Tomography of the Source Area of the 1995 Kobe Earthquake: Evidence for Fluids at the Hypocenter?

Zhao, Dapeng; Kanamori, Hiroo; Negishi, Hideyo; Wiens, Douglas A.

doi:10.1126/science.274.5294.1891

Cited by 344 publications

(224 citation statements)

References 23 publications

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“…This is consistent with the suggestions of Benloft [1951] that the existence of aftershocks is related to a stress anomaly that dies away due to viscoelastic creep. The stress rotation might imply the existence of inelastic processes in the rupture zone, e.g., fluids [Johnson and McEvilly, 1995;Zhao et al, 1996]. The theory of Benloft [1951] only shows a change in stress magnitudes, not a rotation of the principal axes as observed during the Coalinga, Landers, and Northridge sequences.…”

Section: This Difference (2 •) Is Insignificant Since the Er-mentioning

confidence: 99%

State of stress before and after the 1994 Northridge Earthquake

Zhao¹,

Kanamori²,

Wiens³

1997

Geophysical Research Letters

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Abstract.The state of tectonic stress in the epicentral area of the 17 January 1994, Northridge earthquake (Mw 6.7) is investigated by applying a stress inversion method to P-wave polarity data from earthquakes in Northridge from July 1981 to January 1994 and from the Northridge aftershocks during January 1994 to December 1995. A 3-D crustal model is used to trace the rays taking off from the hypocenter, which reduced the effects of large structural heterogeneities on the determination of the stress tensor. We found significant temporal changes of stress orientations induced by the Northridge earthquake. The principal pressure (P) axis is oriented N32øE from 1981 to June 1992, and N30øE from 28 June 1992 to 16 January 1994, suggesting that the stress field in Northridge was not affected by the 1992 Landers earthquake. During two weeks following the Northridge mainshock, the P-axis is oriented N13øE, which is a significant (17 ø) change from that before the earthquake (N30øE). Between February 1994 and August 1995 the P-axis orientation changes from N18øE to N26øE, and finally ends up at N34øE by the end of 1995, which is close to that before the Northridge earthquake. These results suggest that the stresses to. rated coseismically, then rotated more slowly back to their original orientation. The aftershocks caused by the mainshock changed the stress distribution in the crust, which showed up as a regional stress change. The stress recovery appears to have completed within two years after the mainshock, which is very short compared to the time scale of the earthquake cycle.vided an excellent opportunity for investigating in more detail the possible temporal and spatial stress changes in the epicentral area before and after a major earthquake. The Northridge area is covered by the dense

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Section: This Difference (2 •) Is Insignificant Since the Er-mentioning

confidence: 99%

State of stress before and after the 1994 Northridge Earthquake

Zhao¹,

Kanamori²,

Wiens³

1997

Geophysical Research Letters

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“…One of the distinct features of the Kobe earthquake is that fluids were involved in the rupture nucleation as evidenced by numerous observations [see Zhao and Negishi, 1998 for a detailed review]. A highresolution tomographic study revealed that the Kobe mainshock hypocenter is located in a distinctive zone characterized by low P and $ wave velocities and a high Poisson's ratio [Zhao et al, 1996;Zhao and Negishi, 1998]. The anomalous zone exists in the depth range of 16 to 21 km and extends 15 to 20 km laterally, and is interpreted as a fluid-filled, fractured rock matrix that contributed to the initiation of the Kobe earthquake [Zhao and Negishi, 1998].…”

Section: Introductionmentioning

confidence: 99%

Crack density and saturation rate in the 1995 Kobe Earthquake Region

Zhao

Mizuno

1999

Geophysical Research Letters

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“…One plausible explanation is the existence of anhydrous plutonic rocks in this region (Yoshida, 2001), however, this interpretation needs further investigation. The presence of partial melt or fluids beneath the seismogenic zone in the lower crust structure can change the deformation of the fault zone and affect its stress accumulation (Zhao et al, 1996;Hasegawa et al, 2000Hasegawa et al, , 2005Nakajima et al, 2006).…”

Section: Interpretationsmentioning

confidence: 99%

“…For example, Zhao et al (1996) reported a low seismic velocity and a high Poisson's ratio anomaly around the hypocenter of the 1995 Kobe earthquake. They showed that this anomaly may be due to high pore fluid pressure and a fluid-filled, fractured rock matrix near the bottom of the seismogenic layer that contributed to the initiation of the Kobe earthquake.…”

Section: Introductionmentioning

confidence: 99%

High resolution seismic velocity structure around the Yamasaki fault zone of southwest Japan as revealed from travel-time tomography

et al. 2013

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The Yamasaki fault zone in southwestern Japan currently has a high potential for producing a large damaging earthquake. We carried out a seismic tomographic study to determine detailed crustal structures for the region. The velocity model clearly images a low-velocity and high V p /V s (high Poisson's ratio) anomaly in the lower crust beneath the Yamasaki fault zone at a depth of ∼15-20 km. This anomaly may be associated with the existence of partially-melted minerals. The existence of this anomaly below the fault zone may contribute to changing the long-term stress concentration in the seismogenic zone.

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Tomography of the Source Area of the 1995 Kobe Earthquake: Evidence for Fluids at the Hypocenter?

Cited by 344 publications

References 23 publications

State of stress before and after the 1994 Northridge Earthquake

State of stress before and after the 1994 Northridge Earthquake

Crack density and saturation rate in the 1995 Kobe Earthquake Region

High resolution seismic velocity structure around the Yamasaki fault zone of southwest Japan as revealed from travel-time tomography

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