Three-dimensional crustal structure in the Southern Alps region of New Zealand from inversion of local earthquake and active source data

P and S‐P arrival time data from 311 earthquakes and several thousand offshore and onshore shots have been used in simultaneous inversion for hypocenters, three‐dimensional (3‐D) Vp and Vp/Vs models in the Southern Alps region, New Zealand. The combined data result in a highly nonuniform ray path di...

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Bibliographic Details
Published in:Journal of Geophysical Research: Solid Earth 2002-10, Vol.107 (B10), p.ESE 15-1-ESE 15-20
Main Authors: Eberhart-Phillips, Donna, Bannister, Stephen
Format: Article
Language:English
Subjects:
Alpine fault
crustal root
gravity
seismic tomography
Southern Alps
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Summary:P and S‐P arrival time data from 311 earthquakes and several thousand offshore and onshore shots have been used in simultaneous inversion for hypocenters, three‐dimensional (3‐D) Vp and Vp/Vs models in the Southern Alps region, New Zealand. The combined data result in a highly nonuniform ray path distribution, and linked nodes are used in sparsely sampled areas. Gravity data are used to improve the model below 20‐km depth, where it is poorly sampled by local earthquakes. The crustal Vp from 5 to 25 km depth is fairly uniform, generally ranging from 5.5 to 6.5 km/s, typical of graywacke and schist. Active fault zones tend to be correlated with low‐velocity zones. Where the Alpine fault is primarily strike slip, it is characterized by a vertical low‐velocity zone, to at least 15‐km depth. Where the fault is dipping and has a large dip‐slip component, it is characterized by a large region of low velocity above and southeast of the fault, to at least 14‐km depth, consistent with fluids and fracture density from active deformation. A large high‐velocity, high‐resistivity feature in the eastern Southern Alps may represent Mesozoic schist of higher metamorphic grade than its surroundings, which is relatively rigid and serves to both reduce deformation in the overlying basin and concentrate deformation in the adjoining low‐velocity region. The imaged crustal root is deepest 80‐km south of Mt. Cook and is asymmetric with a sharper gradient on the northwestern side. The approximate Moho shows regional variation, with 5–10 km thicker crust in Otago than Canterbury.
ISSN:0148-0227
2156-2202
DOI:10.1029/2001JB000567