The 2001 Bhuj earthquake: Tomographic evidence for fluids at the hypocenter and its implications for rupture nucleation

Kayal, J. R.; Zhao, Dapeng; Mishra, O. P.; De, Reena; Singh, O. P.

doi:10.1029/2002gl015177

Cited by 139 publications

(95 citation statements)

References 14 publications

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“…Scale bars: 20 µm. the hypocenter of the disastrous 1995 Kobe earthquake (Mw 7.2) in Japan (Zhao et al, 1996Salah and Zhao, 2003), the catastrophic 2001 Bhuj earthquake (Mw 7.6) in India (Kayal et al, 2002), and at least some earthquakes along the San Andreas fault in California (Unsworth et al, 1997;Bedroisan et al, 2002). These earthquakes are characterized by low seismic S-wave velocity and high Poisson's ratio and/or low resistivity, indicating that the anomaly may be due to fluid-filled rocks.…”

Section: Discussion and Geophysical Implicationsmentioning

confidence: 99%

Experimental Faulting of Serpentinite during Dehydration: Implications for Earthquakes, Seismic Low-Velocity Zones, and Anomalous Hypocenter Distributions in Subduction Zones

Jung

Green

2004

International Geology Review

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Dehydration embrittlement of serpentine was investigated by employing triaxial deformation experiments at high pressure and temperature (P = 1-6 GPa; T = 550-820ºC). A modified Griggs apparatus was used up to 3.4 GPa and a Walker-type multi-anvil apparatus was used at 3.5-6 GPa). The investigated specimen is a serpentinized peridotite from Val Malenco, Italy. Dehydration of the sample under differential stress resulted in faults associated with ultrafine-grained solid reaction products, formed as byproducts of antigorite dehydration. This phenomenon was observed under all conditions tested (1-6 GPa, 630-820ºC), independent of pressure, even though the sign of total volume change (∆V) of the dehydration reaction changes from positive to negative at 2.2 GPa. This observation confirms that dehydration embrittlement is a viable mechanism for triggering earthquakes independent of depth, so long as there is a hydrous mineral breaking down under differential stress. Aligned Mode-I cracks and fluid inclusion trails are common in relict olivines in the deformed serpentinite. We suggest that some of the puzzling observations, including a seismic lowvelocity zone (LVZ) at the top of subducting slabs, can be attributable to aligned fluid-filled Mode-I cracks and enhanced defect mobility in olivine in the presence of water. The anomalous hypocenter distributions of earthquakes can be attributed to the degree of dehydration of hydrous minerals in combination with a certain level of stress. In addition, low-seismicity regions in subduction zones may be explained by "superplastic" flow under low stress along the ultrafine-grained solid reaction products that are produced during dehydration reactions.

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Section: Discussion and Geophysical Implicationsmentioning

confidence: 99%

Experimental Faulting of Serpentinite during Dehydration: Implications for Earthquakes, Seismic Low-Velocity Zones, and Anomalous Hypocenter Distributions in Subduction Zones

Jung

Green

2004

International Geology Review

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“…This suggests one common feature: the significant influence of fluids and magma on the rupture nucleation of large crustal earthquakes. Significant structural heterogeneities, and their effects on the seismogenesis, are also revealed in the source areas of many large earthquakes in the continental regions (e.g., Lees, 1990;Michael and Eberhart-Phillips, 1991;Zhao and Kanamori, 1992, 1993Kayal et al, 2002;Zhao, 2004, 2009;Zhao et al, 2005;Mukhopadhyay et al, 2006;Qi et al, 2006;Tian et al, 2007a, b;Tian and Zhao, 2011). The occurrence of deep moonquakes seems also to be affected by structural heterogeneities in the lunar mantle, in addition to tidal forces Sakamaki et al, 2010;Zhao and Arai, 2011).…”

