Earthquake Interactions in Central Taiwan: Probing Coulomb Stress Effects Due to ML≥ 5.5 Earthquakes From 1900 to 2017

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Though large efforts have been made in studying earthquake generation processes, earthquake triggering in central Taiwan is still not well understood. The occurrence of 14 mainshocks with ML≥ 6.0 from 1900 to 2017 and the presence of eight active fault systems provide excellent data sets for studying earthquake interaction in central Taiwan. We examined the coseismic Coulomb stress changes (ΔCFSs) due to mainshocks in the sequence and other surrounding earthquakes comprising 3 smaller magnitude mainshocks with 5.5 ≤ML≤ 6.0 and 25 aftershocks with ML≥ 5.5. When considering only triggering effects from mainshocks in the sequence, the compounded ΔCFSs are significant for all 13 mainshocks with 8 being promoted (ΔCFS > 0.1 bar) and 5 being inhibited (ΔCFS < −0.1 bar). After adding effects from other surrounding earthquakes, we found that five mainshocks were promoted and seven were inhibited. Yet it is questionable whether the 2016 mainshock was promoted, because the calculated uncertainties at the hypocenter might reduce ΔCFS below the 0.1 bar triggering threshold. In addition, significant positive ΔCFSs (>2 bars) on the Chukou, Chaochou, and Chishan faults and flat decollement of central Taiwan suggest failure promotion on those active faults. Contrarily, significant negative ΔCFSs (<−0.2 bar) on the Changhua, Shungtung, Chelungpu, and Hsinhua faults suggest that ruptures on those faults might be inhibited. We also conducted sensitivity studies indicating uncertainty level of 33–38% of the calculated ΔCFSs. Our findings indicate that preceding earthquakes have affected nucleation and rupture propagation of large earthquakes in central Taiwan during the past 120 years.

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