been fuelled by unauthenticated but well publicised accounts of abnormal animal behaviour before an earthquake from across the world; the most quoted being the magnitude 7.5 Haicheng Earthquake of February 4, 1975 that was successfully predicted.
This notion could however contain a kernel of truth; being generally squat, four-legged, close to the ground, and inclined to sit still, animals might feel or sense the initial weak shaking or the first waves of an earthquake called a P or compressional waves, which roll through just before the obvious movement occurs, and are generally not felt by humans until stronger waves arrive. Some animals could react to these first waves, the P waves — they feel it, and we don’t.
This ability would however be activated only seconds before an earthquake, as there exists no scientific evidence to prove that animals have a built-in early warning system for earthquakes.
Changes have sometimes been observed in animal behaviour prior to earthquakes, but that behaviour has not been consistent, and many a times there has been no perceptible change prior to earthquakes. More so, it is impossible to determine the exact reason of abnormal animal behaviour.
Some scientists have actually tested this hypothesis by analysing shelter records to see if pets run away before an earthquake. That however did not hold good, and there were actually more pet escapes after the earthquake than before.
Every pet owner understands that the pets sometimes behave strangely for n
o apparent reason. And if an earthquake had not subsequently struck, one would not be talking about strange animal behavior — because one wouldn’t have noticed anything out of the ordinary.
This could therefore be yet another example of natural human tendency to look back in time for anomalies, or precursors, that supposedly heralded the coming earthquake.
As far as scientific understanding goes, animals, like humans, have no ability to predict earthquakes.
Earthquakes occur during earthquake weather
The myth of earthquake weather dates back to 4th century BC, the time of the Greek philosopher Aristotle who believed that the winds rumbling around in huge underground caverns, restlessly searching for a way out to the surface cause earthquakes. These earthquake-causing winds being trapped below the ground, there would be no wind above the ground, that in turn would result in unusually hot, and calm weather conditions.
Hot weather, with no wind is thus considered an earthquake precursor.
Despite every region of the world having a story relating to earthquake weather, the depicted weather conditions have distinct variability. In depth investigations show that the depicted weather conditions relate to the most memorable earthquake incidence of that region. People generally tend to notice earthquakes that fit their pattern, and forget the ones that don’t.
To date, a number of studies have been carried out to investigate, and establish a link between weather conditions, and earthquakes. No such link has so far been observed.
Though subdued the belief in earthquake weather has really not died out completely; not even amid the scientific community, and narrated below is one interesting instance wherein a scientist recently tried to predict an earthquake based on observed anomaly in atmospheric temperature.
Located in seismic gap of 1905 Kangara, and 1934 Bihar-Nepal earthquakes, Uttarakhand in Indian Himalaya is considered a high probability region for housing the next big earthquake. In October – November, 2017 the provincial government received a formal notification from Dr. Arun Bapat, a Pune based retired Geophysicist, informing continuing high thermal anomaly in the area around Joshimath in district Chamoli, as deciphered from the data of India Metrological Department (IMD). It expressed possibility of the region being struck by a major earthquake in near future.
On December 29, 2017 Dr.Bapat however communicated that, “There are sufficient scientific evidences to show that a very large magnitude earthquake (M > 7.0) is possible in the Himalayas in the conglomerate of Uttarakhand, Himachal Pradesh, and Jammu and Kashmir. The expected seismic contingency could occur before or by January 10, 2018.”
This created panic amid the authorities, and no one really knew how to react. The information was kept closely guarded, as it was sure to cause panic amongst the masses. Evacuation was neither feasible nor practical, so high alert was sounded for the response agencies. A meeting of various scientific institutions was at the same time organised on January 4, 2018 to reach some consensus to diffuse the crisis.
Dr. Bapat was also present in this meeting. All the scientists present in the meeting were unanimous that there was no scientific basis on which Dr. Bapat had based the earthquake warning. Though present in person, he at the same time could neither explain nor show any anomalous physical evidence that could unquestionably be related to tectonic activity triggering an earthquake. Except for the thermal anomaly Dr. Bapat had nothing substantial, and there occurred no earthquake as was predicted by Dr. Bapat.
