## 3 Results and Discussion
### Comparison of GPS, Seismic and Integrated Waveforms  
We compare the integrated displacements with seismic-only waveforms obtained from double integration of raw acceleration data. The results of two collocated pairs AKT006/0183 and NGN017/0986 are shown in Figure 1 as an example. The left sub-figures show the entire period of the seismic shaking in north/east/up components at AKT006/0183, and the right ones show the seismic shaking at NGN017/0986 in the same three components. The GPS station 0183 (40.2154\({}^{\circ}\) N, 140.7873\({}^{\circ}\) E), which is located 251 km from the epicenter of Tohoku-Oki earthquake, is collocated with K-Net seismic station AKT006 (about 20 m away from GPS station), and the other pair NGN017 and 0986 station within 5 km distance, where the distance to the epicenter is about 480 km. The uncorrected seismic displacements are traditionally observed from zero-order corrected with only consideration removing the pre-event mean bias. Although the dynamic motions can be determined, a linear or parabolic drift is apparent in the latter part of each displacement time series, and the permanent coseismic offset is lost in a seismic-only solution. The corrected seismic displacements are derived from the baseline-corrected strong motion recordings which are processed using the automatic empirical baseline correction scheme proposed by [PERSON] [29]. Although the corrected seismic displacements have a high degree of similarity of the dynamic component with the integrated results, they still maintain several decimeter differences in permanent coseismic offsets due to the effect of the residual baseline bias error. From the integrated displacement waveforms, there are obvious permanent coseismic offsets which are about 0.47 m, 0.51 m, and 0.03 m in the north, east, and up components at station AKT006/0183, while the permanent offsets of station NGN017/0986 are relatively small, about 0.04 m in the north, 0.12 m in the east, and 0.01 m in the up components. It is demonstrated that the [PERSON]'s method is currently considered to be the most robust seismic-alone  
Figure 1: Comparison of uncorrected seismic-only and corrected seismic-only, and integrated displacements on the collocated AKT006 (seismic) and 0183 (GPS) pair and NGN017 (seismic) and 0986 (GPS) pair during the Tohoku-Oki earthquake on 11 March 2011. All sub-figures show the entire period of seismic shaking. The 100 Hz integrated displacement is shown by the red line. The 100 Hz seismic-only displacements without baseline correction and with baseline correction are respectively shown by the blue line and the black line, respectively. one [30], but more accurate displacements without offsets should be relied on the GPS-aided baseline correction method [11]. In Figures 2 and 3, we compare the tightly-integrated displacements (the red line) and GPS-only displacements (the black cross symbols). The results of the AKT006/0183 and NGN017/0986 pairs are respectively shown in the left and right side of Figure 2, and the similar results of the 5058/P496 and 5028/P744 pairs are also shown in Figure 3. The GPS station P496, which is located about 60 km from the epicenter of 2010 El Mayor-Cucapah earthquake, is collocated with SCSN seismic station 5058 (about 70 m separation). The other pair P744 and 5028 station are within 140 m of each other, and the distance from them to the epicenter is about 65 km. All sub-figures from top to bottom depict the entire period of seismic shaking in north, east and up components. We can see that the integrated displacements are in good agreement with GPS-only solution in terms of peak displacements, permanent offsets and long-period stability. However, it is clearly shown that the GPS-only displacements are with lower sampling rate and higher noise compared to the integrated displacements. The root mean square (RMS) values of GPS-only solution (10 min pre-event displacement series) are 1.1, 1.1 and 3.0 cm respectively in north, east and vertical components.