Volatile element isotope systematics at Ontake volcano, Japan.

Takahata, Naoto; Yokochi, Reika; Nishio, Yoshiro; Sano, Yuji

doi:10.2343/geochemj.37.299

Cited by 16 publications

(15 citation statements)

References 27 publications

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“…Kasaya & Oshiman (2004) and Yoshimura et al (2011) modelled a low-resistivity region near the main shock hypocentre and swarm region. Takahata et al (2003) detected an anomalous temporal increase during 1996-2000 in δ 13 C values of CO 2 from a hydrothermal feature located directly above the swarm, as indicated by the blue inverted triangle in Fig. 1.…”

Section: G E O P H Y S I C a L S E T T I N G O F T H E 1 9 8 4 W E S mentioning

confidence: 99%

“…A dashed ellipse shows the uplift region estimated by Kimata et al (2004). The blue inverted triangle shows a hydrothermal feature with elevated δ 13 C values for CO 2 (Takahata et al 2003). damage and induced landslides. The earthquake's fault was interpreted by Yoshida & Koketsu (1990) as a right lateral, ENE-WSW trending one.…”

Section: G E O P H Y S I C a L S E T T I N G O F T H E 1 9 8 4 W E S mentioning

confidence: 99%

“…The bold line in (a) denotes the fault plane posited by Yoshida & Koketsu (1990). The dashed half ellipse and a blue inverted triangle in (c) show the uplift region (Kimata et al 2004) and the hydrothermal feature with elevated δ 13 C values for CO 2 (Takahata et al 2003), respectively. greater than 3 per cent reflects differences in crack density and/or fluid saturation of rocks.…”

Section: Velocities For the Bedrock Matrix In The Study Region And Thmentioning

confidence: 99%

“…Hypocentres are indicated by solid circles A red star and black rectangles denote the main shock epicentre and the fault plane (respectively) of the 1984 western Nagano Prefecture earthquake as estimated by Yoshida & Koketsu (1990). The dashed ellipse shows the ascending region estimated by Kimata et al (2004) and the blue inverted triangle marks a hydrothermal feature with elevated δ 13 C values for CO 2 (Takahata et al 2003). An example of a waveform and spectra observed from the network used in this study .…”

Section: E N S E a R R Ay Datamentioning

confidence: 99%

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Relationship between hypocentral distributions and Vp/Vs ratio structures inferred from dense seismic array data: a case study of the 1984 western Nagano Prefecture earthquake, central Japan

Doi

Noda

Iio

et al. 2013

Geophysical Journal International

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S U M M A R YWe conducted a three-dimensional traveltime tomographic reconstruction in and around the source region of the 1984 western Nagano Prefecture earthquake to investigate the generation process for the main shock and associated swarm activity. Up to 220 000 high-resolution traveltime records (2 ms error) were compiled from a dense seismic network. From these records, we performed accurate, high-resolution calculations to estimate hypocentre distributions and three-dimensional velocity structure. Most hypocentres aligned along the same path or within the same plane, rather than in three-dimensional clusters. Hypocentres in the swarm region are located in regions with low Vp/Vs ratios, while few earthquakes occurred in regions with high or normal Vp/Vs ratios. We suggest that differences in the number of small fractures and fluid content between these two regions influenced the seismic activity. Rupture propagation associated with the main shock appears to be confined by relatively higher Vp/Vs surroundings, and a low-velocity region which limits its vertical extent.Key words: Seismic tomography; Fractures and faults; Crustal structure. I N T RO D U C T I O NElucidating generation processes of earthquakes is critical for longterm forecasting and preparedness. At present, however, we do not fully understand how earthquakes-especially crustal earthquakes, are generated. Recently, studies have posited that the generation mechanism of crustal earthquakes relates to fluids in the crust. Iio et al. (2002) suggested that water issuing upwards from subducting slabs drives crustal earthquakes. Vidale & Shearer (2006) and Yukutake et al. (2011) also found that fluid diffusion may cause swarm migration.In studies of heterogeneous structures within the source regions of large earthquakes, low-velocity regions have been found adjacent to the hypocentre. Studies of waves trapped within fault zones found that fractures serve to lower wave velocity in the vicinity of the fault zone (Li et al. 1994;Mizuno et al. 2004). Using extremely highdensity aftershock observations, Okada et al. (2006) determined that parts of the 2004 Chuetsu earthquake faults were located in low-velocity regions. Hasegawa et al. (2009) reported that lowvelocity regions have been detected just beneath the main shock faults of many crustal earthquakes. Moreover, Tian et al. (2007) suggest that the existence of fluids weakens the rocks around the faults of crustal earthquakes to trigger large events in California. These studies suggest that fluids beneath the main shock hypocentre migrate into the fault zone and increase the pore pressure to generate the main shock. How fluids interact with subsurface structures, and how these interactions relate to earthquake generation, however, are not fully understood.In order to investigate the earthquake generation processes, Iio et al. (1999) installed a high-density seismic network in and around the source region of the 1984 Nagano Prefecture earthquake. Data from this network enable us to more precisely estim...

