We do sit on the Rio Grande rift so earthquakes in Central NM are fairly common. Recent activity has been heard and felt by the Socorro residents ever since the 3.2 quake on August 19th. The rift is seperating and this means we are seeing the earth below the Rio Grande going in two different directions. When the two plates rub against each other your get a tremor or earthquake.
Seismicity within the Socorro region has been very active in recent days. A felt earthquake of magnitude (ML) 2.3 occurred on August 19, 2009 approximately 3 km NE of Socorro near Escondida. Small events continued to occur during this time with activity beginning near the Lemitar area on August 24, 2009. These events have been numerous and fairly shallow depth of 5.5-6 km. The largest event was ML=2.5 on August 29, 2009 at 18:31:01 MDT (August 30, 2009 at 01:31:01 UTC) and was felt by many residents of Lemitar and Socorro. We have preliminary locations on the largest 53 events (ML range of 0.5 to 2.5); however, many smaller events have also occurred since August 19, 2009. The locations of 53 of the largest earthquakes are very similar, suggesting that this is an earthquake swarm. Earthquake swarms are usually caused in response to tectonic or hydrological pressure changes in the crust. Minor felt earthquakes in this region are not uncommon, and have been documented by Dr. Allan Sanford in the past (Figure below, blue squares). However, this is the longest-lasting earthquake activity in this area in the last several years.
