Volcanic Earthquakes and Tremors Associated with the 2000 Miyakejima Volcano Eruption.

The 2000 Miyakejima volcano activities started on Jun. 26 after 17 years of quiescence. The NIED Miyakejima volcano observational network, mainly equipped with seismometers and tiltmeters, successfully and continuously detected the migrations of magma. The volcanic activities consist of four stages : the dike intrusion (Stage 1 : Jun. 26-27), the subsidence of volcanic body (Stage 2 : Jun. 27-Jul. 8), tilt-steps and successive collapses of the summit crater (Stage 3 : Jul. 8-Aug. 18), and the subsidence of volcanic body and episodic eruptions (Stage 4 : Aug. 18-). This paper summarizes characteristic seismic phenomena that occurred at each stage; i.e., VT (volcanotectonic) earthquakes, LP (long-period) earthquakes, and volcanic tremor. Significant phenomena are the 50-second pulse waves associated with the tilt-steps at Stage 3. They reflect subsurface magmatic processes and their temporal and spatial variations.