E. Nissen - Profile on Academia.edu (original) (raw)

Papers by E. Nissen

3-D earthquake surface displacements from differencing pre-and post-event LiDAR point clouds

Rapid mapping of ultrafine fault zone topography with structure from motion

ABSTRACT Structure from Motion (SfM) generates high-resolution topography and coregistered textur... more ABSTRACT Structure from Motion (SfM) generates high-resolution topography and coregistered texture (color) from an unstructured set of overlapping photographs taken from vary- ing viewpoints, overcoming many of the cost, time, and logistical limitations of Light Detection and Ranging (LiDAR) and other topographic surveying methods. This paper provides the first investigation of SfM as a tool for mapping fault zone topography in areas of sparse or low-lying vegetation. First, we present a simple, affordable SfM workflow, based on an unmanned helium balloon or motorized glider, an inexpensive camera, and semiautomated software. Second, we illustrate the system at two sites on southern California faults covered by exist- ing airborne or terrestrial LiDAR, enabling a comparative assessment of SfM topography resolution and precision. At the first site, an ~0.1 km2 alluvial fan on the San Andreas fault, a colored point cloud of density mostly >700 points/m2 and a 3 cm digital elevation model (DEM) and orthophoto were produced from 233 photos collected ~50 m above ground level. When a few global positioning system ground control points are incorporated, closest point vertical distances to the much sparser (~4 points/m2) airborne LiDAR point cloud are mostly <3 cm. The second site spans an ~1 km section of the 1992 Landers earthquake scarp. A colored point cloud of density mostly >530 points/m2 and a 2 cm DEM and orthophoto were produced from 450 photos taken from ~60 m above ground level. Closest point vertical distances to exist- ing terrestrial LiDAR data of comparable density are mostly <6 cm. Each SfM survey took ~2 h to complete and several hours to generate the scene topography and texture. SfM greatly facilitates the imaging of subtle geomorphic offsets related to past earth- quakes as well as rapid response mapping or long-term monitoring of faulted landscapes.

Characterisation of active faulting and earthquake hazard in the Mongolian Altay Mountains based on previously unknown ancient earthquake surface ruptures

Geophysical Journal International, 2007

M w 7.2 Siberian Altai earthquake was the largest to have struck the Altai mountains in more than... more M w 7.2 Siberian Altai earthquake was the largest to have struck the Altai mountains in more than seventy years, and was closely followed by two M w 6.2 and 6.6 aftershocks. We use radar interferometry, seismic bodywaves and field investigations to examine the source processes of these earthquakes. The main shock of the initial earthquake ruptured a subvertical, ∼NW-SE striking dextral strike-slip fault. The fault was previously unrecognised; although it approximately follows the southwestern boundaries of two intermontane depressions within the interior northwestern Altai, it has very little topographic expression. A ∼NE-dipping M w ∼ 6.7 reverse subevent, possibly triggered by shear waves from the main shock, occurred ten seconds afterwards strike to the southeast. The later M w 6.2 and 6.6 aftershocks were dextral strike-slip events which contributed further to deformation in the northwest part of the fault zone. However, interferometric and bodywave models disagree significantly on the source parameters of the earthquakes, in particular the total moment released and the dip of the fault planes. Trade-offs of fault dip with moment and centroid depth in the bodywave modelling can account for some, but not all, of these discrepancies. The interferometric data is unevenly distributed, containing many more data points on one side of the fault zone than the other; however, on the basis of calculations with synthetic data we rule this out as a reason for the discrepancies in fault parameters. The lower moment predicted by interferometry could be explained by the lack of coherent data close to the faulting, if slip was concentrated at very shallow depths. The dip yielded by the interferometric modelling might be influenced by lateral changes in elastic properties, although these would also affect the bodywave solutions. The earthquake sequence occurred close to recent palaeomagnetic measurements of late Cenozoic anticlockwise rotations. These suggest that the right-lateral strike-slip faulting that ruptured in the 2003 earthquakes accommodates regional ∼NNE-SSW shortening by rotating anticlockwise over time. The reverse subevent is a rare case of pure shortening perpendicular to the trend of the Altai range.

