An investigation on micro earthquakes at the Torfajokull volcano, south Iceland
Speaker: Pan Cheng-Yu
Abstract
Torfajokull is a large rhyolitic volcanic edifice with a 12-km-diameter caldera and abundant high temperature geothermal activity. It is located in the neovolcanic zone in south Iceland, at the junction of the eastern rift zone and a transform zone with the intraplate volcanic flank zone of south Iceland. The latest eruption at Torfajokull occurred about 500 years ago. Torfajokull is a source of persistent small-scale seismicity, where two types of earthquakes occur. High-frequency events are concentrated in the western part of the caldera and low-frequency events cluster in the south. To study this microseismicity in detail, a temporary array of 20 broad-band seismic stations was deployed between 2002 June and November. These temporary stations were embedded in the permanent South Iceland Lowland (SIL) network and data from nine adjacent SIL stations were included in this study. A minimum one-dimensional (1-D) velocity model with station corrections was computed for earthquake relocation. High- and low-frequency earthquakes from the Torfajokull volcanic were then relocated calculating a non-linear, probabilistic solution to the earthquake location problem. High-frequency earthquakes are mainly located beneath the caldera with hypocentres between 1 and 6 km depth and lie almost exclusively within the geothermal system. A sharp cut-off in seismicity at 3 km suggests either that there is a marked temperature increase or that this is a structural boundary. The low-frequency earthquakes are located in the southern part of the caldera, between two small glaciers. Areas of intensive geothermal activity surround the cluster of low-frequency events. It is argued that these earthquakes are associated with active magma in the south part of the Torfajokull caldera, possibly a rising cryptodome.
Reference
Lippitsch, R., White, R., Soosalu, H., 2005. Precise hypocentre relocation of microearthquakes in a high-temperature geothermal field: the Torfajokull central volcano, Iceland, Geophys. J. Int. (2005) 160, 370–387 doi: 10.1111/j.1365-246X.2005.02467.
Soosalu, H., Lippitsch, R., Einarsson, P., 2006. Low-frequency earthquakes at the Torfajokull volcano, south Iceland, J. Volcanol. Geotherm. Res. 153 (2006) 187 – 199 doi:10.1016/j.jvolgeores.2005.10.012.