Abstract
This study employed two-dimensional principal component analysis (2DPCA) for the detection of anomalies in the two-dimensional ionospheric total electron content (TEC) associated with Japan three earthquakes and earthquake-induced tsunamis. From 04:40 to 04:50 (UTC) on February 15th, first TEC precursor was detected over the epicentre of the 16 February quake with the duration time of at least 10 minutes. A weak TEC anomaly associated with an earthquake-induced tsunami was also detected from 23:15 to 23:20 (UTC) on 16 February with the duration time of at least 5 minutes. An additional earthquake (Mw = 6.3) occurred in Miyako in the vicinity of the first earthquake. Second TEC precursor to the 20 February Miyako earthquake was recorded over the epicentre between 10:20 and 10:30 (UTC) on 19 February with the duration time of at least 10 minutes. A supplemental earthquake occurred (Mw = 6.1) as well in Miyako in the vicinity of the first earthquake. A TEC precursor to the 21 February Miyako earthquake was recorded over the epicentre between 04:15 and 04:25 (UTC) on 20 February with the duration time of at least 10 minutes. The three Miyako earthquakes presented similar anomalies and duration time in the TEC fluctuations, due largely to similarities in the magnitudes of the largest principal eigenvalues and the close proximity of the epicentres. Our results led to the reasonable confirmation that the very weak TEC anomaly following the Miyako earthquake on 16 February was associated with the earthquake-induced tsunami. 2DPCA is a useful mathematical tool for the monitoring of anomalous ionospheric fluctuations for use in the early warning of weak tsunamis.
Highlights
Natural precursors to earthquakes have been studied widely (Kamogawa 2006; Rishbeth 2006; Dautermann et al 2007; Yasuda et al 2009; Astafyeva, Heki 2011)
total electron content (TEC) anomalies associated with the two Miyako earthquakes and the subsequent tsunamis could not be identified using the largest principal eigenvalues
A TEC precursor was detected for the Miyako earthquake occurred at 23:06:27 (UTC) on 15 February 2015 for a period of 10 minutes from 04:40 to 04:50 (UTC) on 15 February 2015
Summary
Natural precursors (e.g. electric signals) to earthquakes have been studied widely (Kamogawa 2006; Rishbeth 2006; Dautermann et al 2007; Yasuda et al 2009; Astafyeva, Heki 2011). A study by Akhoondzadeh and Saradjian (2011) used the interquartile method, wavelet transformation, and Kalman filter method to identify the TEC anomaly (decreased TEC) that appeared at 19:00 (LT) on 11 January before the Haiti earthquake. The research by Liu et al (2011a) showed that a TEC anomaly with increased TEC appeared in relation to the Haiti earthquake and persistently in a small region of the northern epicentre area. These previous studies suggested that both increased and decreased TEC could not be standard indicators of ionospheric anomalies related to earthquakes.
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