The center of destruction, was it from old buildings, or not well built? Seems like the out lying areas weren't as badly affected. Such a strong quake would seem like it would have flattened a larger area.
The center of the city was mostly office buildings. Portoviejo is a valley and according to a few experts the earth in the zone was mostly sediments from the river and it liquified during the quake. You can also see a line of dots in the west. All those houses fell into the river.