Abstract:In the past 200 years, the Kachchh paleorift in western India, a plate interior region, has witnessed unusually large number of strong earthquakes, namely, the 2001 Bhuj (Mw 7.6), 1956 Anjar (Mw 6.0), 1845 Lakhpat (Mw ~6), and 1819 Allah Bund (Mw ~7.7) earthquakes. We report continuous GPS measurements from the Kachchh and adjoining region. We find that the ongoing deformation during 2009–2016 is inconsistent with the models of postseismic deformation due to the 2001 Bhuj earthquake. The current widespread def… Show more
“…Also, a slower moving Marwar Craton would lead to compression across the Kachchh failed rift (figure 8 ), which would be consistent with the GPS measurements across the Kachchh failed rift (Gahalaut et al . 2019 ). Figure 8 A schematic cartoon showing the Marwar and Bundelkhand cratons modified after Vijaya Rao et al .…”
Section: A Hypothesised Tectonic Model For Seismogenesis In the Adfbmentioning
The Aravalli–Delhi Fold Belt (ADFB) is one of three prominent ridges on the continental part of the Indian plate extending northward from central India and subducting beneath the Himalayan arc. Though it is seismogenic along its entire NE–SW structural trend, activity varies spatially with a noteworthy region of higher seismicity in the vicinity of Delhi. We analyse historical and modern instrumented seismicity. Using recomputed focal mechanisms for events such as the 1956 Bulandshahr earthquake, we found that the maximum principal stress (
σ
1
) in this region is oriented in the N–S to NE–SW direction, similar to that in the neighbouring Garhwal–Kumaun Himalayas. Our analysis also indicates that the earthquakes along the ADFB occur on steep faults which are parallel or oblique to its NE–SW structural trend and that the entire crust appears to be seismically active as the earthquakes occur up to a depth of ~40 km. Within the better instrumented Delhi region, we observed a pattern in the average monthly frequency of earthquakes recorded that we speculate was modulated by monsoonal recharge of the local water table. The cause of seismicity in the AFDB is still a question for debate, pending better seismological and geodetic instrumentation, but we build on evolutionary models of the ADFB to suggest that seismicity is the consequence of the continued relative motion between the Bundelkhand and Marwar cratons in the northern Indian shield. The nature and causes of earthquakes in this region notwithstanding, the proximity of large cities such as Delhi, Jaipur and Udaipur to poorly-studied or unknown sources of seismic hazard is a concern and warrants further scientific and policy intervention.
Supplementary Information
The online version contains supplementary material available at 10.1007/s12040-022-01957-3.
“…Also, a slower moving Marwar Craton would lead to compression across the Kachchh failed rift (figure 8 ), which would be consistent with the GPS measurements across the Kachchh failed rift (Gahalaut et al . 2019 ). Figure 8 A schematic cartoon showing the Marwar and Bundelkhand cratons modified after Vijaya Rao et al .…”
Section: A Hypothesised Tectonic Model For Seismogenesis In the Adfbmentioning
The Aravalli–Delhi Fold Belt (ADFB) is one of three prominent ridges on the continental part of the Indian plate extending northward from central India and subducting beneath the Himalayan arc. Though it is seismogenic along its entire NE–SW structural trend, activity varies spatially with a noteworthy region of higher seismicity in the vicinity of Delhi. We analyse historical and modern instrumented seismicity. Using recomputed focal mechanisms for events such as the 1956 Bulandshahr earthquake, we found that the maximum principal stress (
σ
1
) in this region is oriented in the N–S to NE–SW direction, similar to that in the neighbouring Garhwal–Kumaun Himalayas. Our analysis also indicates that the earthquakes along the ADFB occur on steep faults which are parallel or oblique to its NE–SW structural trend and that the entire crust appears to be seismically active as the earthquakes occur up to a depth of ~40 km. Within the better instrumented Delhi region, we observed a pattern in the average monthly frequency of earthquakes recorded that we speculate was modulated by monsoonal recharge of the local water table. The cause of seismicity in the AFDB is still a question for debate, pending better seismological and geodetic instrumentation, but we build on evolutionary models of the ADFB to suggest that seismicity is the consequence of the continued relative motion between the Bundelkhand and Marwar cratons in the northern Indian shield. The nature and causes of earthquakes in this region notwithstanding, the proximity of large cities such as Delhi, Jaipur and Udaipur to poorly-studied or unknown sources of seismic hazard is a concern and warrants further scientific and policy intervention.
