A week in which several major earthquakes occurred around the Pacific rim ended with a major event of magnitude 7.2 shaking the Guerrero province of Mexico on the morning of Good Friday, 18 April.
According to data from the United States Geological Survey, the tremor occurred near the coast around 270km south west of the capital, Mexico City, at a depth of around 14km.
At the time of writing news media were reporting only minor damage and injuries; but the shaking from the event was intense in the immediate area and the USGS Pager program indicated there was a high chance of fatalities (a 43% probability of between 10 and 100 deaths).
The onshore location of the epicentre, however, meant that despite its magnitude the earthquake didn’t generate a tsunami.
Mexico Good Friday Earthquake:
The Tectonic Setting
The coastal zone of Mexico, like that of the rest of the western coasts of the Americas, is highly seismically active. The convergence of (in this case) the Cocos plate and the North American plate creates a subduction zone with the former, which is is of relatively dense oceanic crust, dipping beneath the latter.
No detailed information is yet available about the source of the tremor, although there are clues in the initial data.
The depth, at 14km, is relatively shallow, and the epicentre at some distance from the plate boundary, which in many cases would imply that the faulting occurred within the over-riding plate. In this case, however, the angle of subduction is unusually shallow and a look at a detailed map of the area leaves open the possibility that the earthquake did, indeed, occur at or close to the plate interface.
Seismic History and the Guerrero Seismic Gap
The convergent movement means that Mexico is highly earthquake prone: since 1900 the country has been struck around 50 times by earthquakes of at least M7.0.
The majority of these earthquakes occurred along the coastal zone. Fifteen were larger than the Good Friday 2014 tremor, and three of them (two in 1995 and one in 1985) were of M8.0.
Nevertheless, although the area is so vulnerable to earthquakes,seismologists had identified an area of limited movement, know as a seismic gap, along this part of the margin.
Yeats noted that this gap lies between 100 and 101 degrees longitude – exactly the stretch of coast in which the earthquake struck. In fact, however, although the Good Friday earthquake was the largest to strike in this gap since 1909, there have been other major earthquakes very close to it so that in this instance the concept of the seismic gap is of more relevance to seismologists than t local residents – who are used to finding the earth shake.
Good Friday Quake
Despite the minor reported damage, and the lack of a tsunami, the intense shaking could be responsible for injuries. Did you feel this tremor? How strong was it in your area?