Aftershock to Mexico’s March Earthquake Reaches M6.0

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Earthquake depth increases away from the plate boundary (Image from USGS)

Causes of Mexico’s Quakes

The pattern of the recent earthquake swarms in Mexico is consistent with subduction zone earthquakes. Along Mexico’s Pacific coast, the eastern edge of the Cocos Plate abuts the North American and Caribbean plates. The relative plate movements force the denser Cocos Plate downwards where it is eventually subsumed beneath the other two. It is along this plate boundary that the recent swarm of earthquakes has occurred.

The downwards movement of the Cocos Plate creates a plane along which friction occurs and where, when rocks fail, earthquakes occur. This plane is large, comprising the area of subduction along the length of the boundary and also extending deep into the earth. Typically, rock failure can take place – and an earthquake occur – anywhere along this plane. The situation in Mexico is complicated by the juxtaposition of three plates, and the recent series of earthquakes has occurred close to a transform fault, where lateral movement occurs, as well as in association with subduction.

Mexico Earthquakes

The pattern of seismicity for Mexico clearly shows the depth of earthquakes increasing from the coast inland up to depths of 150-300 km (some other subduction zones show earthquakes up to depths of 800km) and from this is possible to envisage the angle and extent of the subducting slab beneath the country.

The shallow depths recorded for the recent series of shocks are typical of Mexican earthquakes, which do not reach the depths which are seen elsewhere, and their closeness in spatial and temporal terms suggests, though it does not conclusively prove, that they are all associated with the same general shift in the subducting plate.

Sources

USGS. Historic earthquakes list. Accessed 3 April 2012

USGS. Recent earthquakes list Magnitude 6.0 – Oaxaca, Mexico. Accessed April 3, 2012.

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