Receiver function search for a baby plume in the mantle transition zone beneath the Bohemian Massif

Abstract

SUMMARY The western Bohemian Massif is known for geodynamic phenomena such as earthquake swarms, CO2 dominated free gas emanations of upper-mantle origin, and Tertiary/ Quaternary volcanism. Among other explanations, a small-scale mantle plume has been suggested. We used data from the international passive seismic experiment BOHEMA (2001–2004) and of a previous seismic experiment to investigate the structure of the upper-mantle discontinuities at 410km and 660km depth (the ‘410’ and the ‘660’) beneath the Bohemian Massif with the P receiver function method. More than 4500 high-quality receiver function traces could be utilized. Two stacking techniques were used: stacking by station (common station method, CSM) and stacking by piercing points in the mantle transition zone (common conversion point method, CCM).Sincethestationspacingisveryclose,raysfromdifferentstationshavesimilarpiercing points in the mantle transition zone. Therefore CCM is sensitive in the transition zone and CSM issensitive totheuppermost structureof themantle. TheCSM showsdelayed conversion times from the 410km discontinuity beneath the western Bohemia earthquake region, which indicate a slow uppermost mantle. When stacking our data by CCM, we observe thickening of the transition zone towards the Alpine foreland, which agrees with tomographic results by Piromallo and Morelli. The thickness of the mantle transition zone beneath the western Bohemian Massif is normal, with a faint hint to thinning in the northern part. Ourconclusionisthataplume-likestructuremayexistintheuppermantlebelowthewestern Bohemia earthquake region, but with no or only weak imprint on the 410km discontinuity.