EGU24-16276, updated on 09 Mar 2024
https://doi.org/10.5194/egusphere-egu24-16276
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Triggered and recurrent slow slip in North Sulawesi, Indonesia

Nicolai Nijholt1,2, Wim Simons2, Taco Broerse3, and Riccardo Riva3
Nicolai Nijholt et al.
  • 1Utrecht University, Faculty of Geosciences, Earth Sciences, Utrecht, Netherlands (n.nijholt@uu.nl)
  • 2Delft University of Technology, Faculty of Aerospace Engineering, Astrodynamics and Space Missions, Delft, Netherlands
  • 3Delft University of Technology, Faculty of Civil Engineering and Geosciences, Geoscience and Remote Sensing, Delft, Netherlands

Nearby faults interact with each other through the exchange of stress. However, the extent of fault interaction is poorly understood. In particular, closely tied tectonic systems like crustal-scale faults that are right next to subduction zone interfaces are likely to express such interactions. Interactions may lead to slow-slip activity, resulting in episodes of transient surface motion.

Our study concentrates on Northwest Sulawesi (Indonesia), which hosts two fault zones with potential for major earthquakes and tsunamis: the strike-slip Palu-Koro fault and the Minahassa subduction zone. Both fault zones accommodate 4 cm/yr of interseismic relative motion. Thanks to a 20-year-long effort in geodetic monitoring, we are able to identify multiple periods during which surface velocities deviate from their interseismic trend. The most recent episode followed the 2018 Mw7.5 Palu earthquake.

We use a Bayesian methodology with forward predictions of slip on the two fault interfaces to match the observations following the 2018 Mw7.5 Palu earthquake, and infer that both deep afterslip on the Palu-Koro fault and slow slip on the Minahassa subduction interface have caused the observed transient surface motion. This finding represents the first recording of a slow slip event on the Minahassa subduction interface. We also speculate that the subduction interface and the strike-slip fault are likely interacting on a regular basis, affecting the seismogenic potential of both parts of this tectonic system.

How to cite: Nijholt, N., Simons, W., Broerse, T., and Riva, R.: Triggered and recurrent slow slip in North Sulawesi, Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16276, https://doi.org/10.5194/egusphere-egu24-16276, 2024.