Variability of repeating earthquake behavior along the Longitudinal Valley fault zone of eastern Taiwan

Two major clusters of repeating earthquake sequences (RES) are found on two fault patches near the Longitudinal Valley fault (LVF) in eastern Taiwan, the Chihshang segment to the south and the Hualien segment to the north. The 25 M 2.3-4.6 RES on the Hualien segment are widely distributed in a NNE direction over a distance of 45 km, whereas on the Chihshang segment, the 30 M 2.2-3.4 RES have a shorter along-strike extent of about 15 km. The longer spatial extent of RES on the Hualien segment may indicate a wider distributed creeping zone at depth. M >= 3.8 RES are observed on the Hualien segment and are characterized by quasiperiodic recurrence. Statistical analysis of the size and number of earthquakes adjacent to the RES indicates that the smaller number of large earthquakes in the vicinity may explain the quasiperiodic recurrence of RES. We argue that on the Hualien segment, M similar to 4 or larger earthquakes are isolated enough in space to facilitate the occurrence of repeated ruptures.