S. J. Shan

Bio: S. J. Shan is an academic researcher from National Central University. The author has contributed to research in topics: Total electron content & TEC. The author has an hindex of 1, co-authored 1 publications receiving 395 citations.

Pre-earthquake ionospheric anomalies registered by continuous GPS TEC measurements

Abstract: . In this paper we examine pre-earthquake ionospheric anomalies by the total electron content (TEC) derived from a ground-based receiver of the Global Positioning System (GPS). A 15-day running median of the TEC and the associated inter-quartile range (IQR) are utilized as a reference for identifying abnormal signals during all of the 20M≥6.0 earthquakes in the Taiwan area from September 1999 to December 2002. Results show that the pre-earthquake ionospheric anomalies appear during 18:00–22:00LT (LT=UT+8h) within 5 days prior to 16 of the 20M≥6.0 earthquakes. This success rate of 80% (=16/20%) suggests that the GPS TEC is useful to register pre-earthquake ionospheric anomalies appearing before large earthquakes. Key words. Ionosphere (ionospheric disturbances; ionosphere-atmosphere interactions)

A statistical investigation of preearthquake ionospheric anomaly

Abstract: [1] Empirical evidence of the preearthquake ionospheric anomalies (PEIAs) is reported by statistically investigating the relationship between variations of the plasma frequency at the ionospheric F2 peak foF2 and 184 earthquakes with magnitude M ≥ 5.0 during 1994–1999 in the Taiwan area. The PEIA, defined as the abnormal decrease more than about 25% in the ionospheric foF2 during the afternoon period, 1200–1800 LT, significantly occurs within 5 days before the earthquakes. Moreover, the odds of earthquakes with PEIA increase with the earthquake magnitude but decrease with the distance from the epicenter to the ionosonde station. These results indicate that the PEIA is energy related.

Seismoionospheric GPS total electron content anomalies observed before the 12 May 2008 Mw7.9 Wenchuan earthquake

Abstract: [1] The global ionospheric map (GIM) is used to observe variations in the total electron content (TEC) of the global positioning system (GPS) associated with 35 M ≥ 6.0 earthquakes that occurred in China during the 10-year period of 1 May 1998 to 30 April 2008. The statistical result indicates that the GPS TEC above the epicenter often pronouncedly decreases on day 3–5 before 17 M ≥ 6.3 earthquakes. The GPS TEC of the GIM and electron density profiles probed by six microsatellites of FORMOSAT3/COSMIC (F3/C) are further employed to simultaneously observe seismoionospheric anomalies during an Mw7.9 earthquake near Wenchuan, China, on 12 May 2008. It is found that GPS TEC above the forthcoming epicenter anomalously decreases in the afternoon period of day 6–4 and in the late evening period of day 3 before the earthquake, but enhances in the afternoon of day 3 before the earthquake. The spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions, respectively. The F3/C results further show that the ionospheric F2 peak electron density, NmF2, and height, hmF2, significantly decreases approximately 40% and descends about 50–80 km, respectively, when the GPS TEC anomalously reduces.

Ionospheric Precursors of Earthquakes; Recent Advances in Theory and Practical Applications

Abstract: This paper accumulates the recent advances in scientific understanding of the problem of seismo-ionospheric coupling. Present research focuses on three main areas: the physical mechanism, main phenomenological features of ionospheric variations associated with earthquakes, and their statistical properties permitting use of them in practical applications. In this paper, the developed physical model bridges the traditional precursors of earthquakes and ionospheric ones, demonstrating that the latter belong to the same family. In this regard the earthquake preparation zone is key generating the scaling law and the relationship between geochemical precursors, anomalous electric field involved in ionospheric variations initiated, and the ionospheric irregularities themselves. Revealed ionospheric precursor phenomena and their statistical parameters are used to develop a pattern recognition technique and other statistical processing techniques that can be used in short-term earthquake prediction. Finally a possible system of ground based measurements and satellite monitoring is proposed for regional and global monitoring and possible short-term prediction of destructive earthquakes.