Noida, located within India's National Capital Region and near the tectonically active Himalayan region, is highly susceptible to seismic activity. Past moderate to high-intensity seismic events emphasize the need for detailed subsurface characterization to enhance seismic hazard assessments. This study investigates seismic site effects in Noida using microtremor measurements and the Nakamura technique to develop spatial distribution maps for seismic amplification, fundamental frequency, and seismic vulnerability index. A total of 129 microtremor data points were collected, with 54 meeting the SESAME criteria for reliable Horizontal-to-Vertical Spectral Ratio (HVSR) analysis. The analysis reveals that the predominant frequency at most sites falls within the range of 0.63-1.10 Hz, indicating the widespread presence of thick, soft sediments in the area. To avoid structural damages caused by the resonance of soil and structure and a table is prepared to showcase the approximate building frequency of various storey in order to avoid soil-building resonance phenomenon. The maximum amplification (A(0)) observed ranges from 4.53 to 5.17 at a few sites, whereas the majority of the study area experiences low to moderate amplification. The calculated seismic vulnerability index (K-g) for the 54 studied locations ranges from 2.27 to 23.60, with higher values found in regions with soft alluvial deposits, identifying them as fragile zones likely to suffer infrastructure damage during an earthquake. Lower K-g values correspond to areas with stiffer substrates. This study provides a preliminary assessment for urban planning and highlights the need for further research into the socio-economic and structural seismic vulnerabilities of the Noida region.

Electronics and other anthropogenic sources of noise in urban environments interfere with the early time signals of traditional transient electromagnetic (TEM) surveys due to the mutual inductance effect of transmitter and receiver coils. This poses problems for the detection of shallow geohazards such as karst dissolution features that lead to the subsidence and subsequent damage to infrastructure. The opposing-coils transient electromagnetic method (OCTEM) provides an alternative to traditional TEM surveys that is less sensitive to anthropogenic noise, and which is applied in this study to characterize shallow geohazards in a residential area responsible for subsidence and ground collapse. An investigation in Xiacun Town, China, was supplemented by ground-penetrating radar (GPR), drilling, and groundwater level monitoring to verify the OCTEM results and develop a conceptual model relating site hydrogeological factors to the ground collapse. OCTEM accurately identified shallow Quaternary gravel aquifers across the study area. However, OCTEM failed to identify additional subsidence structures near the collapsed pit demonstrated by the GPR results or the presence of a large, soil-filled cave below the pit determined from drilling. The site was concluded to be at further risk of subsidence and ground collapse associated with groundwater erosion driven by extreme precipitation events and excessive groundwater abstraction.