Section: Anatomy Of Large Crustal Earthquakesmentioning

confidence: 99%

Tomography and Dynamics of Western-Pacific Subduction Zones

Zhao¹

2012

Monogr. Environ. Earth Planets

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We review the significant recent results of multiscale seismic tomography of the Western-Pacific subduction zones and discuss their implications for seismotectonics, magmatism, and subduction dynamics, with an emphasis on the Japan Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V ) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V /low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the subducting slab. Seismic anisotropy seems to exist in all portions of the Northeast Japan subduction zone, including the upper and lower crust, the mantle wedge and the subducting Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep subduction of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest Japan. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, subducting slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under the Japan Sea and the East Asia margin may be related to a metastable olivine wedge in the subducting Pacific slab. The Pacific slab becomes stagnant in the mantle transition zone under East Asia, and a big mantle wedge (BMW) has formed above the stagnant slab. Convective circulations and fluid and magmatic processes in the BMW may have caused intraplate volcanism (e.g., Changbai and Wudalianchi), reactivation of the North China craton, large earthquakes, and other active tectonics in East Asia. Deep subduction and dehydration of continental plates (such as the Eurasian plate, Indian plate and Burma microplate) are also found, which have caused intraplate magmatism (e.g., Tengchong) and geothermal anomalies above the subducted continental plates. Under Kamchatka, the subducting Pacific slab shortens toward the north and terminates near the Aleutian-Kamchatka junction. The slab loss was induced by friction with the surrounding asthenosphere, as the Pacific plate rotated clockwise 30 Ma ago, and then it was enlarged by the slab-edge pinch-off b...

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“…Such changes are due to increase in crustal heterogeneities (Aki 1965;Wiemer and Wyss 1997;Wyss et al 2004), fluid-filled fractured rock mass. The strong heterogeneities within a mafic pluton are responsible for the accumulation of large crustal shear stress that results a lower crustal intraplate earthquake in this region (Kayal et al 2002;Mishra and Zhao 2003;Mandal et al 2004;Mandal and Pujol 2006;Mandal and Chadha 2008).…”

Section: Estimates Of 3d B-values Mapping In the 2001mentioning

confidence: 99%

Spatial variation of the aftershock activity across the Kachchh Rift Basin and its seismotectonic implications

Singh

Mishra²,

Kumar

et al. 2012

J Earth Syst Sci

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We analyzed 3365 relocated aftershocks with magnitude of completeness (Mc) ≥1.7 that occurred in the Kachchh Rift Basin (KRB) between August 2006 and December 2010. The analysis of the new aftershock catalogue has led to improved understanding of the subsurface structure and of the aftershock behaviour. We characterized aftershock behaviour in terms of a-value, b-value, spatial fractal dimension (D s ), and slip ratio (ratio of the slip that occurred on the primary fault and that of the total slip). The estimated b-value is 1.05, which indicates that the earthquake occurred due to active tectonics in the region. The three dimensional b-value mapping shows that a high b-value region is sandwiched around the 2001 Bhuj mainshock hypocenter at depths of 20-25 km between two low b-value zones above and below this depth range. The D s -value was estimated from the double-logarithmic plot of the correlation integral and distance between hypocenters, and is found to be 2.64 ± 0.01, which indicates random spatial distribution beneath the source zone in a two-dimensional plane associated with fluid-filled fractures. A slip ratio of about 0.23 reveals that more slip occurred on secondary fault systems in and around the 2001 Bhuj earhquake (Mw 7.6) source zone in KRB.

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The 2001 Bhuj earthquake: Tomographic evidence for fluids at the hypocenter and its implications for rupture nucleation

Cited by 139 publications

References 14 publications

Experimental Faulting of Serpentinite during Dehydration: Implications for Earthquakes, Seismic Low-Velocity Zones, and Anomalous Hypocenter Distributions in Subduction Zones

Experimental Faulting of Serpentinite during Dehydration: Implications for Earthquakes, Seismic Low-Velocity Zones, and Anomalous Hypocenter Distributions in Subduction Zones

Tomography and Dynamics of Western-Pacific Subduction Zones

Spatial variation of the aftershock activity across the Kachchh Rift Basin and its seismotectonic implications

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