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Increased seismicity at San Miguel volcano (Chaparrastique), El Salvador 7 July 2009

Posted by admin in activity reports, El Salvador, San Miguel.
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San Miguel volcano, also known locally as Chaparrastique, is situated in the east of El Salvador and is a mere 15 km away from the city of San Miguel (population more than 200,000). It is one of El Salvador’s most active volcanoes, with a record of frequent eruptions since the early sixteenth century.

There are now reports of increased seismic activity, in the form of microquakes, at the volcano. The Salvadorean geological service, the Servicio Nacional de Estudios Territoriales (SNET), reports in a special bulletin that there has been an ‘increase in microseismicity [microsismicidad] at Chaparrastique volcano beginning at 03:00 on 6 July 2009′ which is reflected in the RSAM signal which has been fluctuating at 700-1300 units, well above the normal hourly average of 30-50 units RSAM. Such ‘microseismicity’ has been associated in the past with other manifestations of volcanic activity, and is caused by the heating of water within the volcano. The SNET bulletin explains:

The microseismicity is associated with the pressure of [water] vapour which causes the volcanic structure to vibrate, and which is caused by the heating and evaporation of rainwater which infiltrates and moves through the strata of the volcano, increasing its internal pressure.

A 2-kilometre-radius ‘security zone’ has been imposed around the volcano, with local residents and tourists being advised to keep away while monitoring of the volcano continues.

News
Reportan major actividad del volcán de San MiguelEl Diario del Hoy, 6 July 2009
Volcán sube los niveles de actividadEl Diario del Hoy, 6 July 2009
Volcán Chaparrastique de El Salvador incrementa su actividad microsísmica – Terra.com, 7 July 2009
Vigilan volcán salvadoreño por actividad microsísmica – Univisión, 7 July 2009

Information
Global Volcanism Program: San Miguel – summary information for San Miguel/Chaparristique (1403-10=)
Servicio Nacional de Estudios Territoriales (SNET) – Salvadorean national geological service

The Volcanism Blog