Regarding Fuji, Ukawa (2005) notes, 'On the basis of the DLF earthquake observations by the NIED seismic network, we investigated the temporal change of their occurrence rate from 1980 to 2003 and the hypocenter locations from 1987 to May 2001.

The wave energy increased to approximately twice the average recorded during the prior years. In total, 286 events were identified during the eight months from October 2000 to May 2001. The sharp increase in 2000-2001 is far larger than the increase due to the enlarged seismic network. The cumulative number rate, or the slope of the curve, is almost constant between 1980-1995, followed by several small slope changes before the later months of 2000 due to the improvements in the seismic network and the new data processing system. The cumulative occurrence of DLF earthquakes their associated cumulative wave energy are plotted in figure FUJ2. The typical activity here since the early 1980s was 10-20 earthquakes a year at midcrustal depth described as burst-like activity lasting from several minutes to 30 minutes. Ukawa (2005) examined the 2000-2001 DLF swarm beneath Fuji. Note new instruments and processing accounted for some of the increase seen in 2000-2001 (right of the vertical line), however there was a clear marked increase in events there. Cumulative number of DLF events (dotted curve) at Fuji during 1980-2004 and their cumulative wave energy (solid line). In April 1995, Mt Fuji seismic data recording began using the constellation of stations.įigure 3. Later refinements included adding stations SSN and SHJ (not shown), and in the 1990s, stations, FJN, FJY, FJS and FJH, each with three component seismometers and two component tiltmeters at the bottom of 200-m-deep boreholes. During the early 1980s, the National Research Institute for Earth Science and Disaster Prevention (NIED) installed the Kanto-Tokai seismic network in central Japan (figure 2). Although they concluded that preexisting faults could rupture the chamber walls, the changes were seemingly insufficient to do so, suggesting no eruption was imminent.īackground. Fujita and others (2013) assessed the possibility that the stress-field and pressure changes could enable magma to escape to the surface. In addition, an M W 5.9 aftershock was centered below Fuji. The next section reports the stress-field and pressure changes to Fuji's magmatic system due to the 11 March 2011 Tohoko megathrust, an M W 9 earthquake, which created the tsunami that devastated parts of costal NE Honshu including the Fukushima nuclear power plant. Discussion in those papers noted likely molten material at depth below the volcano. In the first section below, we summarize work by Ukawa (2005) and Nakashimi and others (2004) who provide further details and analysis of DLF swarm activity, and discuss midcrustal, low-frequency earthquakes (MLFs) recorded during 1998-2003. Our previous reports of February 2001 ( BGVN 26:02) and September 2001 ( BGVN 26:09) described the 2000-2001 deep low-frequency (DLF) earthquake swarm under Fuji. Fujita and others (2013) investigate the likelihood that Fuji may erupt due to the 2011 E Shizuoka earthquake (M 6) centered on the volcano.

2000-2001 epicenter migration deep magma 2011 M 6 aftershock at volcanoįuji remains non-eruptive.

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