Abstract
Since October 1, 2010, a GPS receiver is put into operation at Tokai (Japan) in an experiment on Neutrino Physics (T2K). A significant variation of the altitude was detected from the beginning of March 2011, so that it has made worthwhile to investigate the possibility that such variations could be correlated to the Tohoku earthquake. In order to investigate in details this possibility, we analyzed the GPS data collected during 2011 by GEONet the GPS Earth Observation Network (GEONET). GEONET is the GPS network of Japan and consists of 1240 permanent stations. Preliminary results of the analysis seemed to show ten days before the earthquake, some possible anomalous behaviors of the stations. These anomalous behaviors were particularly relevant for stations of the network near the epicentral area. While co-seismic and post-seismic variations are widely expected, the anomalies recorded about ten days before the earthquake could be seriously considered among short-term precursors of the earthquake. In order to confirm this possibility, more detailed studies have been performed. In particular, GEONET currently makes available only daily solutions of the stations coordinates. On the contrary, it is very important to improve the time resolution just to understand the features of the anomalies till the last hours before the Earthquake. For this reason, we have performed an analysis to evaluate the coordinates and movement on hourly basis so improving the time resolution.
Highlights
A wide variety of natural phenomena are detrimental for the natural environment and for the anthropic structures and the human being
After the preliminary step in which we have analyzed the daily solution provided by GPS Earth Observation Network (GEONET), we have, as second step, unwrapped the data to perform their reprocessing in order to achieve hourly solutions and, improve the time resolution in order to understand if abrupt events or discontinuities have been occurred during the investigated period
Co-seismic effect is related to a large decrease of heights that occurs on the day of earthquake, while no other variation appears before or after the earthquake
Summary
A wide variety of natural phenomena are detrimental for the natural environment and for the anthropic structures and the human being. The most recent results show that seismic precursors can be divided into two different categories: ground precursors [1,2,3,4], and atmospheric precursors [5]. The ground precursors are highlighted by means of on-ground measurements while atmospheric precursors are revealed by satellites [5,6]. We present the possibility of investigating one of the main ground precursors, i.e. the crustal deformation. The heights are evaluated by means of GPS technique and in this sense such ground precursors are monitored by means of satellite techniques. The height data refer to different geographical areas of Japan and the data analysis as revealed possible preseismic, coseismic and postseismic effects in the crustal altitude
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