Like hot, and unusual calm conditions of earthquake weather, some experts based on their personal experience postulate that it rains after an earthquake, and therefore the ones responsible for post – disaster response should take into account this eventuality. Repeated authoritatively over and over again, people with no first hand experience of earthquakes, as these happen at long intervals, tend to believe this notion. There is no harm really in preparing for the rains after an earthquake but to assert that it would rain after an earthquake is wrong.
Earthquakes, and weather changes are caused by two different physical phenomenons that have no linkage or relationship with each other. Earthquakes really originate many kilometres below the surface of the region witnessing earthquake weather, and there exists no link between the two.
Earthquakes are becoming more frequent
May be because of Fading Affect Bias that makes us forget unpleasant memories, or our not so good tradition of documenting historical events, there exists a general perception across the country that October 20, 1991 Uttarkashi Earthquake was the first major quake to hit the subcontinent, and after that there have been a number of earthquakes in quick succession; September 30, 1993 Latur, May 22, 1997 Jabalpur, March 29, 1999 Chamoli, January 26, 2001 Bhuj, October 8, 2005 Kashmir, September 18, 2011 Sikkim, April 25, 2015 Gorkha, May 12, 2015 Dholka, and April 28, 2021 Sonitpur, Assam.
So people generally think that the frequency of earthquakes is increasing.
Research however shows that the global frequency of large magnitude earthquakes has remained fairly constant throughout the century, and it has actually decreased in recent years. On an average 01 of magnitude 8.0 or more, 18 of magnitude 7.0 – 7.9, 120 of magnitude 6.0 – 6.9, and 800 of magnitude 5.0-5.9 are experienced every year.
However, since there are more seismological centres, and instruments capable of detecting even small earthquakes that went unnoticed previously, it might seem as if there are more earthquakes jolting the earth.
With so many earthquakes in the news— such as those in Haiti, Chile, and Japan — it seems that the frequency of big temblors is on the rise. Here again, there is an element of truth; since the magnitude 9.3 Indian Ocean Earthquake of December 26, 2004 that unleashed a tsunami in the Indian Ocean, the earth has experienced more great earthquakes, with magnitudes near or above 9.0, than the historical average.
The frequency of tremors across the world however fluctuates considerably from year to year. The energy released by big earthquakes since the end of 2004 has been less than the energy released by the two biggest recorded earthquakes; magnitude 9.5 Valdivia Earthquake of May 22, 1960 in Chile, and the magnitude 9.2 Good Friday Earthquake of March 27, 1964 in Alaska. The number of earthquakes with magnitude greater than 7.0 have been somewhat high in recent years, but well within the range throughout the 20th century.
A more worrying trend is illustrated by magnitude 7.0 Haiti Earthquake of January 12, 2010. This earthquake had a devastating toll (100000 – 316000 deaths) despite its relatively modest magnitude because of the prevalence of poorly built structures, and a densely packed population. As both population, and urbanisation expand in developing nations, many more people are exposed to future earthquakes. So even if the frequency of the quakes is not expected to change significantly, the toll these exact is likely to keep rising.
Earthquakes occur during a certain time of year or part of the lunar cycle
There exists a strong belief that lunar cycle has a strong impact on what happens on earth. Taking clues from the influence of lunar cycle on the occurrence of tides, it is asserted that large (Magnitude ≥8) earthquakes occur on preferred days of the calendar year or lunar cycle.
Following this lead the scientists studied all major earthquakes (Magnitude ≥8) from the 1600s to today, and ran an analysis to establish some meaningful pattern as regards time of the year or certain point in the lunar cycle when these occurred. No correlation could however be found.
While the moon does cause tides, it cannot exert stress on solid parts of the earth, as force exerted is not enough to cause or trigger an earthquake.
Ground can open up and swallow people
There has been no recorded case of an earthquake causing cracks to open up, and swallow people or cities. Earthquakes do certainly cause ruptures on the surface of the earth, such as happened during magnitude 6.9 Loma Prieta Earthquake of October 17, 1989. These cracks are generally quite small, and only rarely exceed a meter or two in width. And certainly these cracks do not again close up, and swallow somebody or something.
The cracks observed on the surface after an earthquake are generally not actual ground ruptures, but are instead ground failures.
In fact, there is only one case in which a cow reportedly died as a direct result of being trapped in an earthquake-caused crack. One of the researchers studying the impacts of April 18, 1906 San Francisco Earthquake of magnitude 7.8 along the San Andreas Fault documented a farmer’s narration from close to Point Reyes National Seashore that is famously known as Lawson Report, “During the earthquake a cow fell into the fault crack, and the earth closed in on her so that only the tail remained visible. At the time of my visit, the tail had disappeared, being eaten by dogs.”
