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Microtremor Activity and Its Seismic Insights: A Focus on the Nagavalli and Vamshadara River Basin, Eastern Ghats,India.

Bandari N, Vijayaraghavan R.

JOURNAL OF THE GEOLOGICAL SOCIETY OF INDIA

https://doi.org/10.17491/jgsi/2025/174143 

This study investigates microtremor activity in the Srikakulam district of Andhra Pradesh, located within the tectonically active Eastern Ghats Mobile Belt (EGMB). Two clusters of low magnitude microtremors were recorded between Jan 2016, and Aug 2017 aligning with the NW–SE oriented Nagavali Fault and a NE–SW trending lineament. A total of 41 microtremors were recorded, suggesting potential fault reactivation under prevailing stress conditions. This implies that tectonic compressive stresses, combined with upper crustal mafic intrusions, may be causing near-critical stress along existing faults, thereby increasing seismic vulnerability. Notably, two past seismic events M3.8 (1985) and M3.3 (2008) occurred near the intersection of unnamed lineaments close to the Nagavalli and Vamshadara faults, and along another lineament, respectively. Additionally, site response analysis using the H/V spectral ratio method revealed significant ground motion amplification at Challavanipeta and Vennalavalasa seismic stations, with values reaching 5.8 and 6.4, respectively. The findings underscore the importance of continuous monitoring, improved infrastructure planning, and region-specific building codes to enhance earthquake preparedness in the EGMB region.

Seismicity map of Srikakulam district, Andhra Pradesh(Jan 2016 to Aug 2017). (insert map: seismic network) (map source: Bhukosh, GSI; Wessel et al., 2019).

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