Co-Registration of Optically Sensed Images and Correlation (COSI-Corr): an Operational Methodology for Ground Deformation Measurements

Recent methodological progress, Co-Registration of Optically Sensed Images and Correlation, outlined here, makes it possible to measure horizontal ground deformation from optical images on an operational basis, using the COSI-Corr software package. In particular, its sub-pixel capabilities allow for accurate mapping of surface ruptures and measurement of co-seismic offsets. We retrieved the fault rupture of the 2005 Mw 7.6 Kashmir earthquake from ASTER images, and we also present a dense mapping of the 1992 Mw 7.3 Landers earthquake of California, from the mosaicking of 30 pairs of aerial images

Influence of camera distortions on satellite image registration and change detection applications

Applications such as change detection and digital elevation model extraction from optical images require a rigorous modeling of the acquisition geometry. We show that the unrecorded satellite jitter during image acquisition, and the uncertainties on the CCD arrays geometry are the current major limiting factors for applications requiring high accuracy. These artifacts are identified and quantified on several optical satellites, i.e., SPOT, ASTER, QuickBird, and HiRISE

Deformation during the 1975–1984 Krafla rifting crisis, NE Iceland, measured from historical optical imagery

We measure the displacement field resulting from the 1975–1984 Krafla rifting crisis, NE Iceland, using optical image correlation. Images are processed using the COSI-Corr software package. Surface extension is accommodated on normal faults and fissures which bound the rift zone, in response to dike injection at depth. Correlation of declassified KH-9 spy and SPOT5 satellite images reveals extension between 1977–2002 (2.5 m average opening over 80 km), while correlation of aerial photos between 1957–1990 provide measurements of the total extension (average 4.3 m opening over 80 km). Our results show ∼8 m of opening immediately north of Krafla caldera, decreasing to 3–4 m at the northern end of the rift. Correlation of aerial photos from 1957–1976 reveal a bi-modal pattern of opening along the rift during the early crisis, which may indicate either two different magma sources located at either end of the rift zone (a similar pattern of opening was observed in the 2005 Afar rift crisis in East Africa), or variations in rock strength along the rift. Our results provide new information on how past dike injection events accommodate long-term plate spreading, as well as providing more details on the Krafla rift crisis. This study also highlights the potential of optical image correlation using inexpensive declassified spy satellite and aerial photos to measure deformation of the Earth's surface going back many decades, thus providing a new tool for measuring Earth surface dynamics, e.g. glaciers, landsliding, coastal erosion, volcano monitoring and earthquake studies, when InSAR and GPS data are not available

Revisiting Past Earthquakes and Seismo-Volcanic Crises Using Declassified Optical Satellite Imagery

Recent development of the user-friendly software package “Co-registration of Optically Sensed Images and Correlation” (COSI-Corr), which allows for automatic and precise ortho-rectification, co-registration, and sub-pixel correlation of pushbroom satellite and aerial images, has enabled Earth’s surface dynamics to be accurately monitored using optical imagery [1]. This technique compares two images of the Earth’s surface that were acquired at different times, and estimates any potential pixel shifts between them with an accuracy typically better than 1/10 of the pixel size. Correlation of both satellite and aerial images has been successfully used to identify coseismic ground ruptures and quantify fault offsets during large earthquakes [2]–[4], as well as monitoring sand dune migration, landsliding, ice flow [5] [6], and volcanic activity [7] [8]. In this study, we demonstrate that recently declassified US spy satellite images can be used to measure ground deformation resulting from seismotectonic and volcanic events using optical sub-pixel correlation. KH-9 Hexagon satellite images, with a swath size of 250×125 km, were acquired by the US government between 1971 and 1980, and are available for purchase from the United States Geological Survey (USGS) at small cost ($30 per image). During this period, around 29,000 images were acquired globally [9], providing a comprehensive record of the Earth’s surface at 6–9m resolution

Revisiting Past Earthquakes and Seismo-Volcanic Crises Using Declassified Optical Satellite Imagery

Recent development of the user-friendly software package “Co-registration of Optically Sensed Images and Correlation” (COSI-Corr), which allows for automatic and precise ortho-rectification, co-registration, and sub-pixel correlation of pushbroom satellite and aerial images, has enabled Earth’s surface dynamics to be accurately monitored using optical imagery [1]. This technique compares two images of the Earth’s surface that were acquired at different times, and estimates any potential pixel shifts between them with an accuracy typically better than 1/10 of the pixel size. Correlation of both satellite and aerial images has been successfully used to identify coseismic ground ruptures and quantify fault offsets during large earthquakes [2]–[4], as well as monitoring sand dune migration, landsliding, ice flow [5] [6], and volcanic activity [7] [8]. In this study, we demonstrate that recently declassified US spy satellite images can be used to measure ground deformation resulting from seismotectonic and volcanic events using optical sub-pixel correlation. KH-9 Hexagon satellite images, with a swath size of 250×125 km, were acquired by the US government between 1971 and 1980, and are available for purchase from the United States Geological Survey (USGS) at small cost ($30 per image). During this period, around 29,000 images were acquired globally [9], providing a comprehensive record of the Earth’s surface at 6–9m resolution

