Late last night, southern Mexico was hit by an earthquake that occurred offshore near the border with Guatemala. According to the USGS, the earthquake was within the Cocos Plate and was at a depth of ~70 km. In this region, the Cocos Plate is subducting beneath the North American Plate. This was an unusual earthquake for this tectonic setting given its depth and the way the earth ruptured. Typically, earthquakes in subduction zones are caused by compression of two plates colliding and they usually occur at shallow depths. The seismic waves from this earthquake show that the earth was extending during the earthquake and that this earthquake happened at a relatively deep depth. This earthquake will keep seismologists busy for a while.