First hand observations from the April 28, 2021 Sonitpur (MW 6.4) earthquake, Assam, India: possible mechanism involved in the occurrence of widespread ground effects

Joshi, Mrinal; Naik, Sambit Prasanajit; Mohanty, Asmita; Bhadran, Arun; Girishbai, Drishya; Ghosh, Swakangkha

doi:10.1007/s12303-022-0032-z

Cited by 5 publications

(7 citation statements)

References 62 publications

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“…The substantial damage in these regions further indicated the impact of the local soil characteristics. Thus, the localized ground effects observed align with findings reported by [38][39][40] in other earthquake studies (Pohang Earthquake, Sonitpur Earthquake). Sharma et al [23] have also discussed the similar effects of surface geology and topography on the damage severity during the 2015 Gorkha Nepal Earthquake.…”

Section: Seismically Induced Geotechnical Impactssupporting

confidence: 89%

Reconnaissance of the Effects of the MW5.7 (ML6.4) Jajarkot Nepal Earthquake of 3 November 2023, Post-Earthquake Responses, and Associated Lessons to Be Learned

Subedi,

KC,

Sharma

et al. 2024

Geosciences

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On 3 November 2023, a moment magnitude (MW) 5.7 (Local Magnitude, ML6.4) earthquake struck the western region of Nepal, one of the most powerful seismic events since 1505 in the region. Even though the earthquake was of moderate magnitude, it caused significant damage to several masonry buildings and caused slope failures in some regions. The field reconnaissance carried out on 6–9 November by the study team, following the earthquake, conducted the first-hand preliminary damage assessment in the three most affected districts—Jajarkot; West Rukum; and Salyan. This study covers the observed typical structural failures and geotechnical case studies from the field study. To have a robust background understanding, this paper examines the seismotectonic setting and regional seismic activity in the region. The observations of earthquake damage suggest that most of the affected buildings were made of stone or brick masonry without seismic consideration, while most of the reinforced concrete (RC) buildings remained intact. Case histories of damaged buildings, the patterns, and the failure mechanisms are discussed briefly in this paper. Significant damage to Khalanga Durbar, a historical monument in Jajarkot, was also observed. Medium- to large-scale landslides and rockfalls were recorded along the highway. The motorable bridge in the Bheri River suffered from broken bolts, rotational movement at the expansion joint, and damage to the stoppers. The damage observations suggest that, despite the existence of building codes, their non-implementation could have contributed to the heavy impact in the region. This study highlights that the local population faces a potential threat of subsequent disasters arising from earthquakes and earthquake-induced landslides. This underscores the necessity for proactive measures in preparedness for future disasters.

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Section: Seismically Induced Geotechnical Impactssupporting

confidence: 89%

Reconnaissance of the Effects of the MW5.7 (ML6.4) Jajarkot Nepal Earthquake of 3 November 2023, Post-Earthquake Responses, and Associated Lessons to Be Learned

Subedi,

KC,

Sharma

et al. 2024

Geosciences

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Section: Hydrochemical Anomaliessupporting

confidence: 78%

“…There is a possibility that the Brahmaputra River water maintained the flow toward the aquifer at OW1 for a shorter period (in our case 2-week anomaly period), which is in line with the transient water fluctuations observed in the epicentral area of the mainshock (E1) by Joshi et al (2023) and Bhadran et al (2022). Joshi et al (2023) documented a temporary reactivation of dry streams with a rapid rise in water levels, while rivers and ponds experienced a transient increase (∼0.5 m) in water levels. Bhadran et al (2022) reported that groundwater levels in dug wells abruptly rose by 4-6 m. They also observed a significant decline in water levels in the Gabharu River (a northern bank tributary of the Brahmaputra River at a distance of ∼106 km from OW1) by the fourth day, with complete drying before the fourteenth day following the mainshock.…”

Section: Hydrochemical Anomaliessupporting

confidence: 78%

“…They also observed that the region located to the north of the Brahmaputra River, where OW1 and OW2 are situated, is subsiding at a faster rate (−25 to −75 mm/yr) compared to the southern part (−0.1 to −15 mm/yr). Extensive ground effects, such as liquefaction, lateral spreading, ground cracks (ranging from 30 cm to 75 m in length), and structural damage, were observed as far as ∼100 km from the epicenter (Joshi et al., 2023 and Figure S4 in Supporting Information ).…”

Section: Discussionmentioning

confidence: 99%

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Water Geochemistry and Stable Isotope Changes Record Groundwater Mixing After a Regional Earthquake in Northeast India

