Large-scale rift-related faulting linked to a caldera-forming eruption: A case study from Taupō, New Zealand

Résumé fourni par la source

Intra-arc rifts are regions of extensional tectonics and magmatic processes, which can interact and lead to both earthquakes and volcanic activity. We examine the temporal and spatial relationships between the ~35 km 3 (magma), caldera-forming, 232 CE ± 10 CE eruption from Taupō volcano of the Taupō Volcanic Zone and slip on the adjacent Whakaipō Fault. The spatio-temporal distribution of fault throw is examined through paleoseismic trenching coupled with remote and field-based analyses of the fault scarp and deformed post-eruptive paleoshorelines intersected by this structure. Along the Whakaipō Fault, throw increases towards the volcano, reflecting the role of Taupō volcano in localising fault strain. Paleoseismic trenching exposes an un-degraded paleoscarp with a ~ 50° slope draped by 232 CE fall deposits, implying that fault slip occurred no more than days to months prior to the eruption. Analysis of fault and paleoshoreline displacements at Whakaipō Bay on the northern Lake Taupō shoreline suggest that two main phases of Whakaipō Fault slip occurred after the eruption: (1) an ‘aftermath’ phase, occurring over a ~ 20-year period after the eruption, during which 10 ± 1.2 m of throw was accrued locally on the fault; and (2) a ‘longer-term’ phase through to the present day, during which 2.8 ± 0.3 m of fault throw has accrued. Faulting during the aftermath phase is estimated to account for ~78 % of the total extension accommodated locally (adjacent to the caldera) on the Whakaipō Fault since the 232 CE eruption. Our observations suggest that caldera-forming eruptions in the TVZ can be associated with complex, volcano-tectonic (i.e., rifting) sequences that feature both pre-eruptive and highly localised, post-eruptive, decametre-scale displacement on caldera-adjacent rift faults.

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