Spatial distribution of crack structure in the focal area of a volcanic earthquake swarm at the Hakone volcano, Japan

abstract The Kolomogorov model of event occurrence as developed by Knopoff in earthquake model studies has been applied to a volcanic earthquake swarm. It is shown that in this case, where the rate of seismic energy release was nearly constant in time, the model adequately relates the various seismicity statistics of the swarm.

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The Volcanic Earthquake Swarm of October 20, 2009 in the Tatun Area of Northern Taiwan

Terrestrial Atmospheric and Oceanic Sciences ◽

10.3319/tao.2014.04.11.02(t) ◽

2014 ◽

Vol 25 (5) ◽

pp. 625 ◽

Cited By ~ 14

Author(s):

Hsin-Chieh Pu ◽

Cheng-Horng Lin ◽

Yu-Chih Huang ◽

Li-Chin Chang ◽

Hsiao-Fen Lee ◽

...

Keyword(s):

Earthquake Swarm ◽

Volcanic Earthquake ◽

Northern Taiwan

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Statistical analysis of tidal effect on non-volcanic earthquake swarm activity in Wakayama Prefecture, southwest Japan

10.5194/egusphere-egu21-13890 ◽

2021 ◽

Author(s):

Kazuki Machida ◽

Hiroyuki Nagahama ◽

Jun Muto

Keyword(s):

Normal Stress ◽

Earthquake Swarm ◽

Tohoku Earthquake ◽

Rate Variation ◽

Volcanic Earthquake ◽

Seismicity Rate ◽

Tidal Forces ◽

Tidal Triggering ◽

Tidal Stress ◽

Swarm Activity

Earthquakes occur when the fault stress accumulates to the critical level. External forces such as tidal forces may contributes to the triggering of earthquakes reaching the critical state. For example, in the case of 2011 Tohoku Earthquake, it is reported that there is a correlation between tidal forces and the earthquakes prior to the mainshock. Earthquakes with smaller magnitude are also affected by tidal forces and expected to show correlation with tidal forces.Tidal triggering of non-volcanic seismic swarm has not been well documented. So, we choose the Wakayama Prefecture as a targeting region. The cause of the earthquakes occurring in the region is considered to be the presence of the water below the seismogenic depth. The swarm activity continues from 1980s. We analyzed the shallow earthquakes in the northern part of Wakayama Prefecture from 1998 to 2016. We used statistical method called Schuster test to analyze correlation between earthquakes and tidal stress.The result of the analysis shows that the earthquakes have a correlation with tidal forces which have the periodicity near the half of the lunar day and the amplitude of the seismicity-rate variation is about 16% of the average earthquake frequency. Correlation between the earthquakes and tidal forces is stronger at the periods when larger number of earthquakes occur. From tidal stress calculation, it is found that both solid tide and oceanic tide are important at this region. This study confirms that most of the earthquakes larger than Mw 4 in the region occur in the rising period of tidal normal stress or just after the maximum of tidal normal stress. Therefore, tidal observation gives information about the criticality of rocks and temporal heterogeneity of the earthquake occurrence.

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GNSS Observation and Monitoring of the Hakone Volcano and the 2015 Unrest

Journal of Disaster Research ◽

10.20965/jdr.2018.p0526 ◽

2018 ◽

Vol 13 (3) ◽

pp. 526-534 ◽

Cited By ~ 1

Author(s):

Ryosuke Doke ◽

Masatake Harada ◽

Kazuki Miyaoka ◽

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Keyword(s):

Crustal Deformation ◽

Hot Springs ◽

Displacement Vector ◽

Earthquake Swarm ◽

Satellite System ◽

Volcanic Edifice ◽

Hakone Volcano ◽

Western Area ◽

Kanagawa Prefecture ◽

Volcanic Activities

In recent years, earthquake swarm activities have occurred at the Hakone Volcano in the western area of Kanagawa Prefecture, Japan, with a frequency of once in several years. Global Navigation Satellite System (GNSS) observations have detected the inflation of volcanic edifice during these activities. Hot Springs Research Institute of Kanagawa Prefecture (HSRI) regularly observes crustal deformation for monitoring seismic and volcanic activities by using 16 sites of GNSS observation, which were installed in the western area of Kanagawa Prefecture. These observed data, together with those from other agencies, are analyzed routinely, and time-series graphs, displacement vector diagrams, and strain maps are illustrated to monitor seismic and volcanic activities. Given that GNSS monitoring detected the baseline extension about half a month or a month before the earthquake swarm activities, a stacking analysis is routinely performed for early detection of the extension. Some of the analysis results can be found on the website of HSRI. The Hakone Volcano had the largest earthquake swarm activity beginning at the end of April 2015, and a phreatic eruption occurred in Owakudani at the end of June 2015. The GNSS observed crustal deformation, which indicated the inflation of the volcanic edifice in early April 2015. This inflation can be explained by a volume change of a point pressure source located about 6.5 km below sea level.

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Electrical resistivity variation connected to volcanic earthquake in the Campi Flegrei, Italy

10.5194/egusphere-egu2020-18692 ◽

2020 ◽

Author(s):

daniela tarallo ◽

Giuseppe Cavuoto ◽

Vincenzo Di Fiore ◽

Nicola Pelosi ◽

Michele Punzo ◽

...

Keyword(s):

Electrical Resistivity ◽

Earthquake Swarm ◽

Fluid Pressure ◽

Source Area ◽

Campi Flegrei ◽

Present Observation ◽

Volcanic Earthquake ◽

Resistivity Variation ◽

Pressurized Fluids ◽

Fluid Pressurization

In this study we show an 2D Electrical Resistivity Tomography (ERT) survey acquired in Agnano site pre (Dec 5th, 2019) and post (Dec 12th, 2019) earthquake events occurred in Pisciarelli-Solfatara areas. This earthquake swarm consisted of sequence of 34 earthquakes with Magnitude (Md) -1.1&#8804;Md&#8804;2.8 at depths between 0.9 and 2.3 km. In particular, the earthquake of Dec 06th, 2019 at 00:17 UTC with Md = 2.8 (depth 2 km) was the maximum recorded event since bradyseismic crisis began in 2005.The ERT survey allow us to identify the main structural boundaries (and their associated fluid circulations) defining the shallow architecture of the Agnano volcano. The hydrothermal system is identified by very low values of the electrical resistivity (<20 &#937; m). Its downwards extension is clearly limited by the lava and pyroclastic fragments, which are relatively resistive (>100 &#937; m). The resistivity values are increased after the main shock. This increase in resistivity may have been caused by a change in the state of stress and a decrease in pore pressure (subsequent depressurization). Previously to the earthquake, an increase in pressurized fluids has been observed which have reduced the resistivity values. The present observation suggests that the temporal variation of the resistivity values is related to the variation of the pore fluid pressure in the source area of the swarm, facilitated by earthquake and the subsequent fluid diffusion. The combination of these qualitative results with structural analysis leads to a synthetic model of magmatic and hydrothermal fluids circulation inside the Agnano area, which may be useful for the assessment of potential hazards associated with a renewal of fluid pressurization, and a possibly associated partial flank-failure.

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