On 31 March 2002, a M_L= 6.8 earthquake (called the "331 earthquake") occurred in northeastern Taiwan off Hualien. The shock lasted over 30 seconds across the entire island of Taiwan. The earthquake caused a few centimeters of coseismic deformation, and a few centimeters of ground motion in the northern and eastern parts of Taiwan. All of these displacements have been recorded by the Taiwan Continuous GPS Array (TCGA), and estimated by two different post-processing methods, namely the daily solution and the kinematic positioning algorithm. Precise evaluation of the coseismic deformation and capturing instantaneous ground motion at a level of just millimeters requires rigorous computational procedures. In this paper, a completely regular algorithm to estimate the crustal deformation in the Taiwan area has been applied to acquire coseismic deformation as a result of the 331 earthquake. A set of high sampling rate (1 Hz) data from the TCGA has been used to study simultaneous ground motion during the 331 earthquake. Using over 18 months of data and 100 stations of the TCGA, the coseismic deformation due to the 331 earthquake can be precisely estimated, and instantaneous ground motion can be observed in that portion of the TCGA network where stations with high sampling rate observations are situated. Since the coseismic deformation can be acquired precisely and the instantaneous ground motion can be computed by continuous GPS observations and integrated with seismic data, these results can aid the study of seismology and earthquake geodesy.