## 1 Introduction  
Precise point positioning (PPP) is a global navigation satellite system (GNSS) positioning method to calculate precise positions at centimeter- or even millimeter-level accuracy with a single GNSS receiver using precise satellite orbit and clock products [1; 2]. Over the past decades, PPP using Global Positioning System (GPS) has been proved as an effective approach for the measurement of arbitrarily large ground motions and seismic displacements induced by earthquakes [3; 4; 5; 6; 7]. BeiDou Navigation Satellite System (BDS) began to offer positioning, navigation, and timing services in the Asia-Pacific region at the end of 2012. It is aimed at serving global users upon its completion by 2020. Many studies have been conducted to investigate the performance of BDS precise positioning. With three geostationary Earth orbit (GEO) and three inclined geosynchronous orbit (IGSO) satellites, [PERSON] et al. [8] demonstrated that precise relative positioning at an accuracy of 1-2 cm in horizontal and 4 cm in vertical components can be obtained in short baseline mode (\(\sim\)436 m). [PERSON] et al. [9] presented an initial assessment of the positioning performance of BDS. Using BDS observations, they showed that the accuracy of BDS kinematic relative positioningwas comparable to that of GPS kinematic positioning, exhibiting a root mean square (RMS) of 3, 3, and 6 mm in the east, north, and vertical components, respectively. Meanwhile, intensive attention is also paid to PPP with BDS-only observations. [PERSON] et al. [10] and [PERSON] et al. [11] realized static and kinematic PPP at centimeter-level accuracy by using BDS observations at a sampling interval of 30 s. [PERSON] et al. [12] assessed the contributions of BDS GEO, IGSO, and medium Earth orbit (MEO) satellites to PPP in Asia-Pacific region. By using various combinations of different satellite constellations, they showed that BDS IGSO has the largest contribution to the acceleration of convergence and improvement of positioning accuracy to PPP, particularly in the east component. Recently, [PERSON] et al. [13] presented that the real-time BDS PPP mode with an accuracy of 5 cm in horizontal and 10 cm in vertical components could be obtained after 3 h convergence. Moreover, BDS has played an important role in high-precision applications, such as the derivation of the zenith tropospheric delay [14] and the capture of seismic waves. [PERSON] et al. [15] first used 1 Hz BDS observations to measure ground motions induced by the 2015 Mw 7.8 Gorkha, Nepal earthquake. They employed the variometric approach to estimate the velocity time series and to reconstruct displacements by integrating the velocity time series. A novel approach of a linear trend removal was performed to minimize long-period drifts due to mismodeling of different intervening effects during integration to displacements. However, none of the previous studies has been conducted on the monitoring of seismic displacements/waveforms using the BDS PPP approach. With the BDS PPP approach, the seismic displacements are able to be derived directly. As a consequence, the procedure of integration, a requirement of the variometric approach, is successfully circumvented. The availability of precise satellite orbit and clock products is of great importance to the realization of PPP. For the GPS constellation, the International GNSS Service (IGS) is able to routinely provide final products containing satellite orbits and clocks with an accuracy of \(\sim\)2.5 cm and \(\sim\)75 ps, respectively (see [[http://igs.org/products](http://igs.org/products)]([http://igs.org/products](http://igs.org/products))).