GPS Seismo-ionospheric Disturbances and Behaviors Following the 2011 Tohoku and 2008 Venchuan Earthquakes

S. Jin, R. Jin

Abstract:	Recently, a number of fatal earthquakes have frequently occurred at the Pacific Rim and SE Asia, such as Mw=8.1 Wenchuan Earthquake in 2008 and Mw=9.0 Tohoku Earthquake in 2011, which killed thousands of lives and generated huge tsunamis. Space geodetic techniques, such as Global Positioning System (GPS), could provide unique insights on the kinematic rupture and the size of these earthquakes, but monitoring and understanding the detailed Earthquake processes are still challenging issues due to the lack of denser near-field observations. Nowadays, GPS has been successfully used to remotely sense the atmosphere and ionosphere. The refracted signals from GPS Radio Occultation satellites together with ground GPS observations can provide the high precision tropospheric and ionospheric parameters, such as total zenith tropospheric delay (ZTD), total electron content (TEC) and electron density profile as well. The ground air waves from ground vertical motion of seismic and tsunami waves propagating may affect atmospheric disturbances. The high resolution and accuracy atmospheric sounding from ground and space based GPS will provide new opportunity to investigate atmospheric and ionospheric signals or behaviors before, during or after the earthquake. Since the first time Calais and Minster (1995) after the earthquake in California on 17 January 1994 observed the TEC anomalous signal in the period range 3-10 min, numerous studies have been trying to look for co-seismic or pre-seismic ionospheric anomalies. In this paper, GPS ionospheric disturbance behaviors and coupling with solid-Earth are investigated and compared following recent bigger earthquakes, Mw=8.1 Wenchuan Earthquake in 2008, March 9 Mw=7.2 and March 11 Mw=9.0 Japan earthquakes in 2011. The dense GPS network observation data are collected from China national continuous and campaign GPS network (CNCCN) and Japan GPS Earth Observation Network (GEONET), and the co-/pre-/post-seismic ionospheric disturbances are investigated from GPS-derived TEC time series around these events. Each i-th element of the vertical TEC is denoted by the measured TEC value I(t) at the time t. Duration of TEC time series depends on the time span when the GPS-satellite is in the zone of a corresponding receiver’s radio visibility. We filtered TEC series dI(t) by removing the trend with a time window of 5-20 min in order to show characteristic ionospheric disturbances. The filtered TEC variations during the mainshocks are investigated and significant co-seismic ionospheric disturbances are found at continuous GPS sites within 500 km from these epicenters. In order to determine propagation dynamics of the ionospheric disturbance, a simple interferometric method D1 and the quasi-optimum algorithm (QOA) method are used to determine the angular characteristics of the wave vector and phase velocity of ionospheric disturbances due to the earthquakes. For the 2008 Mw=8.1 Wenchuan earthquake, we found that an intensive N-shape shock-acoustic waves with a plane waveform and with half-period of about 200 sec propagated toward northeast with a mean velocity 600 m/s for a distance of about 1000 km from the epicenter, in parallel with the rupture direction. The far-field TEC effects are very small, e.g., South Korea and Japan. The properties of coseismic ionospheric response are determined by the geodynamics of the Wenchuan Earthquake. While the driving mechanism may be due to the acoustic coupling effect of the atmosphere and solid-Earth with air wave propagation from the ground to the ionosphere. Furthermore, the co-seismic tropospheric anomalies during the mainshock are also found, mainly in the zenith hydrostatic delay component (ZHD), which is supported by the same pattern of surface observed atmospheric pressure changes at co-located GNSS site that are driven by the ground-coupled air waves from ground vertical motion of seismic waves propagating. Therefore, the co-seismic atmospheric disturbances indicate again the acoustic coupling effect of the atmosphere and solid-Earth with air wave propagation from the ground to the top atmosphere. In addition, the GPS ionospheric disturbances following the March 9 Mw=7.2 and March 11 Mw=9.0 Japan earthquakes in 2011 are found using the denser GPS array observations in Japan. Results show pre-seismic ionospheric anomalies for both cases, while the magnitude of previous anomaly is much smaller than the latter one. Significant co-seismic ionospheric disturbances are also found for two cases with about 0.2~0.5TECU. The most propagation directions of co-seismic ionospheric disturbances are parallel to the rupture direction of the earthquakes. Furthermore, different seismo-ionospheric behaviors and patterns are presented and discussed. The significant seismic ionospheric disturbances are possibly driven by the ground-coupled air waves from ground vertical motion of seismic waves propagating with acoustic coupling effect of the atmosphere and solid-Earth. In the future, more information or details are needed to be further investigated, such as the coupling processes and mechanism of the seismo-ionospheric TEC variations.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	69 - 76
Cite this article:	Jin, S., Jin, R., "GPS Seismo-ionospheric Disturbances and Behaviors Following the 2011 Tohoku and 2008 Venchuan Earthquakes," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 69-76.
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