Receiver-Fault Variability and Depth-Dependent Coulomb Stress Changes in the 2019 Mw 7.2 Halmahera Earthquake Sequence
DOI:
https://doi.org/10.70561/geocelebes.v10i2.47046Kata Kunci:
extensional area, receiver fault variability, seismic triggering, stress shadow, strike-slip kinematicsAbstrak
This study investigates the relationship between fault geometry, Coulomb stress transfer, and aftershock distribution in the Halmahera region after the 2019 Mw 7.2 Halmahera Earthquake. Analysis of focal mechanism solutions reveals two distinct clusters: Cluster 1 is located southwest of the mainshock around Bacan Island and is dominated by normal faulting that suggests local extension, whereas Cluster 2 trends southeast of the mainshock along southern Halmahera and exhibits a mix of strike-slip and normal. Coulomb stress modeling shows that when only the maximum ΔCFS across the depth column is considered, aftershocks appear to occur within positive stress-change zones (ΔCFS ≥ ~0.1 bar). Evaluation at the actual hypocentral depths reveals that many aftershocks are concentrated within zones of apparent stress-reduction at shallow levels (0–10 km). This observation may be due to mismatches in receiver-fault geometry, spatial heterogeneity in the background stress/strength field, or processes that are not captured by static ΔCFS. By applying a fault-variability approach, we demonstrate that small variations in receiver-fault orientation can substantially alter ΔCFS outcomes and better reproduce the observed aftershock distribution. These results underscore the importance of receiver-fault geometry and segmentation specific to the Halmahera region in interpreting stress transfer.
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