1. Introduction

The International Association of Seismology and Physics of the Earth’s Interior (IASPEI) is one of the eight Associations of the International Union of Geodesy and Geophysics (IUGG), dedicated to promotion of international cooperation and coordination of scientific studies in the field of seismology, Earth’s internal structure and Tectonophysics. The Indian National Science Academy (INSA) is the National Adhering body representing India in the IUGG. INSA submits a National Report to the IUGG during its General Assembly, held every four years. The report consists of major scientific studies related to the eight Associations of the IUGG, carried out in the country during the preceding four years. The present chapter is a compilation for the IASPEI based on the scientific activities carried out in the country during 2019-2022, in the field of seismology.
    The present chapter briefly lists major contributions from India during the reporting period in the realm of IASPEI. Many R&D Institutes and Academic Departments in the country pursue seismological research. The National Center for Seismology under the Ministry of Earth Sciences (MoES), Government of India, is the nodal agency for monitoring and reporting earthquake activity in the country. It has got a network of more than 150 broadband seismological stations spread across the country. In addition to this, several seismological networks are operated by R&D Institutes under CSIR, DST, MoES and State Government of Gujarat, and Academic departments under IITs and IISERs, mainly for region-specific seismological research. These are briefly covered in Section 10.
    The chapter has been prepared based on the inputs received from many researchers belonging to these Institutes/Departments. However, it is not an exhaustive review of all the Indian contribution to seismology and allied fields during this period. The chapter is arranged to categorize the contributions under internal structure of the Indian lithosphere and sub-lithospheric mantle, crust and upper mantle deformation, seismic attenuation, seismic hazards, triggered seismicity, environmental seismology, paleoseismology and seismological networks. In addition, the chapter includes activities related to societal projects and outreach programs.

2. Seismological Imaging of the Indian Lithosphere and Mantle

2.1 Indian Shield Region

Inversion of receiver functions (RF) revealed that the Deccan Volcanic Province (DVP) and the Eastern Dharwar Craton (EDC) have distinct crustal structure in terms of crustal thickness, average composition, shear wave velocity variation and nature of the crust-mantle boundary (Kumar S., et al., 2020). Using a similar methodology, Gupta and Kumar (2022) estimated the thickness of the lithosphere beneath EDC and DVP and found it to be \(\sim\)50–60 km thinner in the DVP compared to that in the EDC. Arjun et al. (2022) carried out a joint modelling of teleseismic travel-time residuals, Bouguer gravity anomaly and surface topographic data to delineate the nature of the continental lithosphere beneath the Archaean Dharwar craton along an ENE-WSW traverse and reported an estimate of the Te and its role in supporting the topographic loads imposed by the Western Ghats, located near the western margin of the Southern Indian shield.
    Rao and Ravi Kumar (2022a) studied the crustal and uppermost mantle structure of the Western Ghats (WG) by slant stacking, common conversion point imaging and harmonic decomposition of RFs. Their results reveal a large crustal thickness of \(\sim\) 45 km in the central part of the WG, which decreases to \(\sim\) 39 km in the southern and \(\sim\) 37 km in the northern parts. The RFs also reveal a strong sub-Moho low velocity layer. By jointly inverting receiver function and surface wave group velocity dispersion, Mandal et al. (2022a) found that the Moho depth ranges from 39.5 to 42 km, while the lithospheric thickness varies from 108 to 120 km across 6 stations beneath the Palghar region in Maharashtra. Inversion of receiver functions from a network of 10 stations in the vicinity of Hyderabad revealed a 4-layered crust with a 16-km-thick high-velocity lowermost crustal layer, a 9-km-thick upper crustal layer with a Vp of 6.27 km/s, a middle and upper lower crust between 9–22 km depth (Mandal et al., 2022c). The modelled Moho depths vary from 35.4 to 37.6 km across the region.
    During 2013-2017, CSIR-NGRI maintained a seismic network of 15 three-component broadband stations in the Eastern Indian Craton (EIC). Results from joint inversion of receiver functions and surface wave group dispersion show a marked crustal thinning of 5–10 km and a ∼ 90 km thick lithosphere below the Singhbhum-Odisha-Craton (SOC), with a flat crust having a thickness of 42 km below the Chotanagpur Granitic Gneissic Terrain (CGGT) (Mandal, 2019a). A marked crustal and lithospheric thinning beneath SOC is also seen (Mandal et al., 2021). In addition, this study showed a relatively smaller degree of crustal (2–4 km) and lithospheric thinning (4–10 km) beneath the Eastern Ghat Mobile Belt, south of the SOC. Despite a thick crust, they note a 15–20 km lithospheric thinning associated with the CGGT. Based on results from H-K stacking and CCP imaging, a secular variation of the Archean crust formation is inferred in the Eastern Indian Shield (Mandal, 2022a). They observed a correlation between crustal age and composition within the ellipsoidal Paleoarchaean cratonic domain in the SOC. In analogy with the Paleoarchaean and Mesoarchaean granite-greenstone terrains such as the eastern Pilbara, Barbeton, and Kappvaal cratons, Mandal et al. (2021) suggested that crust formation during the Paleoarchaean SOC may have involved a thick oceanic mafic plateau followed by polybaric melting resulting in pulses of felsic magmatism with concurrent gravitational reorganization via Rayleigh Taylor Instabilities.
    A similar study indicated crustal and lithospheric thinning beneath Kachchh, along with a 2-6% reduction of Vs across the Lithosphere-Asthenosphere-Boundary (Mandal, 2019b). Local earthquake tomography of the Kachchh rift zone (Mandal, 2020a, 2022b) showed two prominent high-velocity anomalies within the crust which were attributed to mafic plutons. Paul H., et al. (2021) estimated the crustal thickness and uppermost mantle velocity beneath the Gujarat region using Moho-reflected phases and found that the Kachchh region has a thicker crust (43 km) owing to a root and high uppermost mantle velocity.
    Pn (Illa et al., 2021a) and Sn tomography (Illa et al., 2021b) of the Indian Shield and adjacent regions reveals that the upper mantle of the Indian shield is characterized by a Pn velocity of 8.12–8.42 km/s, while a large part of the central Indian shield has a higher mantle-lid velocity of \(\sim\) 8.42 km/s with a dominant anisotropic value of \(\sim\) 7.5% amounting to a variation of 0.2–0.3 km/s (Fig.1).