Supplementary Information
The online version contains supplementary material available at 10.1007/s12040-022-01957-3.
“…We deduce that the higher displacement rate in the flanks is mainly responsible for the accumulation of more strain in the central part of KRB and the presence of high seismicity towards the central part of KRB supports our deduction. A study (Gahalaut et al, 2019) found a good correlation between geodetic moment rate and seismic moment release rate. Furthermore, an accumulation of maximum strain of 5 nano-strain/ year is observed in the vicinity of the 2001 earthquake epicentre (Dumka et al, 2019).…”
Section: Grace Observationsmentioning
confidence: 98%
“…The outliers were down-weighted from the generated time-series (Figure S1) to obtain a consistent set of coordinates for the velocity estimation. Furthermore, the results of (Dumka et al, 2019;Gahalaut et al, 2019) were jointly analysed with the results of present study.…”
Section: Gnss Observationsmentioning
confidence: 99%
“…Furthermore, the long‐term compression (≈4 mm/year from north and south) of the Kachchh region has been estimated (Dumka et al, 2019; Gahalaut et al, 2019) based on the continuous mode Global Positioning System (GPS) dataset for almost 8 years of ISR (Institute of Seismological Research) which is less as compared to the Indian plate boundary region (Ader et al, 2012; Bisht et al, 2020; Calais et al, 2006; Dixon et al, 1996; Dumka, Chodhury, Gahalaut, et al, 2018; Dumka, Kotlia, Kumar, & Satyal, 2014; Dumka, Kotlia, Kumar, Satyal, & Joshi, 2014; Dumka, Kotlia, SuriBabu, et al, 2018; Jade et al, 2014, 2017; Mazzotti, 2007; Sella et al, 2007).…”
The current geodetic investigation is based on nearly a decade of continuous Global Positioning System (GPS) data towards the western part of the Indian Plate (2009–2019). This research focused on the Kachchh Rift Basin (KRB), the seismically most active intra‐plate region of the Indian Plate, which has seen three ≥ M 7.0 earthquakes in the last two centuries. The GPS stations on the northern and southern margins show SSW and NNE directed motion, indicating that the KRB is currently under the influence of regional compressive stress on both flanks and the same is reflected in the form of earthquake activity in the center portion. Furthermore, the existence of intra‐basin stress, in addition to regional stress, increases strain accumulation and results in the creation of a Principal Deformation Zone (PDZ) in the central part of the KRB. The average annual deformation in the middle of KRB remains 1.0 ± 0.5 mm/year, while sites near the South Wagad Fault (SWF) experience 1.2 mm/year of fault parallel motion. The dominant fault normal motion along the flanks with a maximum fault parallel motion in the middle intimates the existence of strike‐slip tectonics in the central Kachchh. The geometric relationship of strike‐slip faults in a compressive margin and strain accumulation in pre‐existing faults (PDZ) is responsible for current strike‐slip and thrust motion in the Kachchh, including the 2001 Bhuj earthquake (M 7.7). Our geodetic model is well‐corroborated with the geological observations of the wrench fault model of strike‐slip faults. PS‐InSAR results in the northern part of the region between Khadir and Bela Islands show ≤6.0 mm of annual LOS displacement. GPS results indicate ≈ 1.3 to 1.4 ± 0.5 mm/year of fault parallel motion along the transverse Ekal Amrapar Fault (EAF). The non‐significant variation in GRACE‐derived TWS values (from 2009 to 2018) rules out non‐tectonic deformation in the vicinity of EAF and thus points to tectonic activity as the cause of the derived deformation in the region.
“…Dumka et al (2018) proposed that even a very small reservoir can influence the deformation and may antrigger earthquake. Gahalaut et al (2019) analysed the crustal deformation across the Kuchchh paleo rift to suggest that the paleo-rift is under excessive compression.…”
We provide a short overview of the seismological research conducted by the Indian researchers pertaining to the Indian subcontinent, during the past five years. This synthesis primarily includes results of studies on crustal architecture, geodynamics, seismotectonics and earthquake source parameters. An appraisal of the earthquake monitoring networks in India is also provided.
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