Estimation of the stress field in the region of the 2000 Western Tottori Earthquake: Using numerous aftershock focal mechanisms

Yukutake, Yohei; Iio, Yoshihisa; Katao, Hiroshi; Shibutani, Takuo

doi:10.1029/2005jb004250

Cited by 27 publications

(35 citation statements)

References 26 publications

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“…3). These features of the focal mechanisms are consistent with those reported in previous studies (e.g., Yukutake et al 2007). We also evaluated the variety of the focal mechanisms based on the Kagan angle (1991) from the reference focal mechanism.…”

Section: Resultssupporting

confidence: 82%

“…The strike and dip angles of the reference focal mechanism were assumed to be those of the bestfit plane (Table 1). The rake angle of the reference focal mechanism was assumed to be parallel to the resolved shear stress direction on the best-fit plane under the stress field reported by Yukutake et al (2007), in which the stress field around the mainshock fault was estimated using a stress inversion method and focal mechanism data of the aftershocks.…”

Section: Estimation Of Subsurface Fault Structurementioning

confidence: 99%

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Why do aftershocks occur? Relationship between mainshock rupture and aftershock sequence based on highly resolved hypocenter and focal mechanism distributions

Yukutake

Iio

2017

Earth Planets Space

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In order to clarify the origin of aftershocks, we precisely analyze the hypocenters and focal mechanisms of the aftershocks following the 2000 Western Tottori Earthquake, which occurred in the western part of Japan, using data from dense seismic observations. We investigate whether aftershocks occur on the mainshock fault plane on which coseismic slip occurred or they represent the rupture of fractures surrounding the mainshock fault plane. Based on the hypocenter distribution of the aftershocks, the subsurface fault structure of the mainshock is estimated using principal component analysis. As a result, we can obtain the detail fault structure composed of 8 best-fit planes. We demonstrate that the aftershocks around the mainshock fault are distributed within zones of 1.0-1.5 km in thicknesses, and their focal mechanisms are significantly diverse. This result suggests that most of the aftershocks represent the rupture of fractures surrounding the mainshock fault rather than the rerupture of the mainshock fault. The aftershocks have a much wider zone compared with the exhumed fault zone in field observations, suggesting that many aftershocks occur outside the fault damage zone. We find that most aftershocks except in and around the large-slip region are well explained by coseismic stress changes. These results suggest that the thickness of the aftershock distribution may be controlled by the stress changes caused by the heterogeneous slip distribution during the mainshock. The aftershock is also distributed within a much wider zone than the hypocenter distribution observed in swarm activity in the geothermal region, which is thought to be caused by the migration of hydrothermal fluid. This result implies a difference in generation processes: Stress changes due to the mainshock contribute primarily to the occurrence of aftershocks, whereas earthquake swarms in the geothermal region are caused by fluid migration within the localized zone.

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Section: Resultssupporting

confidence: 82%

Section: Estimation Of Subsurface Fault Structurementioning

confidence: 99%

Why do aftershocks occur? Relationship between mainshock rupture and aftershock sequence based on highly resolved hypocenter and focal mechanism distributions

Yukutake

Iio

2017

Earth Planets Space

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“…They installed three-component short-period velocity seismometers at most stations and recorded continuously with a sampling rate of 100 Hz. With this dense network data, a detailed distribution and focal mechanisms of the aftershocks, the three-dimensional velocity structure around the source region, and a regional stress field have been reported (Shibutani et al, 2005;Yukutake et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Spatial distribution of similar aftershocks of a large inland earthquake, the 2000 Western Tottori earthquake, in Japan

Hayashi

Hiramatsu

2013

Earth Planet Sp

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We detected similar aftershocks of the 2000 Western Tottori earthquake and we have examined their spatial distribution on the source fault. Many similar aftershocks are distributed in the northern part of the source fault, but few in the southern part. Specifically, similar aftershocks on the source fault are located outside of the asperity. The cumulative slip estimated from the similar aftershocks is 0.4-2.4 cm. The largest one is found at the edge of the major asperity. We observe that shallower events show a larger cumulative slip than deeper events. Large cumulative slip in the shallow depth in the northern part is coincident with the geodetic observation of afterslip. These facts suggest that similar aftershocks can provide information related to afterslip. However, the slip velocity estimated from both the slip and the recurrence interval of the similar aftershocks shows no distinct distribution.

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“…In this case, a coseismic rotation of the principal stress axis was clearly observed. However, no coseismic rotation of the principal stress axis was observed as a result of the 2000 western Tottori (M w 6.6) earthquake (Yukutake et al 2007). In this case, it is likely that only a small amount of the deviatoric stress was released by the mainshock.…”

Section: Discussionmentioning

confidence: 89%

Focal mechanisms and stress field in the Nobi fault area, central Japan

et al. 2015

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In this study, we obtained 728 focal mechanisms of small earthquakes with depths shallower than 20 km that occurred from May 2009 to May 2013 in the Nobi fault area in central Japan. The averages of the azimuths of the P-and T-axes were N97°± 23°E and N6°± 32°E, and the averages of the dips of the P-and T-axes were 11°± 10°a nd 32°± 25°, respectively. These variations in the P-and T-axes come from variation of the focal mechanisms; both strike-slip and reverse fault earthquakes were observed in the study area. A stress tensor inversion method was applied to the focal mechanisms, and we obtained and characterized the spatial pattern of the tectonic stress. We found that the maximum principal stress (σ 1 ) is oriented E-W over almost the entire study area. The stress ratio R, which is defined as R = (σ 1 -σ 2 )/(σ 1 -σ 3 ), ranges from 0.65 to 0.98, and the average R over the entire study area is 0.82. The average stress ratio is close to unity, indicating σ 2 ≈ σ 3 , and thus the dominant stress in this region is a uniaxial compression in the direction of σ 1 . The direction of the σ 1 -axis fluctuates locally at the southeastern end of the seismic fault ruptured by the 1891 Nobi earthquake. This fluctuation is limited to within a very narrow zone across the seismic fault in the upper crust shallower than approximately 10 km, suggesting that most of the deviatoric stress at the southeastern end of the seismic fault ruptured by the 1891 Nobi earthquake was not released.

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Estimation of the stress field in the region of the 2000 Western Tottori Earthquake: Using numerous aftershock focal mechanisms

Cited by 27 publications

References 26 publications

Why do aftershocks occur? Relationship between mainshock rupture and aftershock sequence based on highly resolved hypocenter and focal mechanism distributions

Why do aftershocks occur? Relationship between mainshock rupture and aftershock sequence based on highly resolved hypocenter and focal mechanism distributions

Spatial distribution of similar aftershocks of a large inland earthquake, the 2000 Western Tottori earthquake, in Japan

Focal mechanisms and stress field in the Nobi fault area, central Japan

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