A study of the behavior of the terminator time shifts using multiple VLF propagation paths during the Pakistan earthquake (M = 7.2) of 18 January 2011
Abstract
On 18 January 2011, at 20:23 UTC, an earthquake of magnitude 7.2 occurred in south-western Pakistan (latitude 28.73(°) N, longitude 63.93(°) E) at a depth of 68 km. We present the results of the analysis of very low frequency (VLF) radio signals, received at three stations located in India. We analyze the VLF signals around this earthquake day and look for possible precursory effects of this earthquake. For our analysis, we use four different VLF propagation paths. These propagation paths are DHO-IERC (Sitapur), VTX-Pune, VTX-ICSP (Indian Centre for Space Physics, Kolkata) and NWC-IERC. We observed significant shifts of the “sunrise terminator time” (SRT) for DHO-IERC and VTX-Pune paths. For DHO-IERC path, the SRT of the VLF signals shifted towards night time three days before the earthquake day, and in the case of VTX-Pune path it shifted towards night time just one day before the earthquake day. For VTX-Kolkata path, the shift of SRT is four days before the earthquake day, but here the shift is not so strong, somewhere between 2sigma and 3sigma lines. For the other two paths, namely, DHO-IERC and VTX-Pune, the terminator time shifts crossed the 3sigma line. We found no significant shifts of SRT for NWC-IERC propagation path. Higher deviation in the VTX-Pune path as compared to VTX-ICSP path could be due to the proximity of the former to the epicenter. Similarly, DHO-IERC path is over the epicenter while NWC-IERC path is totally away from the epicenter. This could be the reason why the effect in DHO-IERC path is stronger than that in NWC-IERC path.
- Publication:
-
40th COSPAR Scientific Assembly
- Pub Date:
- 2014
- Bibcode:
- 2014cosp...40E2711R