********************************************************** From: H.Rymer <H.Rymer@xxxxxxxxxx> ********************************************************** 6.2 magnitude earthquake near the Poás Volcano: rockfall and landslides within the active crater and intensification of fumarolic activity Heredia, 8th and 9th January 2009 A strong earthquake affected Costa Rica the 8th of January 2009 at 1:21 p.m. The seismic event was located 10 km to the east of Poás Volcano, at 6 km of depth and with a magnitude of 6.2 on the Richter scale by the OVSICORI-UNA network of seismometers. The USGS, citing sources of the Universidad de Costa Rica, reports a depth of 4.5 km below the surface. Over 1500 aftershocks were recorded after the earthquake until 10:00 p.m. of January the 9th. A precursory seismic event was recorded in the same area with a magnitude of 4.0 in the Richter Scale on 7th of January at 10:10 a.m. The earthquakes are considered to be related to the known fault system in the region to the east of Poás Volcano (see figures 1a and 1b). Personnel from the Volcano Monitoring Program of OVSICORI-UNA and scientists from the Open University (United Kingdom), who were performing geophysical measurements at the crater of Poás Volcano at 1:21 p.m. when the earthquake occurred, reported several aftershocks and watched numerous landslides and rockfalls from the inner walls around the active crater of Poás volcano (see figures 2 and 3), and also in the North sector of the main crater (Von Frantzius, see Figure 4), as a result of the seismic activity. New fractures opened up along the eastern part of the rim. The scientists also observed an increase in the level of fumarolic activity on the pyroclastic dome to the South of the acid lake within the active crater. On 13th January aftershocks were continuing, some of which were felt. There was a small phreatic eruption in the active crater lake at about 2:30PM. Personnel from OVSICORI-UNA and OU are studying and evaluating the consequences of the events and have intensified their monitoring efforts in the area. More information on Poás Volcano and the earthquakes of 7th and 8th of January 2009 is available from the OVSICORI website: www.ovsicori.una.ac.cr <http://www.ovsicori.una.ac.cr> , or directly from the OVSICORI-UNA personnel, phone number: (00506) 2-562-4001, fax (00506) 2-261-0303. Also at http://cepsar.open.ac.uk/ in news item dated 12 January 2009. Report by: Lic. Jorge Brenes Marín. Volcanic Seismology OVSICORI-UNA. Dr. Rodrigo del Potro. Volcanology OVSICORI-UNA. MSc. Víctor González. Seismology OVSICORI-UNA. Bach. Walter Jiménez. Seismology OVSICORI-UNA. Lic. Tomás Marino. Volcanology OVSICORI-UNA. Dr. María Martínez Cruz. Geochemistry, Volcanology OVSICORI-UNA. Lic. Juan Segura Torres. Seismology OVSICORI-UNA. Lic. Rodolfo van der Laat. Volcanology OVSICORI-UNA. Floribeth Vega Solano, Seismology OVSICORI-UNA. Dr Hazel Rymer. Open University, UK Melanie Hinrichs Open University, UK Beatriz Gomez Izquierdo. Open University, UK Guillermo Caravates. Open University, UK ============================================================== To unsubscribe from the volcano list, send the message: signoff volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxxx To contribute to the volcano list, send your message to: volcano@xxxxxxxx Please do not send attachments. ==============================================================