Kumar,

Manga,

Nair

et al. 2024

Geochem Geophys Geosyst

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Recorded earthquake‐induced changes in hydrogeological systems date back over 2,000 years. As a part of our ongoing hydrogeochemical monitoring effort to study such changes, we collected 406 groundwater samples twice a week between February 2021 and July 2023 from two bore wells in the Kopili fault zone of Northeast India. We analyzed stable isotope ratios (δ2H, δ18O) and dissolved element concentrations to obtain a 2.5‐year hydrogeochemical time series and responses to multiple regional earthquakes (Mw ≥ 3) within the monitored period. We find significant but transient anomalies in both the chemical and isotopic composition of groundwater at one of the observation wells (OW1) after the 2021 Assam Mw 6.4 earthquake, followed by prolonged alterations in the hydrochemistry at both wells. We do not identify any precursory changes. Using multivariate statistical techniques and analyzing compositional changes before and after the mainshock, we infer that the hydrochemical anomalies at OW1, representing an immediate response to the mainshock, can be attributed to the potential breach of a hydrological barrier. This, in turn, allowed the infiltration of new water into the OW1 aquifer, potentially sourced from the nearby Brahmaputra River. Subsequently, during the post‐anomaly period, the earthquake‐induced fracturing and the associated changes in permeability sustained a prolonged period of mixing between surface water and groundwater, resulting in newly formed hydrochemistry at both wells. Our findings highlight the dynamic nature of aquifer properties during earthquakes. Long‐term continuous evaluation of such changes may provide new insights into feedback between tectonics and fluid flow in the crust.

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“…locking depth and slip rate of the fault when the accumulation time and fault length ar fixed. Therefore, the slip rate and locking depth are two important parameters for as sessing the seismic hazard and tectonic activity of an active fault [34]. Velocity profiles ca provide direct observations to determine the slip rate and locking depth.…”

Section: Inversion Of Slip Rate and Locking Depth Along The Weihe Faultmentioning

confidence: 99%

Characterizing Crustal Deformation of the Weihe Fault, Weihe Basin (Central China), Using InSAR and GNSS Observations

2023

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The Weihe Fault is an important basement fault that is buried deep and controls the formation, evolution, and seismicity of the Weihe Basin. It has been quiescent for more than 300 years with only a few moderate and small earthquakes distributed unevenly. Therefore, it is necessary to investigate the current tectonic deformation pattern in order to assess regional seismic risk. In this context, the tectonic deformation velocities of the Weihe Fault were analyzed using an interferometric synthetic aperture radar (InSAR), a global navigation satellite system (GNSS) and leveling observations. The line of slight (LOS) deformation rates spanning from 2015 to 2019 were estimated from stacking-InSAR technology. Subsequently, the three-dimensional deformation rates in the north–south, east–west, and vertical directions were separated through the integration of GNSS-derived horizontal deformation and InSAR-derived LOS deformation. After that, the long-wavelength tectonic deformation was decomposed from the separated vertical deformation based on the spherical wavelet multiscale approach. Finally, the slip rate and locking depth were inverted for the assessment of the seismic hazard and tectonic activity of the Weihe Fault. The results show that the separated vertical deformation is consistent with the leveling observations, where the standard deviation between them is 1.69 mm/yr and the mean value is 0.6 mm/yr, demonstrating the reliability of the proposed method. The decomposed long-wavelength tectonic deformation exhibits uplift in the north and subsidence in the south, as well as the obvious vertical velocity gradient. The inversion result shows that the slip rate of the Weihe Fault gradually decreases from the west to the east, and the dip gradually increases from the west to the east, indicating a segmented activity and the geometric characteristics of the fault. The locking depth of the Weihe Fault gradually increases from the west (~5 km) to the east (~14 km), implying a higher stress accumulation and seismic risk on the eastern section of the fault. Taking into account the higher locking depth and frequent historical earthquakes on the eastern section of the Weihe Fault, further attention should be paid to the earthquake risk of the eastern section of the Weihe Fault.

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First hand observations from the April 28, 2021 Sonitpur (MW 6.4) earthquake, Assam, India: possible mechanism involved in the occurrence of widespread ground effects

Cited by 5 publications

References 62 publications

Reconnaissance of the Effects of the MW5.7 (ML6.4) Jajarkot Nepal Earthquake of 3 November 2023, Post-Earthquake Responses, and Associated Lessons to Be Learned

Reconnaissance of the Effects of the MW5.7 (ML6.4) Jajarkot Nepal Earthquake of 3 November 2023, Post-Earthquake Responses, and Associated Lessons to Be Learned

Water Geochemistry and Stable Isotope Changes Record Groundwater Mixing After a Regional Earthquake in Northeast India

Characterizing Crustal Deformation of the Weihe Fault, Weihe Basin (Central China), Using InSAR and GNSS Observations

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