Linking Geodetically Resolved Uplift to Long-Term Orogenic Exhumation in the Southern Alps, New Zealand

Abstract

A limitation in our understanding of the geodynamics of orogenies is the difficulty in resolving the spatial variations in long-term processes such as exhumation of the crust. Although geodesy can record ground motions to millimeter-scale precision at high spatial and temporal resolutions, these observations only cover a small fraction of the seismic cycle, and therefore may not represent the long-term behavior of an orogeny. Here, by considering various contributions to uplift over differing timescales, we attempt to constrain spatially resolved exhumation rates using observations of permanent interseismic uplift from InSAR, GPS, fault trenching and a range of modeling techniques. We apply our methodology to New Zealand's Southern Alps, an orogeny with known high exhumation rates and variable behavior along orogenic strike. We generate InSAR derived velocity fields which show uplift rates of up to 1 cm/yr focused around Aoraki/Mt Cook. Velocity field inversion shows that the structural make-up of the plate boundary exerts a major control on this spatial variability of exhumation due to a 15 (Formula presented.) shallowing of the Alpine Fault. Modeling the accumulated slip deficit indicates the Alpine Fault is capable of hosting great ((Formula presented.) (Formula presented.) 8) earthquakes. By combining the interseismic velocity fields and cosesimic displacement rates, we produce a map of the exhumation rates in the Southern Alps. These observations indicate a tectonic cause for a connection between long-term uplift and exhumation in this region. With careful consideration of other uplift contributions, our approach may be used in other orogenic belts.