Joint Modeling of Fault Related Fold Kinematics and Marine Terrace Uplift to Estimate Active Fault Slip Rates in North Canterbury, New Zealand
Abstract
The often-blind thrust faults that underlie fault-propagation folds pose a seismic hazard that is difficult to quantify. Fold kinematic models provide a means to infer fault structure and slip rates, but they are nonunique and subject to uncertainties in the choice and parameters of any given model. Geomorphic markers of deformation provide not only a way to measure deformation rates but also an additional constraint on the model itself, as they respond to the same patterns of uplift and deformation that determine the fold geometry. Here we model fault-propagation folds in the North Canterbury fold and thrust belt on the South Island of New Zealand, where dated Quaternary marine terraces uplifted on the limbs of fault-propagation folds serve as markers of deformation. A Markov chain Monte Carlo algorithm is used to test fold kinematic models by cross section restoration. Terrace strath geometry is integrated into this model and restored along with the geologic structure in order to identify models that produce an initially near-horizontal terrace at the appropriate paleo-sea level. This joint inversion of geologic and geomorphic data narrows the range of possible models compared to the geologic data alone, and the model results provide estimates of fault slip rates and their uncertainties. Two possible models of fault geometry are considered: 1. a fault composed of two planar, dipping segments and, 2. an elliptically-shaped listric fault with a horizontal detachment. The two geometries predict similar fault slip rates near the surface but differ at greater depth, and aspects of the deep fault geometry such as detachment depth remain difficult to constrain. Fault slip rates along the coast are mostly about 1 mm/yr but range as high as 4 mm/yr and vary substantially over time on one of the structures studied. Fault slip rates offshore, as determined from folded growth strata, are <1 mm/yr and mostly about 0.2 mm/yr. Fold ages estimated from slip rates are similar for both onshore and offshore regions, and a similar listric fault model can explain folding in both regions. While some uncertainty remains in fault geometry and slip rates, joint modeling of geologic and geomorphic (marine terrace) data allows us to quantify this uncertainty and to narrow the range of possible models compared to those that fit the geologic data alone.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP54A..05O
- Keywords:
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- 1105 Quaternary geochronology;
- GEOCHRONOLOGYDE: 1130 Geomorphological geochronology;
- GEOCHRONOLOGYDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICSDE: 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS