Intense crustal activity including earthquake swarms, eruptions, and a caldera formation in the northern Izu Islands started on June 26, 2000. GEONET data reveals the spatial pattern and time evolution of ground deformation. The observations reveal shrinking and subsidence of Miyakejima and extension between Kouzushima and Niijima (Fig.1). The crustal deformation pattern are explained by several sources consist of a deflation source (0.12km^3) beneath Miyakejima, tensile faults (1.04km^3) located between Miyakejima and Kouzushima, and several shear faults. Mass balance considerations suggest that a large amount of magma migrated 30km from Miyakejima toward Kouzushima.
Figure 1. Horizontal displacements at GEONET GPS stations during the period from June 13-22 to August 27-31.
Stars show epicenters of the 5 largest earthquakes (Mjma>=6.0) [after Nishimura et. al., 2001, GRL, 28, 3745-3748].
Copyright 2004 Geography & Crustal Dynamics Research Center.
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