The National Seismological Service (SSN) reported that as of 18:00 hours this Friday, September 10, 569 aftershocks have been registered from last Tuesday's 7.1 magnitude earthquake with an epicenter near Acapulco in the state of Guerrero. In its latest update, the SSN reported that the largest aftershock of the earthquake is still of magnitude 5.2, which occurred only minutes ago.

Through its Twitter account, the Seismologico reported the following on its latest aftershock cutoff: "As of 18:00 hours on 10/September/2021, 569 aftershocks have been recorded from the M 7.1 earthquake that occurred in Guerrero on 07/September/2021, the largest of M 5.2.", reads the SSN's Twitter account.

Users questioned the National Seismological Service about whether so many aftershocks are normal since in just a few days hundreds of small earthquakes have been registered in the same area. In this regard, the SSN has not responded recently, however, on other occasions they have already given answers to this question of the curious.

Why do earthquake aftershocks occur?

The National Seismological Service reported that when an earthquake of considerable magnitude occurs, the rocks near the rupture zone are subject to a rearrangement. During this process, a series of earthquakes known as aftershocks are generated, which are of lesser magnitude and can occur minutes, days, and even years after the main event.

The number of these aftershocks can vary from a few earthquakes to hundreds of events. The magnitude of an earthquake is differentiated by the data and methodology used, the SSN reports that the Coda Magnitude (Mc) is used for earthquakes of magnitude less than 4.5 and is obtained from the duration of the record. For those of greater intensity, they use the Energy Magnitude (EM) with epicenter in Guerrero and Amplitude Magnitude (AM) for Mexico.

How an earthquake occurs

An earthquake occurs when the efforts affecting a certain volume of rock exceed its resistance, causing a violent rupture and the sudden release of accumulated energy. This energy propagates in the form of seismic waves in all directions.


The magnitude of an earthquake is a number related to the amount of energy released at the time of its occurrence. It is calculated using the records of one or more seismographs and is expressed by means of Arabic numbers, including decimal fractions, where necessary. A given degree of magnitude implies about 32 times more energy released than the previous one. Thus, an earthquake of magnitude 7 is 32 times more energetic than one of 6 and about 1000 times bigger than one of 5.

The first magnitude scale was defined by C.F. Richter in 1932. Nowadays, considering the different types of earthquakes, their depths, etc., seismologists handle several magnitude scales.


The intensity of an earthquake is associated with a particular place and is assigned according to the effects caused on man, his buildings, and the natural terrain of the locality. To assign a degree of intensity, the modified Mercalli scale is used, which uses Roman numerals, from I to XII.

What to do before, during, and after an earthquake

The frequency of earthquakes in the country and the number of vulnerable areas require that preventive measures be taken that can mitigate or reduce the effects of these phenomena. The most common personal accidents are the result of:

Partial collapses of buildings, which cause dividing walls, cornices, canopies, false ceilings, and lighting units to fall.

Fall of broken glass from windows.

Fall of bookshelves, furniture, and other items inside buildings.


Fall of electrical energy cables.

Human acts caused by panic (e.g. running into the street, pushing others, etc.)

A person can reduce the dangers to which they and their family are exposed by learning what to do in case of an earthquake.

Before / How to prepare for earthquake

Go to the Civil Protection unit or local authorities for instructions on:

If the area you live in may be affected by intense seismic movements.

What protective measures you should take at home or at work in the event of an earthquake.

How you can collaborate with the relief brigades if you are interested in training to participate in this situation.

Have a battery-powered radio, flashlight, and personal documents on hand.

Make sure your home or workplace is at least as safe:

Engage the services of an engineer, architect, or master builder to detect the most vulnerable parts of your home in an earthquake and identify the safest places to protect yourself.

Have your gas and electricity installations periodically checked and repaired, if necessary, so that they are always in good condition.

Prepare, study and practice with your family or co-workers a plan to use in case of an earthquake.

Instruct all family members about how and where to turn off gas and electricity supplies.

Assemble a first aid kit.

Have the emergency phone numbers of the Red Cross, Civil Protection, hospitals, fire department, police, etc. available.

