Surface displacements in Japan before the 11 March 2011 M9.0 Tohoku-Oki earthquake

Seismo-Deformation Anomalies Associated with the M6.1 Ludian Earthquake on August 3, 2014

“…Not only can be seen in the Ludian earthquake, this unique disorder-alignment-disorder sequence can also be found in other events around the Ludian area (Figure 6e). The unique sequence observed in this study also agrees with the observation in the previous studies [21][22][23][24]. However, earthquake occurrence does not follow the sequence and no event is detected after the sequence that can be found during the study period.…”

“…In this study, we found that the crustal deformation exhibits a disorder-alignment-disorder sequence of the GNSS-azimuths days before the Ludian earthquake in China. The sequence is similar to the observation of the seismo-deformation anomaly two months before the Tohoku-Oki earthquakes in Japan [23] and tens of days before several earthquakes in the Taiwan region [21,22,24]. An agreement between the orientations of the GNSS-azimuths and the direction of the maximum compressive axis of the two earthquakes suggests that the alignment is seismogenic.…”

“…The disorder-alignment-disorder sequence shown in Figure 6e can be repeatedly observed in the spatial domain in Figure 8. Meanwhile, the sequence (Figures 6e and 8) agrees with the observations of earthquakes in Japan and the Taiwan region [21][22][23][24]. again a few days before the Ludian earthquake.…”

“…The residual is generally considered to be the long-term trend of the time series with no significant frequency characteristics, while each IMF is considered as the instantaneous frequency and amplitude at each observed epoch. When using HHT to study the crustal deformation, the residual is the long-term plate tectonic movements [22,23], whereas the IMFs are the frequency-dependent components which represent the nature of the deformation with the long-term tectonic movements removed. The "filtered GNSS data" hereafter denotes the observed cGNSS deformation time series with the residual (the long-term tectonic movements) and the frequency-dependent IMFs (the frequency-dependent factors common to all stations such as annual, semi-annual and seasonal variations and noise) removed.…”

Very short-term earthquake precursors from GPS signal interference based on the 2013 Nantou and Rueisuei earthquakes, Taiwan

“…In last two decades, Global Positioning System (GPS) has been widely used as a tool to monitor earthquake precursors such as changes in the ionospheric total electron content (TEC) (Afraimovich and Astafyeva, 2008;De Agostino and Piras, 2011;Liu et al, 2010;Liu et al, 2001;Thomas et al, 2012;Zakharenkova et al, 2007) or the production of systematic residual crustal displacements after removing periodic ones (Chen et al, 2013;Chen et al, 2014). In this study, we report a new type of earthquake precursor, namely the L-band interference signals detected by high-rate, Continuous GPS receivers (CGPS).…”