The probability of an earthquake occurring on the same day and 32 years apart is 5% in a country like Mexico, where there is an average of two powerful earthquakes per year with a magnitude higher than 7 on the Richter scale.
“We estimate that the probabilities are 5%, although we would have to qualify several assumptions,” Vala Hjorleifsdottir, an Icelandic researcher at the Institute of Geophysics of the National Autonomous University of Mexico (UNAM), told Efe.
The emotional impact of the strong earthquake last Tuesday that shook central Mexico was added to the fact that it was the 32nd anniversary of the destructive earthquake of September 19, 1985 that was left in the memory of the residents of the capital as a great disaster, since about 20,000 people died.
What probability is there then that a strong earthquake occurs the same day with 32 years of difference?
To explain this probability, the researcher takes as a starting point the premise that in Mexico, an average of two earthquakes occurs larger than a magnitude 7 on the Richter scale, so every day “there is a probability of 1 in 730”.
He adds that if one considers any day it turns out that the probability of a strong tremor “is not very high”, but that it is increased when taking into account the many years that have passed since the happened the 19 of September of 1985.
“If all the odds of all the years that in one of the 32 years have passed a big event on September 19, we reach the 5% probability, 1 in 20,” explains the researcher, seven years old in high school.
Regarding the possibility of another major earthquake occurring sometime in the future, he says it is “clear that it can happen and with the same probability of 5%.”
Hjorleifsdottir admits that these probabilities start from “very small numbers” because the (historical) statistics are not well known, although he specifies that in the last 100 years more than 50 earthquakes of magnitude 7 and greater have been registered.
As a benchmark, for comparison, the Icelandic researcher points out to a motorist that if he drives little the possibility of accident is less to handle every day.
Beyond the odds that a major earthquake happened on September 19, 32 years apart, seismic events have many differences in their epicenter and the distance of the most affected area.
The 19 of September of 1985 happened at 7.19 local time (13.19 GMT) with a magnitude of 8.2 Richter and with epicenter in the state of Guerrero and left more than 20,000 dead, the greater part in the Mexican capital.
The incident occurred on September 19 at 13:14 local time (6.30 GMT) with epicenter in the states of Puebla and Morelos, and has left a provisional balance of 295 fatalities, according to the most recent report of the authorities.
Another tremor returned today, Saturday, to shake the center and south of Mexico with a magnitude 6.1 on the Richter scale.
The quake was recorded at 07:53 local time (12:53 GMT) and its epicenter was located 7 kilometers west of Union Hidalgo, in the southern state of Oaxaca, the same area where on September 7 an earthquake of 8.2 , the most powerful since 1932, caused 98 deaths.
All this succession of earthquakes is explained, according to the director of the SMN, Xyoli Pérez Campos, because Mexico “is in a complicated tectonic context” by the interaction of five tectonic plates, those of Cocos, North America, Pacific, Rivera and Caribbean.
These plates are segments of the earth’s crust, which they divide like a puzzle, whose interaction when moving on a slimy and viscous mantle is one of the main causes of earthquakes.
During the 20th century, there were 100 earthquakes of magnitude magnitude 7 or greater in Mexico, and since 2000, the National Seismological has reported nine earthquakes of magnitude Richter 7 or greater, the strongest on last September 7 .