Nonlinear seismic analysis of reinforced concrete structures using POD reduced order method

This paper presents an extension of the Proper Orthogonal Decomposition method (POD) to nonlinear dynamic analysis of reinforced concrete multistory frame structure where the material nonlinearity is modeled by the multi-fiber section. To test the effectiveness of this approach, we first perform a nonlinear dynamic analysis under a seismic excitation using a direct implicit time integration scheme. Then, based on structural response observations, POD modes were extracted and used to reduce the structural system subjected to different earthquakes. A comparison was made between full model and reduced model analysis in order to assess the effectiveness of this technique

Quantifying near-field and off-fault deformation patterns of the 1992 M_w 7.3 Landers earthquake

Coseismic surface deformation in large earthquakes is typically measured using field mapping and with a range of geodetic methods (e.g., InSAR, lidar differencing, and GPS). Current methods, however, either fail to capture patterns of near-field coseismic surface deformation or lack preevent data. Consequently, the characteristics of off-fault deformation and the parameters that control it remain poorly understood. We develop a standardized method to fully measure the surface, near-field, coseismic deformation patterns at high resolution using the COSI-Corr program by correlating pairs of aerial photographs taken before and after the 1992 M_w 7.3 Landers earthquake. COSI-Corr offers the advantage of measuring displacement across the entire zone of surface deformation and over a wider aperture than that available to field geologists. For the Landers earthquake, our measured displacements are systematically larger than the field measurements, indicating the presence of off-fault deformation. We show that 46% of the total surface displacement occurred as off-fault deformation, over a mean deformation width of 154 m. The magnitude and width of off-fault deformation along the rupture is primarily controlled by the macroscopic structural complexity of the fault system, with a weak correlation with the type of near-surface materials through which the rupture propagated. Both the magnitude and width of distributed deformation are largest in stepovers, bends, and at the southern termination of the surface rupture. We find that slip along the surface rupture exhibits a consistent degree of variability at all observable length scales and that the slip distribution is self-affine fractal with dimension of 1.56

New constraints on dike injection and fault slip during the 1975–1984 Krafla rift crisis, NE Iceland

Correlation of KH9 spy and SPOT5 satellite images, airphotos, digital elevation model differencing, electronic distance measurement, and leveling survey data is used to constrain the deformation resulting from the 1975–1984 Krafla rifting crisis. We find that diking typically extends to depths of 5 km, while the dike tops range from 0 km in the caldera region to 3 km at the northern end of the rift. Extension is accommodated by diking at depth and normal faulting in the shallowest crust. In the southern section of the Krafla rift, surface opening is 80% of the dike opening at depth. Over the 70–80 km length of the rift, the average dike opening was 4.3–5.4 m. From these estimates, we calculate the total geodetic moment released over the Krafla rift crisis, 4.4–9.0×10^(19) Nm, which is an order of magnitude higher than the seismic moment released over the same time period, ~5.8×10^(18) Nm. The total volume of magma added to the upper crust was 1.1–2.1×10^9m^3. This study highlights how optical image correlation using inexpensive declassified spy satellite and airphotos, combined with simple models of crustal deformation, can provide important constraints on the deformation resulting from past earthquake and volcanic events

Refining the shallow slip deficit

Geodetic slip inversions for three major (M_w > 7) strike-slip earthquakes (1992 Landers, 1999 Hector Mine and 2010 El Mayor–Cucapah) show a 15–60 per cent reduction in slip near the surface (depth < 2 km) relative to the slip at deeper depths (4–6 km). This significant difference between surface coseismic slip and slip at depth has been termed the shallow slip deficit (SSD). The large magnitude of this deficit has been an enigma since it cannot be explained by shallow creep during the interseismic period or by triggered slip from nearby earthquakes. One potential explanation for the SSD is that the previous geodetic inversions lack data coverage close to surface rupture such that the shallow portions of the slip models are poorly resolved and generally underestimated. In this study, we improve the static coseismic slip inversion for these three earthquakes, especially at shallow depths, by: (1) including data capturing the near-fault deformation from optical imagery and SAR azimuth offsets; (2) refining the interferometric synthetic aperture radar processing with non-boxcar phase filtering, model-dependent range corrections, more complete phase unwrapping by SNAPHU (Statistical Non-linear Approach for Phase Unwrapping) assuming a maximum discontinuity and an on-fault correlation mask; (3) using more detailed, geologically constrained fault geometries and (4) incorporating additional campaign global positioning system (GPS) data. The refined slip models result in much smaller SSDs of 3–19 per cent. We suspect that the remaining minor SSD for these earthquakes likely reflects a combination of our elastic model's inability to fully account for near-surface deformation, which will render our estimates of shallow slip minima, and potentially small amounts of interseismic fault creep or triggered slip, which could ‘make up’ a small percentages of the coseismic SSD during the interseismic period. Our results indicate that it is imperative that slip inversions include accurate measurements of near-fault surface deformation to reliably constrain spatial patterns of slip during major strike-slip earthquakes