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The present seismicity catalog of Kumaun–Garhwal Himalaya, which includes the local earthquake events between 1991 and 2018 with magnitude (ML: 1–6.5), has been investigated for understanding the spatial-depth pattern of seismicity coupled with the geotectonic setting of the region. Additionally, the spatiotemporal behavior of microseismicity has also been assessed by investigating the frequency-magnitude distribution (b value) and fractal dimension (Dc). The b value was calculated by using the entire magnitude range (EMR) method, while the Dc value was calculated by adopting the correlation integral method. The microseismicity in the region is mainly concentrated across the hinterland region, especially along the Main Central Thrust (MCT) zone, where most of the earthquakes are confined to shallow depths coincident with the depth of the Main Himalayan Thrust (MHT). The maximum likelihood estimates for the whole region provide the b value as 0.75 ± 0.02, indicating the area is under high-stress condition. A significant variation is observed in the b value for the whole investigated region, where the value varies in four different spatial domains from west to east, respectively, as 0.56 ± 0.03, 0.93 ± 0.07, 0.83 ± 0.05, and 0.90 ± 0.08 from Chamoli (Garhwal region) to northwestern Nepal region. A significant change in b value with respect to time is also observed at which an abrupt decrease in b value was found after the occurrence of a moderate-size earthquake (i.e., ML > = 5), indicating high-stress accumulation. The Dc value of 1.84 ± 0.04 is observed for the region, which indicates the high level of material heterogeneity, owing to the presence of local faults and transverse tectonics and the presence of space-time clustering of seismicity in the area of investigation. The correlation integral analysis indicates a straight portion observed in the range between 8.81 and 41.1 km. The inference based on the spatial and temporal variation in b value and Dc value reveals a relative increase in recent seismic activity in regions A (Chamoli, Garhwal) and C (Dharchula–Pithoragarh–Munsiyari, Kumaun) compared to regions B (Kapkot–Bageshwar, Kumaun) and D (Far western Nepal side), with low b value due to decrease in the number of small-magnitude earthquakes probably indicating accumulation of high stresses in the region.

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Seismicity Analysis in Kumaun–Garhwal Himalaya: Earthquake Characteristics, b Value, and Multifractals

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  • 发表日期：

    2026年

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  • Santosh Joshi,
  • Rajeev Upadhyay

摘要

The present seismicity catalog of Kumaun–Garhwal Himalaya, which includes the local earthquake events between 1991 and 2018 with magnitude (ML: 1–6.5), has been investigated for understanding the spatial-depth pattern of seismicity coupled with the geotectonic setting of the region. Additionally, the spatiotemporal behavior of microseismicity has also been assessed by investigating the frequency-magnitude distribution (b value) and fractal dimension (Dc). The b value was calculated by using the entire magnitude range (EMR) method, while the Dc value was calculated by adopting the correlation integral method. The microseismicity in the region is mainly concentrated across the hinterland region, especially along the Main Central Thrust (MCT) zone, where most of the earthquakes are confined to shallow depths coincident with the depth of the Main Himalayan Thrust (MHT). The maximum likelihood estimates for the whole region provide the b value as 0.75 ± 0.02, indicating the area is under high-stress condition. A significant variation is observed in the b value for the whole investigated region, where the value varies in four different spatial domains from west to east, respectively, as 0.56 ± 0.03, 0.93 ± 0.07, 0.83 ± 0.05, and 0.90 ± 0.08 from Chamoli (Garhwal region) to northwestern Nepal region. A significant change in b value with respect to time is also observed at which an abrupt decrease in b value was found after the occurrence of a moderate-size earthquake (i.e., ML > = 5), indicating high-stress accumulation. The Dc value of 1.84 ± 0.04 is observed for the region, which indicates the high level of material heterogeneity, owing to the presence of local faults and transverse tectonics and the presence of space-time clustering of seismicity in the area of investigation. The correlation integral analysis indicates a straight portion observed in the range between 8.81 and 41.1 km. The inference based on the spatial and temporal variation in b value and Dc value reveals a relative increase in recent seismic activity in regions A (Chamoli, Garhwal) and C (Dharchula–Pithoragarh–Munsiyari, Kumaun) compared to regions B (Kapkot–Bageshwar, Kumaun) and D (Far western Nepal side), with low b value due to decrease in the number of small-magnitude earthquakes probably indicating accumulation of high stresses in the region.