The farmer who showed people his cow later recanted, saying he merely pushed the cow (which died of natural causes) into the crevasse.
It is important to note that the ground actually moves across a fault during an earthquake, not away from it. If the fault could open to swallow objects, and people, there would be no friction, and without friction, there would be no earthquake.
Shallow crevasses do form during an earthquake induced landslide or other types of ground failure. Faults, however, do not gape open during an earthquake.
Doorway is the safest place to be during an earthquake
During the earthquake safety lessons we often hear that one should remain under the doorway during an earthquake, and most of us take it for granted. This is however true only for an unreinforced house. In a modern beam-column structure the doorway is no stronger than rest of the building, and one might actually be hurt there by wildly swinging door. And in a public building, one could be hurt there by people trying to rush out.
So if you are inside a building during an earthquake, try “drop, cover and hold” maneuver under a sturdy piece of furniture. If indoors, stay there, drop to the floor, make yourself small, and get under a desk or table or stand in a corner.
If outdoors, get into an open area away from trees, buildings, walls, and power lines.
If in a high-rise building, stay away from windows, and outside walls, stay out of elevators, and get under a table.
If driving, pull over to the side of the road, and stop. Avoid overpasses, and power lines. Stay inside your car until the shaking is over.
If in a crowded public place, do not rush for the doors. Crouch, and cover your head, and neck with your hands, and arms.
Aftershocks are no cause of worry
Aftershock refers to relatively small magnitude earthquakes that follow a big earthquake, and are experienced in the effected area for a long time. These are generally related with post-earthquake crustal adjustments.
Aftershock are generally considered somewhat less worrisome incidence.
As per scientific understanding, an aftershock of a certain magnitude is however no different from an independent temblor of a similar magnitude. The shaking, and rupture are the same, and the energy released is also the same.
And aftershocks could in fact be more damaging than larger main shock if these strike close to population centres. This lesson was very nicely illustrated by Canterbury earthquake series that occurred within and near the city of Christchurch in New Zealand, and the Canterbury Plains region between September 2010 and late December 2011.
The principal event, the 7.1 magnitude Darfield Earthquake struck on September 4, 2010 with epicentre some 40 km west of Christchurch near the town of Darfield, and focus about 10 km beneath the surface.
Rather than the main Darfield Earthquake event major losses were caused by a 6.3 magnitude aftershock that occurred on February 22, 2011. In contrast to the main shock, this aftershock had relatively shallow focus; 5 km beneath the surface of Heathcote Valley, a suburb of Christchurch located on the Banks Peninsula.
Shallow depth, and close proximity to Christchurch contributed to substantial shaking, surface cracking, and liquefaction in the city, and surrounding areas. Buildings, and roads across the Christchurch region, which had been weakened by the September 4, 2010 Darfield Earthquake, and its aftershocks were severely damaged or destroyed in this event. Christchurch’s city centre was hit particularly hard, and was evacuated. More than 180 people died in this quake; many of them were killed outright as structures collapsed, and debris fell in the streets, crushing cars, and buses as well.
Moreover, it needs to be remembered that the aftershocks need not necessarily be low magnitude tremors.
7.5-7.9 magnitude New Madrid Earthquake of December 16, 1811 was followed the same day by a 7.4 magnitude aftershock. 7.8 magnitude Kaikoura Earthquake of November 14, 2016 was followed by aftershocks of 5.6, 5.9, and 6.5 magnitude. 7.8 magnitude Gorkha Earthquake of April 25 was followed by 7.3 magnitude aftershock; Dolakha Earthquake of May 12, 2015.
Big earthquakes always occur early in the morning
Just as earthquakes do not care about the weather, they do not observe time. May 18, 1940 El Centro or Imperial Valley Earthquake struck at 9:36 PM, while October 17, 1989 Loma Prieta Earthquake struck at 5:02 PM. April 25, 2015 Gorkha, and May 12, 2015 Dhokla earthquakes struck at 11:56 AM, and 0:50 PM respectively.
People who perpetuate time, and weather myths generally tend to remember the earthquakes that fit their pattern, and forget the ones that don’t.
