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Relating teleseismic backprojection images to earthquake kinematics

Jiuxun Yin, & Marine A. Denolle

Published August 13, 2018, SCEC Contribution #8417, 2018 SCEC Annual Meeting Poster #083

Backprojection (BP) of teleseismic P waves is a powerful tool to study the evolution of seismic radiation of large earthquakes. The common interpretations on the BP results are qualitative comparisons with earthquake kinematic observations, such as the evolution of slip on the fault and rupture velocity. However, the direct relation between the BP images and physical properties of the earthquake rupture process remains unclear and is needed for further application of this technique. In this study, we start from a theoretical formulation of the BP images, which is linear in the frequency domain, and carry on a synthetic exercise with kinematic source representations and virtual receivers embedded in a homogeneous fullspace. We find that the fundamental linear formulation of the BP method is most correlated with the true kinematic source properties: the images from linear BP are a snapshot of the slip motion on the fault surface, after a spatial smoothing with a frequency-dependent resolution matrix F. We define a resolvability parameter for the resolution matrix F that quantifies the data resolution of the BP method. The direct comparison between the synthetic BP images and the kinematic models validates that the BP image can be directly used to track the spatio-temporal propagation of rupture front. However, because F is not strictly an identity matrix due to limited station coverage in space (azimuth and distance) and to the limited frequency bands of the seismograms, it remains difficult to recover the details in the rupture fronts from BP images. Since the resolution matrix F mostly depends on source mechanism and source-receiver geometry, we further calculate the resolvability and the corresponding resolvable source area/length for most tectonically active source regions and the commonly used seismic arrays. Based on this global resolvability analysis, we propose an empirical relation between the seismic frequency, resolvable area, and earthquake magnitude. It provides guidelines to properly choose the frequency band in seismic waveform and to interpret the BP image in terms of source slip rate. In general, this work attempts to provide a clear interpretation of the BP images in light of the real earthquake rupture process and give a systematic evaluation of seismic data limitations.

Yin, J., & Denolle, M. A. (2018, 08). Relating teleseismic backprojection images to earthquake kinematics. Poster Presentation at 2018 SCEC Annual Meeting.

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