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

ABSTRACT The Eastern Ghats Mobile Belt (EGMB) along India’s eastern coast is a tectonically active region characterized by complex geological structures and seismic activity, which necessitates detailed seismic hazard assessments for effective risk mitigation. This study investigates the microtremor activity observed in the Srikakulam district of Andhra Pradesh from January 2016 to August 2017, where two distinct clusters of microtremors were identified near Etcherla town and near Annapuram village of Nandigam Mandal. Analysis reveals that these microtremor events correspond to known fault orientations, prominently the NW-SE-oriented Nagavali Fault and an unnamed NE-SW-oriented lineament. The clustering of events along structural discontinuities suggests potential fault reactivation under existing stress conditions. Additionally, the study explores site response through the horizontal-to-vertical (H/V) spectral ratio method, identifying significant ground motion amplification at Challavanipeta and Vennalavalasa, with amplification values around 5.8 and 6.4, respectively. These high amplification levels, likely attributed to thick sedimentary deposits, indicate a substantial seismic hazard, drawing parallels with amplification zones in the Bhuj region, which faced extensive damage during the 2001 earthquake. This study enhances the understanding of seismic hazards in the EGMB, particularly in the Srikakulam district, emphasizing the importance of continuous seismic monitoring for effective hazard assessment and mitigation.