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Section: G E O P H Y S I C a L S E T T I N G O F T H E 1 9 8 4 W E S mentioning

confidence: 99%

Section: G E O P H Y S I C a L S E T T I N G O F T H E 1 9 8 4 W E S mentioning

confidence: 99%

Section: Velocities For the Bedrock Matrix In The Study Region And Thmentioning

confidence: 99%

Section: E N S E a R R Ay Datamentioning

confidence: 99%

See 2 more Smart Citations

Relationship between hypocentral distributions and Vp/Vs ratio structures inferred from dense seismic array data: a case study of the 1984 western Nagano Prefecture earthquake, central Japan

Doi

Noda

Iio

et al. 2013

Geophysical Journal International

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“…We have developed a similar system by using a modified noble gas mass spectrometer . This method has been successfully applied to mid-ocean ridge basalt glasses (Sano et al, , 2001Nishio et al, 1999), mineral spring gases (Takahata et al, 2003), olivine phenocrysts (Fischer et al, 2005), and Archean samples (Nishizawa et al, 2005(Nishizawa et al, , 2007. In this present work, we have used the same analytical system to measure nitrogen isotope ratios of a coral skeleton, to temporal resolution of one month.…”

Section: Introductionmentioning

confidence: 99%

High sensitivity measurements of nitrogen isotopic ratios in coral skeletons from Palau, western Pacific: Temporal resolution and seasonal variation of nitrogen sources

et al. 2008

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By using a step-wise heating method in conjunction with static vacuum mass spectrometry, we have measured at high temporal resolution (one month) the nitrogen isotopic ratio of a coral skeletal sample collected from Palau in the northern part of the Western Pacific. The δ 15 N value from the 900°C combustion step varies significantly, from +1.1‰ to +10.9‰ for the estimated time period from July 1995 to January 1998. The higher values occurred during winter and the lower values in summer. The δ 18 O and δ 13 C values of the skeleton were also analyzed for the same period, using conventional methods. The ranges of δ 18 O and δ 13 C variations are from -6.1‰ to -5.4‰ and from -1.6‰ to -0.9‰, respectively, which are significantly smaller than the δ 15 N variation. The δ 13 C change is possibly attributable to kinetic isotope effects, as deduced from a negative correlation between the δ 13 C value and mean sea surface temperature (SST) in the region. On the other hand, the δ 15 N variation could be derived from seasonal change of the relative ratio of two components utilized by symbiotic algae: a 15 N-depleted component from N 2 fixation and 15 N-enriched nitrate from the tropical oligotrophic open ocean.

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A magma‐hydrothermal system beneath Hakone volcano, central Japan, revealed by highly resolved velocity structures

et al. 2015

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High-resolution images of subsurface structures are necessary to understand the transport processes of crustal fluids from deep magma sources and their relationship to earthquake swarms in active volcanic regions. Based on a seismic tomography approach, we have developed a new model for the magma-hydrothermal system beneath Hakone volcano, central Japan, where shallow earthquake swarms and crustal deformation associated with inflation of an open-crack source are often observed. By applying travel-time data for local earthquakes to a tomographic inversion, we obtained highly resolved seismic velocity structures that show a region of low P-wave velocity (Vp), low S-wave velocity (Vs), and high Vp/Vs ratios at depths of 10-20 km beneath the volcano, corresponding to the location of the open-crack source. We suggest that the high Vp/Vs ratios represent a deep magma chamber with a high concentration of melt and/or fluids. Deep low-frequency earthquakes, located just beneath this high Vp/Vs zone, may indicate that magmatic fluids are supplied from below. Above the high Vp/Vs zone, a region of low Vp, low Vs, and low Vp/Vs ratios exists at depths of 3-10 km, suggesting the presence of crack-filled water or CO 2 supplied from the inferred deep magma chamber. Many earthquake swarms occur in this low Vp/Vs zone, indicating that crustal fluids play an important role in generating the swarms. Similar relationships between magma reservoirs, overlying hydrothermal systems, and swarm activity have been reported from other volcanic areas and thus may be a ubiquitous feature beneath active volcanoes.

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Volatile element isotope systematics at Ontake volcano, Japan.

Cited by 16 publications

References 27 publications

Relationship between hypocentral distributions and Vp/Vs ratio structures inferred from dense seismic array data: a case study of the 1984 western Nagano Prefecture earthquake, central Japan

Relationship between hypocentral distributions and Vp/Vs ratio structures inferred from dense seismic array data: a case study of the 1984 western Nagano Prefecture earthquake, central Japan

High sensitivity measurements of nitrogen isotopic ratios in coral skeletons from Palau, western Pacific: Temporal resolution and seasonal variation of nitrogen sources

A magma‐hydrothermal system beneath Hakone volcano, central Japan, revealed by highly resolved velocity structures

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