Publication Date:
2015-04-04
Description:
Mt. Fuji has ejected a huge amount of basaltic products during the last 100,000 years. Even though the region around Mt. Fuji is tectonically active, the seismicity below Mt. Fuji is low, resulting in little knowledge about the seismic structure there. To gain more insight into the magma-plumbing system, we obtain the seismic structure beneath Mt. Fuji by the receiver function (RF) technique. RFs at seismic stations around Mt. Fuji show positive phases at ~3 and ~6 seconds, representing the conversion of P to S waves at a positive velocity boundary in the Philippine Sea (PHS) plate. Cross sections of RF amplitudes reveal two distinct velocity boundaries around Mt. Fuji, at depths of 40–50 km and 20–30 km, which we interpret to be the boundary between the crust-mantle transition layer (CMTL) and the uppermost mantle of the Izu-Bonin arc (IBA) and the velocity discontinuity just below the region where low- frequency earthquakes (LFEs) of Mt. Fuji have occurred, respectively. The velocity boundary at about 50-km depth shows a clear gap just beneath Mt. Fuji. We suggest that this gap represents a weaker velocity contrast zone through which the magma of Mt. Fuji ascends from the Pacific (PAC) plate. A thorough grid search reveals that a low-velocity zone at depths of ~13–26 km explains all the characteristics of RFs around Mt. Fuji, leading us to interpret the high velocity boundary just below the LFE region as the lower boundary of Mt. Fuji's magma chamber.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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