## 3 Experiments and Results
### Application in the 2017 Ms 7.0 Juzhaigou Earthquake  
The 2017 Ms7.0 Juzhaigou earthquake occurred in Sichuan Province of China at 3:19:46 (UTC) on August 8. The epicenter was at 33.20\({}^{\circ}\) N, 103.82\({}^{\circ}\) E, and the focal depth was about 20 km. After the main shock, a large number of aftershocks occurred successively in the epicenter area, some of which reached a magnitude of 4.0. This earthquake became another magnitude 7.0 earthquake in the eastern part of the Bayan Har block after the 2013 Lushan Ms 7.0 earthquake. In the near-field area of the Juzhaigou earthquake, these motions were successfully recorded by several 1 Hz high-rate GNSS observation stations of the GNSS data product service platform of the China Earthquake Administration, and several 200 Hz SM accelerometer observation stations of the China Earthquake Networks Center, National Earthquake Data Center. These seismic monitoring networks provide a large amount of available data to validate the effectiveness and robustness of the proposed method for broadband co-seismic deformation. To monitor the crustal co-seismic deformation by integrating GNSS and SM data, GSMX and 62 MXT are selected as GNSS/SM co-located stations for analysis. The high-rate GNSS and SM station information is shown in Table 2. During the experiment, the data processing time is from 13:19:52 to 13:21:07 (UTC) on 8 August 2017 with a total of 75 s. The observation process is simulated in real time, and the final displacement results are converted into north-south, east-west, and upward directions. For SM, baseline shifts can be broadly categorized into two groups: baseline shift before the event and baseline shift caused by the event [2]. Theoretically, the acceleration observations should be close to zero before the earthquake wave arrives. However, due to the initial bias caused by unadjusted instruments and ambient temperature changes, the recorded value is nonzero before the event. The resulting error (i.e., initial baseline value) would lead to the integral displacement drift severely if it is not corrected before the event. Therefore, in this study, the first 10 s of basic accelerations are used to estimate the initial baseline value, which is subtracted from the subsequent recordings to remove the baseline shift before the event. Figure 3 shows the acceleration, velocity, and co-seismic displacement time series of 62 MXT stations after prior baseline correction during the earthquake in north-south, east-west, and upward directions. In Figure 3, the velocity is supposed to gradually recover to near zero after the violent shake, but there is some deviation in the actual result due to the ground inclination and rotation. On the other hand, the integral displacement should be fixed at a certain value, but in the second half of the displacement time series, severe drifts occur. From the above analysis, it can be concluded that the original SM acceleration observations not only have the baseline shift before the event, but also contain the baseline shift caused by the event. Therefore, aiming to correct the baseline shift during the earthquake, high-rate GNSS displacement is introduced as an external constraint for data calibration and fusion. Figure 4 shows the displacement results from 6 s after the main shock. The inspections from this figure highlight the following. (1) The presented VC-AKF has the ability to eliminate the baseline shift caused by the event in real time and better consistency with the GNSS results. Moreover, there is no drift or divergence phenomenon throughout the earthquake, and accurate permanent displacements can be derived. (2) Compared with GNSS, the surface co-seismic deformations can be described in more detail by the proposed VC-AKF. Specifically, the overall trend of the integrated data is constructed by the GNSS displacement, while the details are expressed by the SM acceleration with higher sampling