A reassessment of earthquake depths in the Zagros with observations from InSAR and local seismic data

Abstract The Zagros mountains of Iran are one of the most seismically active fold-and-thrust belt... more Abstract The Zagros mountains of Iran are one of the most seismically active fold-and-thrust belts in the world, with frequent reverse faulting earthquakes of Mw 5-6 and rare larger events of up to Mw~ 6.7. Earthquakes in the Zagros rarely rupture the surface, and there is ...

We use two recent Japanese earthquakes to demonstrate the rich potential, as well as some of the ... more We use two recent Japanese earthquakes to demonstrate the rich potential, as well as some of the challenges, of differencing repeat airborne Light Detection and Ranging (lidar) topographic data to measure coseismic fault zone deformation. We focus on densely-vegetated sections of the 14 June 2008 Iwate–Miyagi (Mw 6.9) and 11 April 2011 Fukushima–Hamadori (Mw 7.1) earthquake ruptures, each covered by 2 m-resolution pre-event and 1 m-resolution post-event bare Earth digital terrain models (DTMs) obtained from commercial lidar providers. Three-dimensional displacements and rotations were extracted from these datasets using an adaptation of the Iterative Closest Point (ICP) algorithm. These displacements remain coherent close to surface fault breaks, as well as within dense forest, despite intervals of ∼2 years (Iwate–Miyagi) and ∼4 years (Fukushima–Hamadori) encompassed by the lidar scenes. Differential lidar analysis is thus complementary to Interferometric Synthetic Aperture Radar (InSAR) and sub-pixel correlation techniques which often break down under conditions of long time intervals, dense vegetation or steep displacement gradients. Although the ICP displacements are much noisier than overlapping InSAR line-of-sight displacements, they still provide powerful constraints on near-surface fault slip. In the Fukushima–Hamadori case, near-fault displacements and rotations are consistent with decreased primary fault slip at very shallow depths of a few tens of meters, helping to account for the large, along-strike heterogeneity in surface offsets observed in the field. This displacement field also captures long-wavelength deformation resulting from the 11 March 2011 Tohoku great earthquake.

3-D earthquake surface displacements from differencing pre-and post-event LiDAR point clouds

Rapid mapping of ultrafine fault zone topography with structure from motion

ABSTRACT Structure from Motion (SfM) generates high-resolution topography and coregistered textur... more ABSTRACT Structure from Motion (SfM) generates high-resolution topography and coregistered texture (color) from an unstructured set of overlapping photographs taken from vary- ing viewpoints, overcoming many of the cost, time, and logistical limitations of Light Detection and Ranging (LiDAR) and other topographic surveying methods. This paper provides the first investigation of SfM as a tool for mapping fault zone topography in areas of sparse or low-lying vegetation. First, we present a simple, affordable SfM workflow, based on an unmanned helium balloon or motorized glider, an inexpensive camera, and semiautomated software. Second, we illustrate the system at two sites on southern California faults covered by exist- ing airborne or terrestrial LiDAR, enabling a comparative assessment of SfM topography resolution and precision. At the first site, an ~0.1 km2 alluvial fan on the San Andreas fault, a colored point cloud of density mostly >700 points/m2 and a 3 cm digital elevation model (DEM) and orthophoto were produced from 233 photos collected ~50 m above ground level. When a few global positioning system ground control points are incorporated, closest point vertical distances to the much sparser (~4 points/m2) airborne LiDAR point cloud are mostly <3 cm. The second site spans an ~1 km section of the 1992 Landers earthquake scarp. A colored point cloud of density mostly >530 points/m2 and a 2 cm DEM and orthophoto were produced from 450 photos taken from ~60 m above ground level. Closest point vertical distances to exist- ing terrestrial LiDAR data of comparable density are mostly <6 cm. Each SfM survey took ~2 h to complete and several hours to generate the scene topography and texture. SfM greatly facilitates the imaging of subtle geomorphic offsets related to past earth- quakes as well as rapid response mapping or long-term monitoring of faulted landscapes.

