Abstract
The precursory processes detected from unambiguous and repeatable instrumental observations that precede an earthquake remain elusive despite the multiple types of pre-earthquake signals gained from observations of geo-electricity, geomagnetism, and electromagnetism. Recently, much attention has been paid to associate abnormal behaviors of TEC (total electron content) in ionosphere, with seismic forcing. In this paper, we examined ionospheric TEC variations 1 - 2 weeks preceding 20 moderate to great earthquakes (M = 5 - 8) in the Tibetan Plateau and its neighboring regions between 1999 to 2008, with the help of a nationwide continuously-tracking GPS network. The temporal and spatial TEC variations over the specific seismogenic zones were calculated, and the causal linkage between the identified TEC anomalies and these earthquakes was examined. We find that most of the earthquakes showed significant abnormalities with similar characteristics. The anomalies, either upper anomalies (85%, 17/20) or lower anomalies (65%, 13/20) occurred in the ionosphere with dimensions of 30° in latitude and 30° in longitude above the epicenters. It is noted that the ionospheric anomalies were more dependent on focal depths of earthquakes than their magnitudes. Our results suggest that these anomalies of TEC may be possible seismoionospheric signatures for the earthquakes in Tibet and its margins.
Highlights
When Leonard and Barnes (1965) first showed that some level of ionospheric disturbances had preceded strong earthquakes, many studies have demonstrated unambiguously that a large earthquake ruptured the surface of the Earth, and disturbed the atmosphere and ionosphere (Leonard and Barnes 1965; Weaver et al 1970; Hayakawa and Fujinawa 1994; Liu et al 2000; Pulinets et al 2000; Popov et al 2004; Liperovskaya et al 2006; Yu et al 2009)
In order to gain a robust insight into the ionospheric precursor of an earthquake, we examined abnormal variations in the local ionosphere for earthquakes which occurred in the Qinghai-Tibet region from 1999 to 2008, of which 20 major events were investigated
We studied the ionospheric anomalies associated with 20 earthquakes occurred in Qinghai-Tibet region by examining the GPS-inferred TEC variations
Summary
When Leonard and Barnes (1965) first showed that some level of ionospheric disturbances had preceded strong earthquakes, many studies have demonstrated unambiguously that a large earthquake ruptured the surface of the Earth, and disturbed the atmosphere and ionosphere (Leonard and Barnes 1965; Weaver et al 1970; Hayakawa and Fujinawa 1994; Liu et al 2000; Pulinets et al 2000; Popov et al 2004; Liperovskaya et al 2006; Yu et al 2009). Abnormal variations in the local ionosphere for earthquakes which occurred in the Qinghai-Tibet region from 1999 to 2008, of which 20 major events were investigated. We classified these earthquakes in terms of their magnitudes, focal depths and corresponding ionospheric parameters (TEC), and tried to associate spatio-temporal variations in the TEC value with the earthquakes of interest. We found that the repeated anomalies preceded most of the earthquakes. We discussed the possibility that the ionospheric anomalies were used as the precursors of the earthquakes
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