Termination Time Anomalies in Subionospheric VLF Transmitter Signals During Indonesian Earthquakes of 26 December, 2004 (Tsunami) and 28 March, 2005

摘要

Termination time technique has been employed to process the amplitude data of 19.8 KHz (NWC)subionospheric VLF transmitter signals monitored at Agra (Lat. 27.2°N, Long. 78°E), India, usingAbsPAL receiver for the period between 1 December, 2004 and 15 April, 2005. The results show thatthere are considerable shifts in sunrise and sunset termination times during the earthquakes of 26December, 2004 (M = 9.1, tsunami) and 28 March, 2005 (M=8.5) which occurred nearly at the sameplace in the Indonesian region. These results are supported by a statistical analysis of the data whichhas been carried out using mean (m) and standard deviation (σ) approach. Some possible physicalmechanisms which may be responsible for the observed anomalies are discussed.