Characterisation of active faulting and earthquake hazard in the Mongolian Altay Mountains based on previously unknown ancient earthquake surface ruptures

Geophysical Journal International, 2007

M w 7.2 Siberian Altai earthquake was the largest to have struck the Altai mountains in more than... more M w 7.2 Siberian Altai earthquake was the largest to have struck the Altai mountains in more than seventy years, and was closely followed by two M w 6.2 and 6.6 aftershocks. We use radar interferometry, seismic bodywaves and field investigations to examine the source processes of these earthquakes. The main shock of the initial earthquake ruptured a subvertical, ∼NW-SE striking dextral strike-slip fault. The fault was previously unrecognised; although it approximately follows the southwestern boundaries of two intermontane depressions within the interior northwestern Altai, it has very little topographic expression. A ∼NE-dipping M w ∼ 6.7 reverse subevent, possibly triggered by shear waves from the main shock, occurred ten seconds afterwards strike to the southeast. The later M w 6.2 and 6.6 aftershocks were dextral strike-slip events which contributed further to deformation in the northwest part of the fault zone. However, interferometric and bodywave models disagree significantly on the source parameters of the earthquakes, in particular the total moment released and the dip of the fault planes. Trade-offs of fault dip with moment and centroid depth in the bodywave modelling can account for some, but not all, of these discrepancies. The interferometric data is unevenly distributed, containing many more data points on one side of the fault zone than the other; however, on the basis of calculations with synthetic data we rule this out as a reason for the discrepancies in fault parameters. The lower moment predicted by interferometry could be explained by the lack of coherent data close to the faulting, if slip was concentrated at very shallow depths. The dip yielded by the interferometric modelling might be influenced by lateral changes in elastic properties, although these would also affect the bodywave solutions. The earthquake sequence occurred close to recent palaeomagnetic measurements of late Cenozoic anticlockwise rotations. These suggest that the right-lateral strike-slip faulting that ruptured in the 2003 earthquakes accommodates regional ∼NNE-SSW shortening by rotating anticlockwise over time. The reverse subevent is a rare case of pure shortening perpendicular to the trend of the Altai range.

A reassessment of earthquake depths in the Zagros with observations from InSAR and local seismic data

Abstract The Zagros mountains of Iran are one of the most seismically active fold-and-thrust belt... more Abstract The Zagros mountains of Iran are one of the most seismically active fold-and-thrust belts in the world, with frequent reverse faulting earthquakes of Mw 5-6 and rare larger events of up to Mw~ 6.7. Earthquakes in the Zagros rarely rupture the surface, and there is ...

We use two recent Japanese earthquakes to demonstrate the rich potential, as well as some of the ... more We use two recent Japanese earthquakes to demonstrate the rich potential, as well as some of the challenges, of differencing repeat airborne Light Detection and Ranging (lidar) topographic data to measure coseismic fault zone deformation. We focus on densely-vegetated sections of the 14 June 2008 Iwate–Miyagi (Mw 6.9) and 11 April 2011 Fukushima–Hamadori (Mw 7.1) earthquake ruptures, each covered by 2 m-resolution pre-event and 1 m-resolution post-event bare Earth digital terrain models (DTMs) obtained from commercial lidar providers. Three-dimensional displacements and rotations were extracted from these datasets using an adaptation of the Iterative Closest Point (ICP) algorithm. These displacements remain coherent close to surface fault breaks, as well as within dense forest, despite intervals of ∼2 years (Iwate–Miyagi) and ∼4 years (Fukushima–Hamadori) encompassed by the lidar scenes. Differential lidar analysis is thus complementary to Interferometric Synthetic Aperture Radar (InSAR) and sub-pixel correlation techniques which often break down under conditions of long time intervals, dense vegetation or steep displacement gradients. Although the ICP displacements are much noisier than overlapping InSAR line-of-sight displacements, they still provide powerful constraints on near-surface fault slip. In the Fukushima–Hamadori case, near-fault displacements and rotations are consistent with decreased primary fault slip at very shallow depths of a few tens of meters, helping to account for the large, along-strike heterogeneity in surface offsets observed in the field. This displacement field also captures long-wavelength deformation resulting from the 11 March 2011 Tohoku great earthquake.