Three‐dimensional <i>P</i>‐wave velocity structure of Iwate volcano, Japan from active seismic survey

Tanaka, Satoru; Hamaguchi, Hiroyuki; Nishimura, Takeshi; Yamawaki, T.; Ueki, Sadato; Nakamichi, Haruhisa; Tsutsui, Tomoki; Miyamachi, Hiroki; Matsuwo, Norimichi; Oikawa, Jun; Ohminato, Takao; Miyaoka, Kazuki; Onizawa, Shin’ya; Mori, Takehiko; Aizawa, Katsuo

doi:10.1029/2002gl014983

Cited by 41 publications

(28 citation statements)

References 12 publications

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“…3), assuming a Poisson ratio of 0.25. For depths above sea level, we used a P-wave velocity structure determined by seismic surveys at other active volcanoes in Japan because the velocity structure of Mount Ontake has not been previously investigated (e.g., Tanaka et al 2002;Aoki et al 2009). For the deeper velocity structure, we used a regional velocity model for central Japan based on Ikami et al (1986) and Kato et al (2007).…”

Section: Relocation Of Template Earthquakesmentioning

confidence: 99%

Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan

et al. 2015

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We analyzed seismicity linked to the 2014 phreatic eruption of Mount Ontake, Japan, on 27 September 2014. We first relocated shallow volcano tectonic (VT) earthquakes and long-period (LP) events from August to September 2014. By applying a matched-filter technique to continuous waveforms using these relocated earthquakes, we detected numerous additional micro-earthquakes beneath the craters. The relocated VT earthquakes aligned on a near-vertical plane oriented NNW-SSE, suggesting they occurred around a conduit related to the intrusion of magmatic-hydrothermal fluids into the craters. The frequency of VT earthquakes gradually increased from 6 September 2014 and reached a peak on 11 September 2014. After the peak, seismicity levels remained elevated until the eruption. b-values gradually increased from 1.2 to 1.7 from 11 to 16 September 2014 then declined gradually and dropped to 0.8 just before the eruption. During the 10-min period immediately preceding the phreatic eruption, VT earthquakes migrated in the up-dip direction as well as laterally along the NNW-SSE feature. The migrating seismicity coincided with an accelerated increase of pre-eruptive tremor amplitude and with an anomalous tiltmeter signal that indicated summit upheaval. Therefore, the migrating seismicity suggests that the vertical conduit was filled with pressurized fluids, which rapidly propagated to the surface during the final 10 min before the eruption.

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Section: Relocation Of Template Earthquakesmentioning

confidence: 99%

Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan

et al. 2015

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“…Previous passive‐ and active‐source velocity tomography studies of other volcanoes have found a variety of types of features in the subsurface. Compiling results from 23 active arc volcanoes (Aso [ Sudo and Kong , ], Augustine [ Syracuse et al ., ], Mount Etna [ Aloisi et al ., ; Laigle et al ., ], Mount Fuji [ Nakamichi et al ., ], Great Sitkin [ Pesicek et al ., ], Iwate [ Tanaka et al ., ], Katmai [ Murphy et al ., ], Kirishima [ Tomatsu et al ., ], Klyuchevskoy [ Koulakov et al ., ], Long Valley Caldera [ Seccia et al ., ], Montserrat [ Paulatto et al ., ], Mount St. Helens [ Lees , ; Waite and Moran , ], Naruko [ Nakajima and Hasegawa , ], Nevado del Ruiz [ Londoño and Sudo , ], Okmok [ Masterlark et al ., ; Ohlendorf et al ., ], Popocatépetl [ Berger et al ., ; Kuznetsov and Koulakov , ], Rainier [ Moran et al ., ], Redoubt [ DeShon et al ., ], Taranaki [ Sherburn et al ., ], Tongariro [ Rowlands et al ., ], Tungurahua [ Molina et al ., ], Unzen [ Ohmi and Lees , ], and Vesuvius [ Piana Agostinetti and Chiarabba , ]) show that upper crustal low‐velocity regions, potentially indicative of hotter or melt‐rich areas, are as common as high‐velocity regions, generally interpreted to be cooled basaltic rocks intruded during previous eruptions and near which magma travels to the surface. It is possible that all volcanoes contain both these features, but resolution limitations prevent their observation.…”

