Eibl, Eva P. S.Eva P. S.EiblBean, Christopher J.Christopher J.BeanVogfjörð, KristínKristínVogfjörðBraiden, AoifeAoifeBraiden2015-01-122015-01-122014 Elsev2014-12-01Journal of Volcanology and Geothermal Researchhttp://hdl.handle.net/10197/6281Hekla is one of Iceland's most active volcanoes. Since 1970 it has erupted four times with a period of quiescence of 14 years since the last eruption. We detected persistent levels of background microseismicity with a temporary seismic network in autumn 2012. An amplitude based as well as an arrival-time based location method was applied to two populations of events and located them at shallow depths on the northern flank, close to the summit. This seismicity has not been identified previously by the permanent seismic network in Iceland as it is below its detection threshold. The detected events were either short, higher frequency events with distinct arrivals located beneath the summit on the northern flank of Hekla or longer, emergent, lower frequency events about 4 km northeast of the summit at 200¿400 m depth below the surface. Estimated moment magnitudes were MW = -1.1 to -0.1 and MW = -0.9 to -0.0 and local magnitudes ML = -0.5 to +0.3 and ML = -0.3 to +0.3, respectively. This seismicity does not show any correlation with gas output but is located at the steepest slopes of the edifice. Hence we suggest that the current shallow microseismicity at Hekla is structurally controlled. This offers a possible opportunity of using near summit microseismicity as a tool for monitoring emerging unrest at Hekla. Microseismicity rates will be very sensitive to small stress perturbations due to magma migration at depth. Currently in the absence of microseismicity monitoring, Hekla switches from apparently quiescent to fully eruptive on the order of only 1 h.enThis is the author’s version of a work that was accepted for publication in Journal of Volcanology and Geothermal Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Volcanology and Geothermal Research (VOL 289, ISSUE#, (2014)) DOI: 10.1016/j.jvolgeores.2014.11.004HeklaIcelandShallow seismicityVolcano seismologyMicroseismicityEarthquakeJournal Article28922423710.1016/j.jvolgeores.2014.11.0042015-01-07https://creativecommons.org/licenses/by-nc-nd/3.0/ie/