The month was a bit more than nine hours old when a sharp shock rattled much of the country.
The quake, estimated at a magnitude of 4.2, was inland and 11 kilometers north of Quepos, according to the Observatorio Vulcanológico y Sismológico de Costa Rica. It was yet another result of the lighter Caribbean tectonic plate moving over the Coco plate, the observatory said.
The time was put at 9:07 a.m.
The observatory credited deformation of the Coco plate as the reason for two significant quakes in May. One was the May 13 event far below Puriscal that was felt all over the country.
The observatory put the magnitude at 5.9. Other observers said 6.0.
The second quake was at 2:37 a.m. May 21 about 8 kilometers southwest of San Vito de Coto Brus in southern Costa Rica. That was only 14 kilometers deep, far shallower than the 69 kilometer depth of the May 13 quake.
In none of the three quakes was any serious damage reported.