Changes in paleostress and its magnitude related to seismic cycles in the Chelung-pu Fault, Taiwan

Paleostress analysis was conducted through a multiple stress inversion method using slip data recoded for the core samples from the Taiwan Chelung-pu Fault Drilling Project (TCDP). Two stress fields were obtained; one of these had horizontally plunging σ₁, and the other has horizontally plunging σ₂ or σ₃ in the compressional stress direction of the Chi-Chi earthquake. Stress magnitude for both the stress fields was constrained by stress polygons, which indicated larger SHmax for horizontally plunging σ₁ than that in the case of horizontally plunging σ₂ or σ₃. These differences in stress orientations and stress magnitude suggest that the change in stress filed can be caused by stress drop and stress buildup associated with seismic cycles. The seismic cycles recoded in the core samples from TCDP could include many events at geological timescale and not only the 1999 Chi-Chi earthquake.