This project is aimed at assessing damage to infrastructure and the potential for aftershocks immediately after destructive earthquakes such as the two that hit the region around Christchurch, New Zealand, during the past year. In this case, the close temporal association of the two events resulted in a case where we have more pre-seismic imagery from a wide range of satellite platforms before the second earthquake than is usual. We propose to use a combination of visual inspection and mapping of the images and automated cross-correlation (pixel-tracking) to characterize the coseismic and postseismic damage and deformation associated with each earthquake. We will also model the characteristics of each earthquake in order to assess the impact of stress changes on neighboring faults. Our primary goals are to 1) Quantify the evolving strain associated with the Darfield and Christchurch events, 2) Identify and map any observations of triggered slip on nearby faults, 3) Map liquefaction, landslides and detect incipient slumps along the Banks Peninsula and around Sumner and Lyttelton, and 4) Generate a slip distribution for both earthquakes that accounts for unknown aspects of the fault geometry and revise previous estimates of Coulomb stress change induced on neighboring faults.
The work in this proposal will help advance the field of image-based satellite geodesy, which has many demonstrated applications of interest to NSF, including earthquake science, glaciology, groundwater management, landslide forecasting and mitigation, etc. This particular sequence of two earthquakes occurring in close (but not immediate) temporal and spatial proximity is of great interest to researchers studying the modes of interaction between earthquakes on nearby faults. The use of satellite imagery to study earthquakes at the present time is limited in several ways ? coseismic and postseismic deformation studies rely on a small number of platforms and sensor types (e.g. SPOT imagery, SAR, LANDSAT), while other, often more high-resolution observation types are typically ingested into GIS software packages and inspected visually for signs of damage (e.g., building collapse, flooding, liquefaction). Our study may open up these data types for use in constraining the magnitude of deformation as well, which would speed up the potential response time for relief workers, and aid in the intelligent deployment of instruments that can monitor adjacent sections of fault that may be stressed by the initial earthquake.
This work involved the exploration of how satellite-based optical imagery can be used to rapidly characterize the deformation that occurs during an earthquake. We estimated horizontal ground displacements from imagery that was acquired by different satellites, with different pixel sizes and viewing orientations. Our work demonstrated the utility of such optical imagery analysis applied to data that does not necessarily have to have been obtained under optimal conditions - this opens up the option to use image pairs that bracket the event of interest more closely or that are acquired more rapidly after the event. We compare our results with those from satellite radar interferometry, and find that the ground displacements agree. Intellectual merit: Our work demonstrates the feasibility of ingesting data from disparate sensors into optical pixel-tracking algorithms. The sequence of earthquakes studied here (the 2010-2012 Canterbury sequence) is of interest because of the large size of the earthquake in a region that was not previously expected to experience large events, and the damaging aftershocks that occurred in the following months. We perform a statistical analysis of the expected static Coulomb stress changes for the sequence, an approach that can easily be applied to future events. Broader impacts: The Canterbury sequence caused extensive damage to the Christchurch, New Zealand, area. Much of the damage occurred during the aftershocks, which occured within the city of Christchurch itself. Rapidly-developed models of the characteristics of the original earthquake can improve our ability to forecast aftershocks and better coordinate relief efforts. Funds also supported data access used in the research of an early career female faculty member, two graduate students and a postdoc.
