Mexico was struck by an earthquake of magnitude 5.8 (M5.8) in the early hours of 16 June UTC (11.19 pm on 15 June, local time). The epicentre of the quake, which was initially reported as M6.0, occurred close to the town of Jolapan, just 120 km south of the capital, Mexico City – residents felt the tremor across a large area of central Mexico.
The United States Geological Survey’s Pager alert system suggested that Sunday’s tremor had a statistical likelihood of low levels of economic damage, injuries or possible deaths, but at the time of writing there were no reports of damage or casualties… although some buildings in Mexico City were evacuated as a precaution and there were some power outages.
Mexico’s Tectonic Setting
Located where two of the earth’s tectonic plates meet, Mexico is highly seismically active and vulnerable to repeated earthquakes. The Cocos plate is moving north-eastwards against the north American plate at a rate of around 55-75 mm per year and, being composed of dense oceanic crust is forced beneath the more buoyant continental crust of central America. The friction generated by this downward motion is periodically released in the form of earthquakes, either along the interface between the two plates or within the over-riding plate.
Typically, in a subduction zone setting such as this, earthquakes follow a pattern of increasing depth away from the boundary, reflecting the dip of the subducting slab – the steeper the dip, the narrower the zone in which earthquake epicentres are found. Central Mexico is unusual, however, in that the dip of the downgoing plate it unusually shallow, varying from around 30⁰ in southern Mexico to virtually horizontal further north. (At the southern end of the subduction zone, the dip is as steep as 45-60⁰ according to Yeats, in Active Faults of the World.)
The reasons for this are not fully understood, but it does have implications for the overlying land. As the map of seismicity for Mexico shows, earthquakes are generally shallow (rarely deeper than 300km): and shallow earthquakes are typically more damaging than deeper ones.