Timing of coseismic displacement grid model construction for updating the semi-kinematic reference frame: case study in Taiwan

Construction of a coseismic displacement grid model (hereafter referred to as the grid model) is a critical strategy for maintaining the precision of the semi-kinematic reference frame. However, no unequivocal criteria have yet been suggested for the timing of grid model construction. To clarify this timing, the observations of continuous global navigation satellite system in Taiwan were evaluated using coordinate time series analysis from 2003 to 2018 and a horizontal precision of approximately 14 mm was proposed as the threshold to construct a grid model. Next, two strategies were proposed to evaluate the timing on the basis of earthquake information. For Strategy I, the possible maximum surface displacement was derived using the forward dislocation model based on the hypocenter, moment magnitude and focal mechanism solution provided by the Real-Time Moment Tensor Monitoring System. For Strategy II, a required minimum magnitude (RMM) checking grid was constructed using the hypocenter and local magnitude data from the Central Weather Bureau, Taiwan. If the forwarded maximum surface displacement from Strategy I is larger than the threshold of 14 mm or the local magnitude of an earthquake is larger than the RMM from Strategy II, it represents the timing for the grid model construction. On the basis of the validation results for 20 selected earthquakes, both two strategies were proposed to be implemented simultaneously for timing evaluation to avoid overlooking detectable events.