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3D coseismic surface displacements from historical aerial photographs of the 1987 Edgecumbe earthquake, New Zealand
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  • Jaime Elizabeth Delano,
  • Timothy Stahl,
  • Andrew Howell,
  • Kate Clark
Jaime Elizabeth Delano
Univeristy of Canterbury

Corresponding Author:jaimedelano@gmail.com

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Timothy Stahl
Univeristy of Canterbury
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Andrew Howell
University of Canterbury
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Kate Clark
GNS Science
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Earthquake surface deformation provides key constraints on the geometry, kinematics, displacements, and complexity of fault rupture. However, deriving these precise characteristics from past earthquakes is complicated by a lack of detailed knowledge of landforms before the earthquake and how the landform has since been modified. The 1987 Mw 6.6 Edgecumbe earthquake in the northern Taupō volcanic zone in New Zealand represents a moderate-magnitude earthquake with complicated surface rupture that occurred before widespread high-resolution topographic data were available. We use historical aerial photos to build pre- and post-earthquake digital surface models using structure-from-motion techniques. By differencing the two surface models, we more definitively measure discrete and distributed deformation from this earthquake and compare the effectiveness of the technique to traditional field- and lidar-based studies. We identified most fault traces recognized by field mapping in 1987, mapped new traces not recorded in the field, and take denser, detailed remote slip measurements with a vertical separation resolution of ~0.3 m. Our maximum and average vertical separation measurements on the Edgecumbe fault trace (2.5 ± 0.3 m and 1.2 m, respectively), are similar to field-based maximum and recalculated averages of 2.4 m and 1.1 m, respectively. Importantly, this technique is able to discern between new fault scarps and pre-existing fault scarps better than field techniques or lidar-based measurements alone. Results from this approach can be used to refine estimated subsurface fault geometries and slip distributions at depth, and here is used to investigate potential magmatic-tectonic stress trigging in the northern Taupō volcanic zone.