Section: Resultsmentioning

confidence: 99%

Seismicity and structure of Akutan and Makushin Volcanoes, Alaska, using joint body and surface wave tomography

et al. 2015

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Joint inversions of seismic data recover models that simultaneously fit multiple constraints while playing upon the strengths of each data type. Here we jointly invert 14 years of local earthquake body wave arrival times from the Alaska Volcano Observatory catalog and Rayleigh wave dispersion curves based upon ambient noise measurements for local V p , V s , and hypocentral locations at Akutan and Makushin Volcanoes using a new joint inversion algorithm. The velocity structure and relocated seismicity of both volcanoes are significantly more complex than many other volcanoes studied using similar techniques. Seismicity is distributed among several areas beneath or beyond the flanks of both volcanoes, illuminating a variety of volcanic and tectonic features. The velocity structures of the two volcanoes are exemplified by the presence of narrow high-V p features in the near surface, indicating likely current or remnant pathways of magma to the surface. A single broad low-V p region beneath each volcano is slightly offset from each summit and centered at approximately 7 km depth, indicating a potential magma chamber, where magma is stored over longer time periods. Differing recovery capabilities of the V p and V s data sets indicate that the results of these types of joint inversions must be interpreted carefully.

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“…The V P of the high‐velocity body beneath the summit obtained by the refraction survey is in the range of 4.5–5.0 km/s [ Oikawa et al , 2004], which is identical to that of the high‐velocity body found in our result. Shallow high‐velocity bodies have been found at other volcanoes by explosion seismic experiments [e.g., Tanaka et al , 2002; Yamawaki et al , 2004]. The high‐velocity body directly beneath the summit is considered to be the formation edifice and the manifestation of a near‐solid magma system beneath Mount Fuji.…”

Section: Discussionmentioning

confidence: 99%

“…This method uses the pseudobending (PB) ray‐tracing algorithm [ Um and Thurber , 1987] to determine rays and traveltimes between events and stations. The PB method has been frequently used for exploring volcanoes where large velocity perturbations are expected to exist [e.g., Chiarabba et al , 2000; Tanaka et al , 2002; Yamawaki et al , 2004]. …”

Section: Methods and Tomography Proceduresmentioning

confidence: 99%

Three‐dimensional velocity structures of Mount Fuji and the South Fossa Magna, central Japan

2007

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[1] We present the three-dimensional structures of the P wave velocity (V P ), S wave velocity (V S ) as well as the P wave to S wave velocity ratio (V P /V S ) beneath Mount Fuji and the South Fossa Magna, Japan, using arrival time data collected from 2002 to 2005 by a dense seismograph array. The high-resolution data set and improved methodology reveal not only several velocity features that are consistent with previous studies but also important new details that clarify the velocity structures associated with volcanic processes beneath Mount Fuji and the collision tectonics of the South Fossa Magna. One such particular feature is a low-V P , low-V S and low-V P /V S anomaly at depths of 7-17 km beneath Mount Fuji that corresponds with the locations of deep low-frequency (DLF) earthquakes. The coincidence of the velocity anomaly and the DLF locations suggests that supercritical volatile fluid, such as H 2 O and CO 2 , may be abundant in the low-V P /V S region and may play an important role in generating DLF earthquakes. This anomaly overlies a deeper low-V P , low-V S and high-V P /V S anomaly at depths of 15-25 km that may represent a zone of basaltic partial melt. A low-V P , low-V S and low-V P /V S anomaly is seen at depths of 6-14 km beneath Mount Hakone. Isovelocity surfaces (V P = 6.0 km/s and V S = 3.5 km/s) corresponding to the upper limit of hypocenter distribution below Mount Fuji may define the upper surface of the Philippine Sea plate whose existence in a seismic gap beneath Mount Fuji has been controversial.

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Three‐dimensional P‐wave velocity structure of Iwate volcano, Japan from active seismic survey

Cited by 41 publications

References 12 publications

Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan

Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan

Seismicity and structure of Akutan and Makushin Volcanoes, Alaska, using joint body and surface wave tomography

Three‐dimensional velocity structures of Mount Fuji and the South Fossa Magna, central Japan

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