Co-seismic vertical displacements from a single post-seismic lidar DEM: example from the 2010 El Mayor-Cucapah earthquake

A method is outlined by means of which it is possible to estimate high-resolution vertical displacements due to an earthquake even in the case where high-resolution topography is lacking before the earthquake. This result can be achieved by combining a highly accurate, post-event digital elevation model (DEM), for example lidar, with archived satellite imagery. The method is illustrated by calculating vertical displacements for the 2010 El Mayor-Cucapah earthquake. For this earthquake, there are both pre- and post-event lidar DEMs from which vertical displacements may also be estimated after correcting for the lateral advection of topography due to horizontal displacements. A comparison between the two means of deriving vertical displacements shows generally good agreement, with the displacements obtained using satellite imagery performing better in high relief areas. As a result of this property, we are able to trace the vertical offsets due to the El Mayor-Cucapah earthquake as the rupture jumped from the Pescadores fault to the Borrego fault in propagating through the high relief of the Sierra Cucapah

Assessing the ability of Pleiades stereo imagery to determine height changes in earthquakes: a case study for the El Mayor-Cucapah epicentral area

High-resolution surface topography is valuable for studying coseismic fault zone deformation and fault geometry. It enables us to measure three-dimensional surface displacements in earthquakes, as shown in recent studies that used light detection and ranging (LiDAR) to determine coseismic motion. However, the applicability of LiDAR is limited by its relatively high cost and low availability. In this study, we use the 2010 El Mayor-Cucapah earthquake to demonstrate the capability of Pleiades stereo imagery to measure coseismic vertical ground displacement. We acquired post-earthquake Pleiades tri-stereo imagery from backward, near-nadir and forward orientations for a 45 km × 7 km portion of the epicentral area. 1-m resolution digital elevation models (DEMs) were produced with the four different combinations of incidence angles and compared to the post-earthquake LiDAR DEM. Elevations from tri-stereo have slightly (∼15%) smaller uncertainties than bi-stereo as the tri-stereo DEM incorporates more observations. Elevation differences between the Pleiades and post-earthquake LiDAR DEMs show that the vertical accuracy of the Pleiades DEMs is ∼0.3 m. By differencing the Pleiades DEM and the pre-earthquake, 5-m resolution LiDAR DEM, we mapped metre and sub-metre offsets along the faults obtaining results comparable to a previous study that differenced the two LiDAR DEMs. This is the first case study of assessing very high-resolution (VHR) satellite stereo imagery to determine sub-metre vertical ground displacement in an earthquake. By extension, we expect it to be possible to measure sub-metre vertical offsets occurring in earthquakes using pre- and post-earthquake VHR stereo imagery

Geophysical constraints on the dynamics of spreading centres from rifting episodes on land

Most of the Earth's crust is created along 60,000 km of mid-ocean ridge system. Here, tectonic plates spread apart and, in doing so, gradually build up stress. This stress is released during rifting episodes, when bursts of magmatic activity lead to the injection of vertical sheets of magma — termed dykes — into the crust. Only 2% of the global mid-ocean ridge system is above sea level, so making direct observations of the rifting process is difficult. However, geodetic and seismic observations exist from spreading centres in Afar (East Africa) and Iceland that are exposed at the land surface. Rifting episodes are rare, but the few that have been well observed at these sites have operated with remarkably similar mechanisms. Specifically, magma is supplied to the crust in an intermittent manner, and is stored at multiple positions and depths. It then laterally intrudes in dykes within the brittle upper crust. Depending on the availability of magma, multiple magma centres can interact during one rifting episode. If we are to forecast large eruptions at spreading centres, rifting-cycle models will need to fully incorporate realistic crust and mantle properties, as well as the dynamic transport of magma