On mitigation of earthquake and landslide hazards in the eastern Himalayan region.

Mitigation of geological hazards through science and engineering applications is one of the most effective ways to reduce their impact on human life and local infrastructure. It involves precise mapping of hazards, assessment of their potential, monitoring, early warning, geotechnical treatment, design of vital infrastructural facilities and creating awareness at local levels. Several such initiatives have been taken at government level to deal with the earthquakes and landslides in the eastern Himalayan region. These efforts facilitated identification of potential areas and sites, susceptible to future events and helped in improving our understanding of crustal structure, geodynamics, tectonics, seismogenesis, and soil properties, etc. The paper highlights details of the major initiatives, significant achievements, and priorities to help in better mitigation of earthquake and landslide hazards in the eastern Himalayan region.

A source and ground motion study of earthquakes in and near Delhi (the National Capital Region), India.

We study source parameters of 10 local earthquakes (2.7 ≤  M w ≤ 4.5) that have occurred in the National Capital Region (NCR) since 2001 and the ground motions produced by these events. Moment rate spectra of the earthquakes retrieved from the recordings at hard sites after applying corrections for geometrical spreading (1/R, R ≤ 100 km), anelastic attenuation (Q = 253f 0.8) and cutoff frequency (f m = 35 Hz) are reasonably well fit by the Brune ω 2-source model with stress drop ranging between 0.9 and 13 MPa. Neglecting the outlier low-stress drop value, the average stress drop is 6 MPa. We apply a modified standard spectral ratio technique to estimate site effect at 38 soft sites in the NCR as well as the geometrical mean site effect with respect to a reference hard site. Application of the stochastic method, with source characterized by the Brune ω 2- model with stress drop of 6 MPa and the mean site effect for soft sites, yields peak horizontal ground acceleration and velocity curves that are in good agreement with the observed values. These results provide the parameters needed for the application of the stochastic method to predict ground motions at hard and soft sites in the NCR during postulated M w ≤ 5.5 earthquakes.

A holistic seismotectonic model of Delhi region.

Delhi region in northern India experiences frequent shaking due to both far-field and near-field earthquakes from the Himalayan and local sources, respectively. The recent M3.5 and M3.4 earthquakes of 12th April 2020 and 10th May 2020 respectively in northeast Delhi and M4.4 earthquake of 29th May 2020 near Rohtak (~ 50 km west of Delhi), followed by more than a dozen aftershocks, created panic in this densely populated habitat. The past seismic history and the current activity emphasize the need to revisit the subsurface structural setting and its association with the seismicity of the region. Fault plane solutions are determined using data collected from a dense network in Delhi region. The strain energy released in the last two decades is also estimated to understand the subsurface structural environment. Based on fault plane solutions, together with information obtained from strain energy estimates and the available geophysical and geological studies, it is inferred that the Delhi region is sitting on two contrasting structural environments: reverse faulting in the west and normal faulting in the east, separated by the NE-SW trending Delhi Hardwar Ridge/Mahendragarh-Dehradun Fault (DHR-MDF). The WNW-ESE trending Delhi Sargoda Ridge (DSR), which intersects DHR-MDF in the west, is inferred as a thrust fault. The transfer of stress from the interaction zone of DHR-MDF and DSR to nearby smaller faults could further contribute to the scattered shallow seismicity in Delhi region.

Evaluation, effect and utilization of submarine groundwater discharge for coastal population and ecosystem: A special emphasis on Indian coastline.

Submarine groundwater discharge (SGD) is an important process driven by marine and terrestrial forces. Low tide affects SGD the most, therefore the ideal time to detect SGD is the low tide, especially during spring tide. Techniques to detect and quantify SGD along with the understanding of the related aquifer characteristics is discussed in this study. Scientific community across the world is realizing the importance of studying and mapping SGD because in the scenario of climate change, this part of the global hydrological cycle is an important process and is known to have a significant effect on the marine ecosystem due to nutrient and metal inputs around the region of discharge. Therefore, understanding the processes governing SGD becomes very important. In this review, various components and processes related to SGD (e.g. Submarine Groundwater Recharge, Deep Porewater Upwelling, Recirculated Saline Groundwater Discharge), along with detailed discussion on impacts of SGD for marine ecosystem is presented. Also, it highlights the future research direction and emphasis is put on more research to be done keeping in mind the changing climate and its impacts on SGD.