Focal depths and mechanisms of shallow earthquakes in the Himalayan–Tibetan region

Bai, Ling; Li, Guohui; Khan, Nasrullah; Zhao, Junmeng; Ding, Lin

doi:10.1016/j.gr.2015.07.009

Cited by 51 publications

(34 citation statements)

References 61 publications

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“…Understanding the deformation mechanisms dominant in frictional shearing of fault gouge is important for physically based modeling and prediction of seismic/aseismic fault slips in the crust. As two major constituents in the lower crust, plagioclase and pyroxene have been found to be velocity weakening in frictional shearing at temperatures in the lower crust under hydrothermal conditions [ He et al ., ], which property may provide a clue for questions as to why some earthquakes beneath Shillong plateau, India [ Maggi et al ., ; Bai et al ., ] and tremors on the San Andreas fault [ Shelly and Hardebeck , ] occur in the lower crust. However, recognizing the dominant deformation mechanism related to frictional shearing is not a simple task.…”

Section: Introductionmentioning

confidence: 99%

Comparing dry and wet friction of plagioclase: Implication to the mechanism of frictional evolution effect at hydrothermal conditions

Tan

Zhang

2016

JGR Solid Earth

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To understand mechanism for unstable velocity‐weakening slip behavior of plagioclase at hydrothermal conditions in the lower crust, we employed nominally dry experiments on plagioclase gouge to isolate fluid‐assisted processes that may be activated at hydrothermal conditions and obtained constitutive parameters fitted to rate and state friction laws with temperatures of 99–617°C and confining pressure of 150 MPa, allowing comparison to the hydrothermal counterpart. While the direct effect (a value) has relatively high values of 0.007–0.01 in the high temperature range above 300–400°C, the evolution effect (b value) shows a diminishing trend from peak values of 0.0075 and 0.0057, respectively, at 305°C and 400°C down to ~0 at 617°C, in contrast to the increasing trend in both effects at hydrothermal conditions. The evolution effect in the dry experiments may be controlled by structural changes related to degrees of shear localization and evolution of porosity change rate in response to a change in loading rate. The evolution effect in dry friction compared to the thermally enhanced, much stronger one at hydrothermal conditions suggests activation of fluid‐assisted time‐dependent mechanism operating in the wet experiments.

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Section: Introductionmentioning

confidence: 99%

Comparing dry and wet friction of plagioclase: Implication to the mechanism of frictional evolution effect at hydrothermal conditions

Tan

Zhang

2016

JGR Solid Earth

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“…Active faults exist throughout the Kathmandu basin [Nakata et al, 1990]. However, strike-slip earthquakes on these near-vertical faults have not been recorded in the past 50 years [Bai et al, 2016]. Great earthquakes in the past 200 years include the 26 August 1833 M w 8.0 event [Bilham, 1995] and the 15 January 1934 M w 8.0 Bihar-Nepal event [Sapkota et al, 2012] (Figure 1), which have been attributed to slip on the MHT.…”

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confidence: 99%

Faulting structure above the Main Himalayan Thrust as shown by relocated aftershocks of the 2015 M_w7.8 Gorkha, Nepal, earthquake

Bai

Liu

Ritsema

et al. 2016

Geophysical Research Letters

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The 25 April 2015, Mw7.8 Gorkha, Nepal, earthquake ruptured a shallow section of the Indian‐Eurasian plate boundary by reverse faulting with NNE‐SSW compression, consistent with the direction of current Indian‐Eurasian continental collision. The Gorkha main shock and aftershocks were recorded by permanent global and regional arrays and by a temporary local broadband array near the China‐Nepal border deployed prior to the Gorkha main shock. We relocate 272 earthquakes with Mw>3.5 by applying a multiscale double‐difference earthquake relocation technique to arrival times of direct and depth phases recorded globally and locally. We determine a well‐constrained depth of 18.5 km for the main shock hypocenter which places it on the Main Himalayan Thrust (MHT). Many of the aftershocks at shallower depths illuminate faulting structure in the hanging wall with dip angles that are steeper than the MHT. This system of thrust faults of the Lesser Himalaya may accommodate most of the elastic strain of the Himalayan orogeny.

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“…For example, Nath and Thingbaijam () identified that this study region belongs to the active shallow crustal regime (ACR) with many subduction zone interface (SZI) earthquakes across the Himalaya. Earthquake focal depth and mechanism study (Bai et al, ) stated that the occurrence of large earthquakes is fairly associated with subduction interface in this region. Moreover, it was assumed by some previous seismic hazard studies that the Himalaya and its surrounding region belongs to either SIZ or ACR (e.g., Ram and Wang GX, ), or both (e.g., Chaulagain et al, ).…”

Section: Methodsmentioning

confidence: 94%

Probabilistic seismic hazard assessment of Nepal using multiple seismic source models

Rahman

Bai

2018

Earth and Planetary Physics

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The potential for devastating earthquakes in the Himalayan orogeny has long been recognized. The 2015 MW7.8 Gorkha, Nepal earthquake has heightened the likelihood that major earthquakes will occur along this orogenic belt in the future. Reliable seismic hazard assessment is a critical element in development of policy for seismic hazard mitigation and risk reduction. In this study, we conduct probabilistic seismic hazard assessment using three different seismogenic source models (smoothed gridded, linear, and areal sources) based on the complicated tectonics of the study area. Two sets of ground motion prediction equations are combined in a standard logic tree by taking into account the epistemic uncertainties in hazard estimation. Long‐term slip rates and paleoseismic records are also incorporated in the linear source model. Peak ground acceleration and spectral acceleration at 0.2 s and 1.0 s for 2% and 10% probabilities of exceedance in 50 years are estimated. The resulting maps show significant spatial variation in seismic hazard levels. The region of the Lesser Himalaya is found to have high seismic hazard potential. Along the Main Himalayan Thrust from east to west beneath the Main Central Thrust, large earthquakes have occurred regularly in history; hazard values in this region are found to be higher than those shown on existing hazard maps. In essence, the combination of long span earthquake catalogs and multiple seismogenic source models gives improved seismic hazard constraints in Nepal.

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Focal depths and mechanisms of shallow earthquakes in the Himalayan–Tibetan region

Cited by 51 publications

References 61 publications

Comparing dry and wet friction of plagioclase: Implication to the mechanism of frictional evolution effect at hydrothermal conditions

Comparing dry and wet friction of plagioclase: Implication to the mechanism of frictional evolution effect at hydrothermal conditions

Faulting structure above the Main Himalayan Thrust as shown by relocated aftershocks of the 2015 M_w7.8 Gorkha, Nepal, earthquake

Probabilistic seismic hazard assessment of Nepal using multiple seismic source models

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Focal depths and mechanisms of shallow earthquakes in the Himalayan–Tibetan region

Cited by 51 publications

References 61 publications

Comparing dry and wet friction of plagioclase: Implication to the mechanism of frictional evolution effect at hydrothermal conditions

Comparing dry and wet friction of plagioclase: Implication to the mechanism of frictional evolution effect at hydrothermal conditions

Faulting structure above the Main Himalayan Thrust as shown by relocated aftershocks of the 2015 Mw7.8 Gorkha, Nepal, earthquake

Probabilistic seismic hazard assessment of Nepal using multiple seismic source models

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Faulting structure above the Main Himalayan Thrust as shown by relocated aftershocks of the 2015 M_w7.8 Gorkha, Nepal, earthquake