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Abstract
A unique atmospheric wave was recorded by a monostatic sound detection and ranging (sodar) system operating at Vapi, India (20.37° N, 72.90° E), on 25 January 2001 prior to the Bhuj, India, earthquake that jolted India on 26 January 2001. This precursory wave was the largest amplitude (480 m) and lowest frequency wave (70.02 μHz) ever recorded at 25 sodar operational sites in India/Maitri, Antarctica, in the past 30 years. It appears to be an Acoustic Gravity Wave (AGW) propagating in the lower atmosphere, and this precursory signature may support the hypothesis of AGW generation prior to a major earthquake.
Acknowledgements
The authors would like to thank the field staff and the authorities of M/S Sabaro Organics Limited, Vapi, India, for permitting us to use the data for this research. In addition, the authors would like to express their gratitude to Prof. Harsh K. Gupta for valuable discussions and encouragement. Thanks are also due to the authorities in the DST, New Delhi, for supporting our project proposal to establish sodars in seismically active zones in India.