Using Kinematic models to Evaluate the Back Projection Results

Baoning Wu, Bo Li, David D. Oglesby, & Abhijit Ghosh

Published August 14, 2018, SCEC Contribution #8523, 2018 SCEC Annual Meeting Poster #085

Back projection is a useful method for imaging the rupture process of large earthquakes. Despite great success in practice, there are still many questions on how to correctly interpret back projection results. First, the fundamental result of back-projection is the amplitude and location of maximum high-frequency seismic radiation; however, the seismic energy radiation mechanism is complicated for a large earthquake. The seismic energy received by a teleseismic station is generated not only from slip acceleration and deceleration, but also from rupture front acceleration and deceleration (Madariaga, 1977). Therefore, the physical meaning behind the beam energy and the location of maximum beam energy remain enigmatic. In addition, rupture can propagate on multiple locations on a fault system, including different segments simultaneously during a large earthquake, while the back projection method can only pick one location of maximum beam energy. How the back projection method works under this situation is still unclear. In this study, we generate synthetic earthquakes with kinematic model, and calculate the corresponding far field ground motion with the propagator matrix method. The back projection method will be performed using the synthetic seismograms, and the results will be compared with the known rupture history. Such comparisons using multiple models and their back projection results using multiple arrays demonstrate some similar characteristics. First, the back projection results show generally slower rupture velocity than the dynamic models. Second, depending on the rupture directions and array locations, the arrays on different azimuths can show different rupture propagations, especially when the events rupture in different directions or have branch ruptures. Third, rupture velocity changes will result in a higher amplitude in the seismograms, which will lead to stronger beam power in the back projection results. More dynamic and kinematic models will be designed to help us better understand the physical meaning of the back projection results and better interpret the back projection results.

Key Words
Back projection, synthetic test, kinematic model

Citation
Wu, B., Li, B., Oglesby, D. D., & Ghosh, A. (2018, 08). Using Kinematic models to Evaluate the Back Projection Results. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology