A couple of days ago we witnessed a series of pyroclastic flows, and this morning it was an earthquake. I was out on the deck of the cabins. The cabins are on stilts but stand firm against the worst wind and rain that Costa Rica can throw at them. However, the structure had what could be described as an unnatural quiver - almost as if the wind had caught it in an unusual way. Except there was no wind.
Others felt it and after breakfast I checked online. The USGS are recording a Mag.4.8 earthquake at 9.894N 85.272W 46.7km deep, "Coast of Costa Rica" (actually locating it just on the Nicoya Peninsula). OVSICORI are giving it a slightly higher energy of 5.1. The differences are probably due to different equipment locations. Also the USGS calculation will be fully automated and as it is only a moderate non-US earthquake, it probably hasn't been examined by a human.
The coastal location means it is NOT an Arenal earthquake but an earthquake related to subduction of the Pacific Plate under the Caribbean plate. The depth is consistent with this - it is too deep for a volcano, and most earthquakes of this depth are related to subduction.
Here's the seismogram recorded by the OVSICORI Volcan Arenal seismometer (VACR):
The earthquake is the largest squiggle just after 6:45am local time. The seismometer even goes off scale. It is only a moderate sized earthquake but we are fairly close, and the seismometer is set to detect vertical motions (the dominant kind in a thrust fault - which is the most likely for a subduction zone).
Others felt it and after breakfast I checked online. The USGS are recording a Mag.4.8 earthquake at 9.894N 85.272W 46.7km deep, "Coast of Costa Rica" (actually locating it just on the Nicoya Peninsula). OVSICORI are giving it a slightly higher energy of 5.1. The differences are probably due to different equipment locations. Also the USGS calculation will be fully automated and as it is only a moderate non-US earthquake, it probably hasn't been examined by a human.
The coastal location means it is NOT an Arenal earthquake but an earthquake related to subduction of the Pacific Plate under the Caribbean plate. The depth is consistent with this - it is too deep for a volcano, and most earthquakes of this depth are related to subduction.
Here's the seismogram recorded by the OVSICORI Volcan Arenal seismometer (VACR):
The earthquake is the largest squiggle just after 6:45am local time. The seismometer even goes off scale. It is only a moderate sized earthquake but we are fairly close, and the seismometer is set to detect vertical motions (the dominant kind in a thrust fault - which is the most likely for a subduction zone).