Small earthquakes keep big ones at bay
Sometimes people tend to regard frequently occurring low magnitude earthquakes as safety valve that lessen the chances of the area being hit by a large magnitude earthquake, as the accumulated energy gets dissipated regularly.
This however is not true, and to better appreciate this it is important to understand the earthquake magnitude scale that was introduced by Charles Richter in 1935.
The Richter Scale is logarithmic, which simply means that progressively bigger quakes are a lot more powerful than smaller quakes. For each unit increase in magnitude (i.e., going from 5.7 to 6.7), the energy released rises by a factor of about 30 — meaning that a two-unit increase would translate into an earthquake that is nearly 1,000 times as severe.
If enough stress has built up on a fault to generate a magnitude 7.0 earthquake, it would take about 1000 earthquakes of magnitude 5.0 to release the equivalent energy. In nature, events however don’t happen that way.
In any given area, the number of tremors of different magnitude almost always follow a simple mathematical progression, with about 10 magnitude 6.0 quakes, and about 100 magnitude 5.0 quakes for every single magnitude 7.0 quake. Thus, if there is significant strain energy to be released, it must be released in large earthquakes.
So while small earthquakes may temporarily ease the stress on a fault line, these in no way prevent a large earthquake.
So, if your area has not been struck by a big earthquake for a long time, it is real cause of concern. Scientists identify such areas as Seismic Gap that have high potential of housing a large magnitude earthquake. Despite having witnessed magnitude 6.8 Uttarkashi Earthquake of October 20, 1991, and magnitude 6.6 Chamoli Earthquake of March 29, 1999, Uttarakhand has not witnessed a major earthquake since magnitude 7.5 Garhwal Earthquake of September 1, 1803, and is recognized as falling in Seismic Gap of magnitude 7.8 Kangara Earthquake of April 4, 1905, and magnitude 8.0 Bihar – Nepal Earthquake of January 15, 1934. Uttarakhand Himalaya is thus identified as a potential candidate for housing a major earthquake in near future which is a cause of major concern for the densely populated northern Indo-Gangetic plains.
Moreover, immense stresses are regularly being accumulated due to the movement of massive plates of continental dimensions. So, even a large magnitude earthquake is no guarantee of safety from yet another large magnitude earthquake; 7.5-7.9 magnitude New Madrid Earthquake of December 16, 1811 was followed the same day by a 7.4 magnitude earthquake while 7.8 magnitude Gorkha Earthquake of April 25, 2015 was followed by 7.3 magnitude Dolakha Earthquake on May 12, 2015
We have good building codes so we must have good buildings
That is only theoretically true, and applies only to buildings constructed under current building codes. Moreover what is prescribed in the codes has to be actually followed during construction to ensure safety of the buildings.
Engineers use the knowledge acquired from previous earthquakes to make structures safer in the event of major earthquakes. Local officials at the same time enact new building codes to ensure that the new buildings are built taking note of earthquake safety concerns. This includes both improving the design of new structures as well as strengthening older units to incorporate the latest advances in seismic, and structural engineering.
But the best building codes in the world do nothing for buildings built before that code was enacted. While the codes have been updated, the older buildings are still in place. Fixing problems in older buildings— known as retrofitting— is a tedious job, and undertaken on a limited scale. Even though authorities actively identify old buildings for retrofitting, there would still remain large stock of out-of-date structures.
Moreover, a building that was deemed earthquake-safe decades ago might not comply to the present seismic safety standards.
Moreover, being up to code is also based on probability — not exceeding a 2% chance of collapse in 50 years. Those are pretty good odds, but even if your home or office doesn’t crash like a stack of pancakes it is not necessarily safe. You might lose all the building contents or it might have to be torn down ultimately as there is no such thing as earthquake-proof.
There is a lot we don’t know about earthquakes. One thing we do know is how to be prepared; something many people in earthquake-prone regions neglect. Even basic steps like securing bookshelves, and water heaters to walls or stocking up on disaster supplies could significantly impact your well being after a big quake. And it is always better to over-prepare than being caught unprepared.
Big earthquakes always occur during the night
October 20, 1991 Uttarkashi, and March 29, 1999 Chamoli earthquakes struck at 2:53 AM, and 0:35 AM respectively but then recently October 8, 2005 Mujaffarabad, April 25, 2015 Gorkha, and May 12, 2015 Dhokla earthquakes struck at 8:50 AM, 11:56 AM, and 0:50 PM respectively.
