Distribution of b‐values in Indo‐Burma Ranges, northeast India: Implications to structural heterogeneities and style of faulting

Abstract

The spatial distribution of the b‐value has been determined using a homogeneous earthquake catalogue from 1964 to 2018 to examine the characteristics of structural heterogeneities and their bearing on the style of faulting in the Indo‐Burma region of Northeastern India. The study region is associated with an uneven distribution of structural heterogeneities and demonstrates the mixed type of faulting, nature where the majority of earthquakes resulted mainly by thrust and strike‐slip fault. Our critical analysis demonstrates that the existence of two prominent zones is associated with high b‐values and low b‐values where the mixed type of faulting resulted in the genesis of seismicity in the study area. The high b‐values in the study area contain a large number of smaller earthquakes whilst the low b‐values comprise a smaller number of larger earthquakes distributed along with the Naga‐Disang Thrust, Kabaw Fault, and Sagaing fault systems. A close comparison between b‐values and different faulting styles reveals that the area containing a low b‐value suggests stronger seismogenic zones, where an accumulation of strain energy leads to the genesis of seismicity by thrust faulting with slight slip component whilst Indo‐Burma Ranges regions connected with b‐values (0.5–0.9) demonstrate strike‐slip to the normal mode of faulting, indicating relatively weak seismogenic zones where tensional forces are prevalent. The depth sections illustrate that lower b‐values for the upper part of the subducting slab correspond to more stress generated by tectonics compared to that of the lower part, and interestingly the deeper part of the subducting Indian slab is coupled with conspicuously very high‐b values, suggesting the weakening of the Indian subducting slab through dehydration.

Spatio‐temporal variation in b‐value prior to the 26 November 2021 Mizoram earthquake of northeast India

“…Khan et al (2011) reported a variation in the b ‐value from 0.23 to 1.78 for entire northeast India. Likewise, Bora et al (2018) and (2021) reported the spatial disparity of the b ‐value for the IBR region from 0.70 to 1.50. In the present study, the low b ‐value of 0.84 is reported for the grid lying between 25°–27° N and 94°–96° E while the maximum b ‐value of 1.51 is reported for the grid lying between 23°–25° N and 96°–98° E.…”

Introduction, Part 2—Geodynamic evolution of Eastern Himalaya and Indo‐Myanmar orogenic belts: Advances through interdisciplinary studies

“…In the paper by Bora, Borah, et al (2022), the spatial distribution of the b ‐value has been determined using a homogeneous earthquake catalogue from 1964 to 2018 to examine the characteristics of structural heterogeneities and their bearing on the style of faulting in the Indo–Burma region of North‐eastern India. A close comparison between b ‐values and different faulting styles reveals that the area containing a low b ‐value suggests stronger seismogenic zones, where an accumulation of strain energy leads to the genesis of seismicity by thrust faulting with slight slip component whilst Indo–Burma Ranges regions connected with b ‐values (0.5–0.9) demonstrate strike‐slip to the normal mode of faulting, indicating relatively weak seismogenic zones where tensional forces are prevalent.…”

“…This Special Issue‐ Part 2 is a continuation of earlier Special Issue‐ Part 1 published in vol. 57 (2), of Geological Journal , which contained 26 research articles (Ao & Satyanarayanan, 2022; Baral et al, 2022; Bhowmik et al, 2022; Bora, Borah, et al, 2022; Bora, Mukherjee, et al, 2022; Deb & Ray, 2022; Devi & Singh, 2022; Devrani et al, 2022; Doley et al, 2022; Gogoi et al, 2022; Gupta et al, 2022; Hazarika & Kayal, 2021; Imtisunep et al, 2022; Liu et al, 2022; Luirei et al, 2022; Lukram & Tandon, 2022; Bidyananda et al, 2022; Majumdar, Gogoi, & Ghatak, 2022; Majumdar, Gogoi, Ghatak, Saikia, et al, 2022; Mukherjee et al, 2022; Pebam et al, 2021; Rashid et al, 2022; Saikia et al, 2022; Singh and Kshetrimayum, 2021; Singh, Guruaribam, Singh et al, 2022; Singh, Singh, Singh, et al, 2022; Srivastava, 2021; Srivastava & Kichu, 2021). Figure 2 displays the area of study of 29 papers included in this Special Issue 2.…”

“…Geological map of Eastern Himalaya, Indo‐Myanmar orogenic belt, northern, Central Myanmar, and adjacent areas (modified after Mitchell et al, 2007; Searle et al, 2007; Y. R. Singh, Singh, Singh, et al, 2022). Locations of study area presented in the issue include 1/S2: Kundu and Hazarika (2022); 2/S2: Y. R. Singh, Singh, Singh, et al (2022); 3/S2: Rawat and Luirei (2022); 4/S2: Kayal et al (2022); 5/S2: Choudhury et al (2022); 6/S2: N. M. Sharma et al (2022); 7/S2: Goswami, Gogoi, et al (2022); 8/S2: Bikramaditya et al (2022); 9/S2: Goswami, Kalita, et al (2022); 10/S2: Joshi (2022); 11/S2: Jha and Sharma (2022); 12/S2: Shukla et al (2022); 13/S2: Khonglah et al (2022); 14/S2: Ali and Duarah (2022); 15/S2: Mohanty et al (2022); 16/S2: Chanu et al (2022); 17/S2: Majumdar, Gogoi, and Ghatak (2022); Majumdar, Gogoi, Ghatak, Saikia, et al (2022); 18/S2: Ding et al (2022); 19/S2: Ghose et al (2022); 20/S2: Hussain and Dey (2022); 21/S2: Ozukum et al (2022); 22/S2: Jamir et al (2022); 23/S2: Chaubey et al (2022); 24/S2: Bora, Borah, et al (2022); Bora, Mukherjee, et al (2022); 25/S2: Khuman and Ibotombi (2022); 26/S2: Y. R. Singh, Singh, Singh, et al (2022); 27/S2: Thokchom and Kshetrimayum (2021); 28/S2: Barman et al (2022); 29/S2: V. Sharma and Biswas (2022)…”