How do plate boundaries talk to each other in North Sulawesi, Indonesia?

Fault interactions are associated with stress transfer. In many tectonic settings the actual extent of stress transfer and thus interaction is poorly understood, especially on the time scale of the seismic cycle. The tectonic setting in North Sulawesi hosts two major fault systems that are closely tied: the Minahassa subduction interface connects directly to the strike-slip Palu-Koro fault. Both these seismogenic interfaces have also generated tsunamis. Through 20+ years of GNSS monitoring, two events of fault interactions have been recorded. The first event is the notion of increased relative motion across the Palu-Koro fault following the 1996 M_w7.9 Minahassa subduction earthquake [Walpersdorf et al. 1998]. The second event is the notion of transient slip accumulating to M_w6.7 on the Minahassa subduction interface following the 2018 M_w7.5 Palu-Koro strike-slip earthquake [Nijholt et al. 2024].

 

We seek to understand the mechanical coupling across the tectonic system in North Sulawesi through numerical finite element models. The manner in which tear faults connect to subduction interfaces at depth is unknown. We define the geometry by taking the Slab2.0 [Hayes et al. 2018] topology of the Minahassa slab and abutting it against the Palu-Koro fault at its western termination. We drive deformation kinematically to investigate whether a strike-slip earthquake on the Palu-Koro fault can generate slip on the subduction interface. In particular, we seek to determine whether varying the viscosity of the fault zones at depth and mantle wedge can explain the slip ‘delay’ at the Minahassa interface; observations indicate that the slow slip peak activity occurred 340 days after the 2018 earthquake in an event that took over 10 months.

 

 

Hayes, G.P., Moore, G.L., Portner, D.E., Hearne, M., Flamme, H., Furtney, M., Smoczyk, G.M., 2018. Slab2, a comprehensive subduction zone geometry model. Science 362 (6410), 58–61. https://doi.org/10.1126/science.aat4723.

Nijholt, N. Simons, W.,Riva, R., Efendi, J. Sarsito, D., Broerse, T., 2024. Triggered and recurrent slow slip in North Sulawesi, Indonesia, Tectonophysics, 10.1016/j.tecto.2024.230416, 885, (230416)

Walpersdorf, A., Vigny, C., Subarya, C., Manurung, P., 1998. Monitoring of the Palu- Koro Fault (Sulawesi) by GPS. Geophys. Res. Lett. 25 (13), 2313–2316.