GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake

Y Otsuka,T Maruyama,T Ogawa,S Saito,N Kotake,T Tsugawa,Effendy Effendy,T Komolmis,M Kawamura,N Hemmakorn,K Shiokawa

doi:10.1186/bf03353373

Abstract

Abstract We report the response of the ionosphere to the large earthquake that occurred in West Sumatra, Indonesia, at 0058 UT on December 26, 2004. We have analyzed Global Positioning System (GPS) data obtained at two sites in Sumatra and at three sites in Thailand to investigate total electron content (TEC) variations. Between 14 and 40 min after the earthquake, TEC enhancements of 1.6–6.9 TEC units (TECU) were observed at subionospheric points located 360–2000 km north of the epicenter. From the time delays of the observed TEC enhancements, we find that the TEC enhancements propagated northward from the epicenter. The time delays between the earthquake and rapid increases in TEC, which occurred near the epicenter, are consistent with the idea that acoustic waves generated by the earthquake propagated into the ionosphere at the speed of sound to cause the TEC variations. A small TEC enhancement of 0.6 TECU was observed south of the epicenter, while no TEC enhancements were seen east of the epicenter. From a model calculation, we find that this directivity of the TEC variations with respect to the azimuth from the epicenter could be caused partially by the directivity in the response of the electron density variation to the acoustic waves in the neutral atmosphere.

Highlights

Atmospheric and ionospheric disturbances following impulsive forcing on the ground, such as earthquakes, volcanic eruptions, and powerful explosions, have been observed with various techniques (e.g., Ogawa et al, 1982; Blanc, 1985; Kanamori et al, 1994; Igarashi et al, 1994)
The other three receivers were installed at Chumphon (10.7◦N, 99.4◦E), Bangkok (13.7◦N, 100.8◦E), and Chiang Mai (18.8◦N, 98.9◦E) in Thailand by the National Institute of Information and Communications Technology (NICT), King Mongkut’s Institute of Technology Ladkrabang, and Chiang Mai University
Total electron content (TEC) along a ray path from a Global Positioning System (GPS) satellite to a receiver is precisely obtained from the carrier phase delays, a level of the total electron content (TEC) is unknown because of an unknown initialization constant in phase measurements

Summary

Introduction

Atmospheric and ionospheric disturbances following impulsive forcing on the ground, such as earthquakes, volcanic eruptions, and powerful explosions, have been observed with various techniques (e.g., Ogawa et al, 1982; Blanc, 1985; Kanamori et al, 1994; Igarashi et al, 1994). These impulsive sources generate vertical displacement of the atmosphere at the earth’s surface, exciting atmospheric infrasonic acoustic waves. The vertical oscillations of the bottomside ionosphere measured by HF-Doppler sounders have been reproduced in model calculations which simulate acoustic gravity waves propagating from the ground to the ionosphere (Artru et al, 2004)

Results

Discussion

Conclusion