Stress variations in southern Tonga slab derived from deep-focus earthquakes

0585722 - GFÚ 2025 RIV US eng J - Journal Article
Hrubcová, Pavla - Rastjoo, Ghazaal - Vavryčuk, Václav
Stress variations in southern Tonga slab derived from deep-focus earthquakes.
Journal of Geophysical Research-Solid Earth. Roč. 129, č. 5 (2024), č. článku e2023JB028039. ISSN 2169-9313. E-ISSN 2169-9356
R&D Projects: GA ČR(CZ) GA22-10747S
Institutional support: RVO:67985530
Keywords : stress inversion * Tonga slab segments * mantle transition zones * seismicity * sub-horizontal faults * focal mechanisms
OECD category: Volcanology
Impact factor: 3.9, year: 2022
Method of publishing: Open access
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023JB028039

Tonga is a convergent plate boundary between the Pacific and Australian plates and is the fastest and the most seismically active deep subduction system in the world. We focused on southern Tonga (south of latitude 22 degrees S) and the mantle transition zone (depths of 410-670 km), where seismic activity forms two subparallel bands of events in the east and west. We performed stress analysis by inverting focal mechanisms of earthquakes available in the Global Centroid Moment Tensor catalog and revealed two distinct stress regimes in the slab. While the stress orientation in the eastern slab segment conforms to the down-dip compressional stress along the entire slab, the stress orientation in the western slab segment is different, having the maximum compression in the vertical direction. This suggests that the western segment can represent a stagnant slab with flattening and bending, as proposed by modeling studies. Its connection with the younger actively subducting slab is supported by the horizontal westward shift at 520 km depth. The stress analysis also indicates substantially different fault orientations in both segments. In the actively dipping slab, the majority of activated faults are predominantly sub-horizontal. However, they are significantly inclined from vertical in the stagnant slab segment. A higher scatter in fault orientations in the stagnant slab suggests deformation, fragmentation and rheological complexity resulting from bending and flattening.
Permanent Link: https://hdl.handle.net/11104/0353438