Arrange with your family members the address of a known person outside the area where you live, to communicate or meet there, in case they become separated.

Agree on what each family member or co-worker will do in the event of an earthquake.

Place large, heavy objects on shelves or in low places.

Attach pictures, mirrors, cupboards, bookcases, and shelves to the wall. Avoid placing heavy objects on top of them.

Secure lamps and lanterns firmly to the ceiling.

You should know the profession or work activity of your neighbors or co-workers in case you need help.

Organize periodic drills so that each member of the family knows what to do during the earthquake, and ask the internal Civil Protection unit to conduct them in your workplace as well.

Find safe places in each room: under solid tables, sturdy desks, supporting walls or door frames with locks. Reinforce this information by having each family member choose one of these places to protect themselves.

Identify dangerous places in your home to get away from them, such as windows where glass might shatter, bookcases, or other furniture that might fall.

Identify evacuation routes and keep them clear.

During eartquake

Remain calm and stay in the safety zones of the place where you are at the time of the earthquake and try to protect yourself as best as possible by staying where you are. Most of the injuries in an earthquake have occurred when people tried to enter or leave homes or buildings.

Stand under a locked door frame or with your back to a load-bearing wall.

Make a "ball" by hugging yourself in a corner; if possible, protect your head with a cushion or blanket.

Stay away from windows, mirrors, and glass items that can break.

Avoid being under lamps and other hanging objects.

Stay away from bookcases, cabinets, or heavy furniture that could fall or be dropped.

Stay away from stoves, braziers, coffee makers, radiators, or any hot utensils.

If you are in a building, stay where you are; do not try to use the elevators or stairs during the earthquake.

Stay calm.

If you are outside, seek shelter there. Make sure you are safe from wires, poles, trees and branches, outside stairs, buildings with decorated facades, balconies, eaves, fireplaces, flower pots, and any other objects that may fall, especially if you are in an urban area, as well as areas of multi-story buildings whose windows and facades may spread dangerous debris onto the streets.

If you are in your vehicle, drive calmly to a location away from bridges or utility poles and park in an area out of danger.

In crowded, public places (movie theater, theater, subway, stadium, classroom), do not shout, run, or push; exit calmly if the exit is not congested; otherwise, stay in your own seat, placing your arms over your head and lowering it to your knees.

In the case of the Metro or underground transport system, remain calm and follow the instructions of the security personnel. Keep in mind that the structure of the railroad transportation system offers security.

If possible, turn off the gas supply, disconnect the power supply. Avoid lighting matches or any source of the fire.

If you are trapped, remain calm and try to communicate with the outside world by knocking on an object.

Check for injuries and, if necessary, seek medical help.

Do not use the elevators and be cautious with the stairs; they may have been weakened by the earthquakes.

Avoid stepping on or touching any fallen or loose wires.

Carefully check for damage; if serious damage is done to vertical elements (columns and/or load-bearing walls), do not use the building.

Do not light matches, candles, open flame, or electric appliances until you are sure that there are no leaks or problems in the electric or gas installation.

In case of gas or water leaks, report them immediately.

If there are fires, call the fire department or the rescue brigade.

Do not consume food or drink that has been in contact with broken glass, debris, dust, or any contaminant.

Immediately clean up spilled liquids, such as medicines, flammable or toxic materials.

Use the phone only to report an emergency.

Turn on the radio for information and guidance.

When you open cupboards, shelves, or closets, do so carefully because objects may fall on you.

Do not spread rumors or listen to them, because they disorient people.

Follow the instructions given by the authorities or by the relief teams.

Carefully carry out a complete check of your home.

As a measure against any risk, pack your personal documents in advance: birth and marriage certificates, deeds, agricultural documents, passbooks, CURP, etc., in tightly closed plastic bags, stored in backpacks or backpacks that you can carry in such a way that your arms and hands are free.

When leaving, do so with care and order; follow the instructions of the authorities or the relief brigades.

Be prepared for future earthquakes, also called aftershocks. They are usually weaker but can cause additional damage.

Source: National Seismological Service