Testing the influence of static and dynamic stress perturbations on the occurrence of a shallow, slow slip event in eastern Taiwan

We report the first evidence for the detection of a slow slip event in the Longitudinal Valley, in eastern Taiwan. The slow event, which lasted about 3.5days, has been detected by borehole strainmeters. It occurred at shallow depths (about 2 to 4km), either on the Longitudinal Valley Fault or on the Central Range Fault. Here we investigate whether the event occurrence was influenced by transient and periodic stress perturbations, in particular by the June 2013 M-w 6.2 Nantou earthquake, which occurred about 60km away and 6days prior to the event. Modeled changes in Coulomb stress in the direction parallel to the geologic slip vector on the fault planes show negative static stress changes (approximately -1.5 to -1kPa), while maximum dynamic stress changes generated by the surface waves are ranging from 5.5 to 14.5kPa. We also observe that the slow event initiated during a maximum of Earth and ocean tidal Coulomb stress changes (about 0.8 to 1.5kPa). Dynamic and static stress perturbations represent a few percents to tens of percents of the stress buildup through the slow rupture cycle. However, the absence of recurrent events during the 12years of strain monitoring (2006 to 2018) prevents to estimate the recurrence interval of the slow event, which limits our ability to further interpret the link between the rupture and the perturbations. Finally, there is no large and unique load transient at the time of the initiation, therefore this single event may have likely occurred spontaneously.