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Poster #106, Tectonic Geodesy

Using optical image correlation to quantify the three-dimensional displacement field of historical events: Example from the 1959 Mw 7.2 Hebgen Lake earthquake.

Lucia Andreuttiova, James Hollingsworth, Pieter Vermeesch, Thomas M. Mitchell, & Eric Bergman
Poster Image: 

Poster Presentation

2021 SCEC Annual Meeting, Poster #106, SCEC Contribution #11479 VIEW PDF
Optical image correlation has been previously used to retrieve the ground displacement caused by recent earthquakes. However, applying this method to historical ruptures can be challenging because historical aerial photographs may be affected by film degradation/warping, unknown camera parameters, small ground footprints, and limited and/or variable stereo overlap. These limitations hinder the precise co-registration and orthorectification of images, resulting in corrupted displacement estimates. To address this problem we present a workflow that automatically co-registers, orthorectifies and correlates large numbers of historical images. The method utilises image correlation and structure-f...rom-motion (SfM) techniques allowing the reconstruction of an internally consistent high-resolution DEM and orthorectified image mosaics, which are then used to calculate the horizontal and vertical components of the surface offset.

The Mw 7.2 1959 Hebgen Lake earthquake was one of the 20th century’s largest dip-slip continental earthquakes. It was covered by several sets of high-resolution aerial images, which makes it an ideal site to retrieve three-dimensional offset measurements. The results presented here capture approximately 380 km2 of the fault zone and reveal the EW, NS and vertical components of the near-field and far-field displacement. Our data are systematically higher in comparison to existing studies and field observations. It is possible that this discrepancy reflects an off-fault deformation distributed in the rock volume surrounding the main rupture. Additionally, the surface displacement field retrieved through image correlation reveals two previously unmapped strike-slip surface ruptures, which are inconsistent with the NE-SW directed extension but correlate with aftershocks that occurred two hours after the main event. These ruptures likely accommodate internal deformation related to the changing geometry of the mainshock rupture. This study not only presents new techniques to study historical earthquakes from aerial imagery but also sheds a light on the complex kinematics and geological history of the Hegen Lake rupture as one of a few normal faults events ever studied by the optical image correlation.