Focal Mechanism Analyses of Aftershocks of the 1984 Western Nagano Prefecture Earthquake.

Yamazaki, Fumihito; Horiuchi, Shigeki; Itō, Kiyoshi; Moriya, Toshio; Nishigami, K.; Ooida, Tooru; Ouchi, Toru; Tanada, Toshikazu; Tsukuda, Tameshige; Aoki, Harumi; Fujii, Itsuhiro; Haneda, Toshio; Hasegawa, Akira; Hashimoto, Shinichi; Hirahara, Kazuro; Hirano, N.; Hirata, Naoshi; Iio, Yoshihisa; Ikami, Akira; Ishiketa, Yukio; Ito, Akihiko; Kanazawa, Toshihiko; Kaneshima, Satoshi; Karakama, Ikuo; Kobayashi, Mitsuo; Koizumi, Makoto; Kono, Toru; Kosuga, Masahiro; Kurata, Yuji; Kuriyama, Satoru; Kuroiso, Akio; Matsuzawa, Toru; Mikumo, Takeshi; Mitsunami, Toshio; Miura, Katsumi; Miura, Kazuaki; Miyajima, Rikio; Miyamachi, Hiroki; Mizoue, Megumi; Nakajima, Atsushi; Nakamura, Isao; Nakamura, Masaru; Nakayama, Tôru; Oike, Kazuo; Okamoto, T.; Okuda, Tetsuya; Saeki, Tatsuo; Sakai, Kimitoshi; Shibutani, Takuo; Suzuki, Masayuki; Suzuki, Sadaomi; Takahashi, Masayoshi; Takagi, Akio; Takeuchi, Fumiaki; Tomita, Sakura; Umeda, Yasuhiro; Wada, Hiroo; Yabuki, Tetsuichiro; Yamada, Mamoru; Yamamoto, Akihiko; Yamashina, Ken’ichiro; Yokohama, Manabu

doi:10.4294/jpe1952.40.327

Cited by 10 publications

(4 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thirty‐six temporary stations were installed just above the aftershock region of the Western Nagano Prefecture earthquake over a period of 52 days, starting 1 September 1986 [ Yamazaki et al , 1992] (Figures 1a–1c). We defined this observation period as term A in the following sections.…”

Section: Datamentioning

confidence: 99%

“…This activity has stayed very high in the form of swarm‐like earthquake activity even 20 years after the main shock. Many earthquake hypocenters and their focal mechanisms are well constrained by the dense seismic array in the aftershock region [ Yamazaki et al , 1992; Iio , 1995a]. These data sets are useful in estimating the detailed stress field after the main shock.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Detailed spatial changes in the stress field of the 1984 western Nagano earthquake region

Yukutake¹,

Iio²,

Horiuchi³

2010

J. Geophys. Res.

Self Cite

View full text Add to dashboard Cite

[1] We estimate the stress field after the 1984 western Nagano earthquake from numerous focal mechanisms. To precisely determine the focal mechanisms, we analyze the earthquakes that occurred around the eastern part of the main shock fault, where station coverage is fairly good. Most of the earthquakes that occurred in this part, except the main shock fault, are reverse fault types. In contrast, earthquakes that occurred near the main shock fault have T axes distributed in a belt (strike slip, oblique slip, and reverse fault types occurred equally). Using the stress inversion method to quantitatively estimate the stress field of these earthquakes revealed that the s 2 axis near the main shock fault is close to the vertical direction, whereas it is close to the horizontal direction in other regions. At the western edge of the study area, we observe that the s 1 axis rotates toward the NS direction and that the stress ratio (s 1 − s 2 )/(s 1 − s 3 ) is low. We estimate that the magnitude of s hmin decreases near the main shock fault. Spatial variation of the stress field around the eastern part of the main shock fault is not generated by static stress changes caused by the main shock. Local stress anomalies might have occurred around the main shock fault before the main shock.

show abstract

Section: Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Detailed spatial changes in the stress field of the 1984 western Nagano earthquake region

Yukutake¹,

Iio²,

Horiuchi³

2010

J. Geophys. Res.

Self Cite

View full text Add to dashboard Cite

show abstract

“…1), microseismic swarm activity suddenly began to occur in 1976 (Aoki et al 1980). The vigorous activity has continued for more than four decades since then, and the source region has become enlarged and migrated to the north and east flanks of the mountain (e.g., Ooida et al 1989;Yamazaki et al 1992;Rydelek et al 2002;Terakawa et al 2013b). During this period, this volcano produced four recorded eruptions (hydrothermal type) with volcanic explosivity index values of 0-2 in 19790-2 in , 19910-2 in , 20070-2 in , and 20140-2 in (e.g., Sawada 1981Nakamichi et al 2009;Yamaoka et al 2016).…”

Section: Introductionmentioning

confidence: 99%

“…During this period, this volcano produced four recorded eruptions (hydrothermal type) with volcanic explosivity index values of 0-2 in 19790-2 in , 19910-2 in , 20070-2 in , and 20140-2 in (e.g., Sawada 1981Nakamichi et al 2009;Yamaoka et al 2016). In 1984, 5 years after the first historic eruption, the western Nagano prefecture earthquake (M 6.8) occurred in the source region of the microseismic swarm (e.g., Ooida et al 1989;Horiuchi et al 1992;Yamazaki et al 1992). The diverse seismicity was suspected to be linked to volcanic eruptions through fluids in the porous network in the underground rock (e.g., Sano et al 1986), but the relationship among the fluids, diverse seismicity, and eruptions is enigmatic.…”

Section: Introductionmentioning

confidence: 99%

Overpressurized fluids drive microseismic swarm activity around Mt. Ontake volcano, Japan

Terakawa

2017

Earth Planets Space

View full text Add to dashboard Cite

Microseismic swarm activity has taken place since 1976 around Mt. Ontake, the second highest stratovolcano in Japan. This activity is thought to be linked to high pore-fluid pressure in the vicinity of the volcano. We analyzed well-constrained focal mechanism solutions of microseismicity to re-estimate the 3-D pore-fluid pressure field driving vigorous swarm activity around Mt. Ontake. Pore-fluid pressures were measured by mapping earthquake focal mechanisms on the 3-D Mohr diagram for the regional stress field with high resolutions of 2-5 km. The assumption of the reference stress pattern can cause modeling errors in measurements of pore-fluid pressure. To remove the effect, we statistically evaluated the estimation errors of the regional stress field and included these errors in the analysis. We detected an overpressurized fluid reservoir with a peak of about 10-30 MPa in the east flank of Mt. Ontake, where microseismic swarm activity has been vigorous for the last two decades. The level of pore-fluid pressure was maintained for at least 5 years after 2009. This finding indicates that there are some interactions between the intensive swarm activity and overpressurized fluids: the swarm activity has been driven by overpressurized fluids, whereas porefluid pressures have been suppressed by the swarm activity.

show abstract

Effects of pore fluid pressure and tectonic stress on diverse seismic activities around the Mt. Ontake volcano, central Japan

et al. 2013

View full text Add to dashboard Cite

Focal Mechanism Analyses of Aftershocks of the 1984 Western Nagano Prefecture Earthquake.

Cited by 10 publications

References 4 publications

Detailed spatial changes in the stress field of the 1984 western Nagano earthquake region

Detailed spatial changes in the stress field of the 1984 western Nagano earthquake region

Overpressurized fluids drive microseismic swarm activity around Mt. Ontake volcano, Japan

Effects of pore fluid pressure and tectonic stress on diverse seismic activities around the Mt. Ontake volcano, central Japan

Contact Info

Product

Resources

About