Just as earthquakes do not care about the weather, they do not follow the time. People who perpetuate time, and weather myths often tend to remember the earthquakes that fit their pattern, and generally forget about the ones that don’t.
There is nothing I can do about earthquakes
In reality it is an alibi resorted to by people to cover up their inaction.
It is true that earthquakes can neither be stopped nor predicted, but you can be prepared. You can prepare an earthquake kit, practice duck, cover and hold drills at home with your family, and at work, make your home, and office earthquake safe, practice first aid, as also what you would or won’t do during or after an earthquake, and develop an earthquake plan; where would you meet the family members if you were not together when an earthquake hit.
Mega-quakes can happen
Strictly speaking, mega-quakes of magnitude 10.0 or more are possible; however, scientists agree that they are implausible. The magnitude of an earthquake is a function of the length of the fault on which it occurs — the longer the fault, the larger the earthquake. The San Andreas Fault is only 1300 km long. Rupture of a fault many times the length of the San Andreas Fault would be required to generate a magnitude 10.5 earthquake. No fault long enough to generate a magnitude 10.5 earthquake is however known to exist.
Magnitude 9.5 Valdivia Earthquake that struck Chile on May 22, 1960 is the largest earthquake ever recorded. This was a shallow focus (33 km) megathrust earthquake associated with the subducting Nazca Plate, and the South American Plate, on the Peru–Chile Trench, and the earthquake rupture zone extended for 800 km from Arauco (37° S) to Chiloé Archipelago (43° S).
Earthquakes can be prevented
We can neither prevent earthquakes from happening nor stop them once they have started.
We can however significantly mitigate their effects by characterising the hazard; identifying earthquake faults, unconsolidated sediment likely to amplify earthquake waves, and unstable land prone to sliding or liquefying during strong shaking, building safer structures, and preparing in advance by taking preventative measures, and knowing how to respond.
Earthquakes can be predicted
Earthquake prediction is the holy grail for earthquake scientists, but currently there exists no accepted method to accomplish the goal of predicting the time, place, and magnitude of an impending earthquake.
Research into earthquake prediction however continues.
The approach of most scientists has however been to focus on providing long-range forecasts of the likely locations, and impacts of damaging earthquakes. For example, scientists estimate that over the next 30 years the probability of a major earthquake occurring in the San Francisco Bay area is 62%, and 60% in Southern California. Based on geology, and earthquake history of the region scientists are also able to predict the type of ground motion to be expected. Engineers, and building code developers use these models of site response to improve the safety of structures, thereby reducing the ultimate earthquake risk.
Everyone would panic during the Big One
A common belief is that people always panic, and run around madly during, and after earthquakes, creating more danger for themselves, and others.
Actually, research shows that people usually take protective actions, and help others both during, and after the shaking.
Most people don’t get too shaken up about being shaken up.
Earthquakes kill people
In an earthquake, the severity of the shaking can cause manmade, and natural structures, and the contents within these to fail or fall, and injure or kill people.
There have however been large earthquakes with very little damage because these caused little shaking, and/or the buildings were built to withstand that shaking.
In other cases, smaller earthquakes have caused great shaking, and/or buildings collapsed as these were never designed or built to survive shaking. This is exactly what caused massive loss (100000 -316000 deaths) in magnitude 7.0 Haiti Earthquake of January 12, 2010. This earthquake had a devastating toll despite its relatively modest magnitude because of a prevalence of poorly built structures, and a densely packed population.
Much therefore depends on two variables; geology, and engineering.
There are variations in geological set up from place to place, both at and below the ground surface. Differences in geology result in quite different earthquake response; ground shaking at a site with soft sediments could last 3 times as long as shaking at a stable bedrock site such as one composed of granite.
Local soil conditions also play a major role, as certain soils greatly amplify the ground shaking in an earthquake. A soft, loose soil would shake more intensely than hard rock at the same distance from the same earthquake.
Fires are another major risk during earthquakes as gas lines may be damaged, and be particularly hazardous.
As both population, and urbanization expand in developing nations, many more people are exposed to future earthquakes. So even if the frequency of quakes is not expected to change significantly, the toll these exact is likely to keep rising.
A good compilation of facts. Thanks for sharing.