Seismicity of poás volcano, Costa Rica

Abstract

This chapter summarizes the results of previous studies on the seismicity of Poás volcano and shows its behavior from 1980 to 2006, the last year of analogical recording at the seismic station of the Red Sismológica Nacional (RSN: ICE-UCR) located on the summit of the volcano. A new estimate of the signal frequency for those events occurring between 2007 and 2015 is also shown. The overview is based on the need to understand and classify the seismic signals of the Poás volcano according to the available records, modern instrumentations, and current knowledge about volcanic seismology. This will help to improve the management of volcanic emergencies and interpret changes in seismic activity in the volcano. To carry out the work, we first revised previous publications related to the seismicity of Poás volcano. Then, we analyzed seismic records of the seismic station VPS2 of the Red Sismológica Nacional (RSN: ICE-UCR) and other data generated by temporary seismic networks that were installed in the volcano. Three seismic signals have been clearly identified at Poás volcano: low-frequency events, tremors, and tectonic earthquakes. The most typical ones are low-frequency signals. The low-frequency events occur inside and around the main crater, at shallow depths, in response to vapor pressure. Tremors sporadically occur at Poás before and during the period of perturbation inside the volcano as a consequence of degassing. Swarms of small tectonic earthquakes (frequency = 1–2.5 Hz) also occur within the volcanic area in response to movements in local faults. The seismicity of Poás volcano, especially the low-frequency ones, increases before each eruptive cycle.