%0 Journal Article %1 meng_etal:2012a %A Meng, L. %A Ampuero, J. P. %A Luo, Y. %A Wu, W. %A Ni, S. %D 2013 %J Earth, Planets and Space %K geophysics seismology %N 12 %P 1101--1109 %R 10.5047/eps.2012.05.010 %T Mitigating artifacts in back-projection source imaging with implications for frequency-dependent properties of the Tohoku-Oki earthquake %U http://dx.doi.org/10.5047/eps.2012.05.010 %V 64 %X Comparing teleseismic array back-projection source images of the 2011 Tohoku-Oki earthquake with results from static and kinematic finite source inversions has revealed little overlap between the regions of high- and low-frequency slip. Motivated by this interesting observation, back-projection studies extended to intermediate frequencies, down to about 0.1 Hz, have suggested that a progressive transition of rupture properties as a function of frequency is observable. Here, by adapting the concept of array response function to non-stationary signals, we demonstrate that the 'swimming artifact', a systematic drift resulting from signal non-stationarity, induces significant bias on beamforming back-projection at low frequencies. We introduce a 'reference window strategy' into the multitaper-MUSIC back-projection technique and significantly mitigate the 'swimming artifact' at high frequencies (1 s to 4 s). At lower frequencies, this modification yields notable, but significantly smaller, artifacts than time-domain stacking. We perform extensive synthetic tests that include a 3D regional velocity model for Japan. We analyze the recordings of the Tohoku-Oki earthquake at the USArray and at the European array at periods from 1 s to 16 s. The migration of the source location as a function of period, regardless of the back-projection methods, has characteristics that are consistent with the expected effect of the 'swimming artifact'. In particular, the apparent up-dip migration as a function of frequency obtained with the USArray can be explained by the 'swimming artifact'. This indicates that the most substantial frequency-dependence of the Tohoku-Oki earthquake source occurs at periods longer than 16 s. Thus, low-frequency back-projection needs to be further tested and validated in order to contribute to the characterization of frequency-dependent rupture properties.

@article{meng_etal:2012a, abstract = {Comparing teleseismic array back-projection source images of the 2011 Tohoku-Oki earthquake with results from static and kinematic finite source inversions has revealed little overlap between the regions of high- and low-frequency slip. Motivated by this interesting observation, back-projection studies extended to intermediate frequencies, down to about 0.1 Hz, have suggested that a progressive transition of rupture properties as a function of frequency is observable. Here, by adapting the concept of array response function to non-stationary signals, we demonstrate that the 'swimming artifact', a systematic drift resulting from signal non-stationarity, induces significant bias on beamforming back-projection at low frequencies. We introduce a 'reference window strategy' into the multitaper-MUSIC back-projection technique and significantly mitigate the 'swimming artifact' at high frequencies (1 s to 4 s). At lower frequencies, this modification yields notable, but significantly smaller, artifacts than time-domain stacking. We perform extensive synthetic tests that include a 3D regional velocity model for Japan. We analyze the recordings of the Tohoku-Oki earthquake at the USArray and at the European array at periods from 1 s to 16 s. The migration of the source location as a function of period, regardless of the back-projection methods, has characteristics that are consistent with the expected effect of the 'swimming artifact'. In particular, the apparent up-dip migration as a function of frequency obtained with the USArray can be explained by the 'swimming artifact'. This indicates that the most substantial frequency-dependence of the Tohoku-Oki earthquake source occurs at periods longer than 16 s. Thus, low-frequency back-projection needs to be further tested and validated in order to contribute to the characterization of frequency-dependent rupture properties.}, added-at = {2013-02-12T19:50:54.000+0100}, author = {Meng, L. and Ampuero, J. P. and Luo, Y. and Wu, W. and Ni, S.}, biburl = {https://www.bibsonomy.org/bibtex/2acc3ed07e0e4fa851deecc4c27daf5f6/nilsma}, day = 28, doi = {10.5047/eps.2012.05.010}, interhash = {835f6e126be21c239623651e65af25d7}, intrahash = {acc3ed07e0e4fa851deecc4c27daf5f6}, issn = {13438832}, journal = {Earth, Planets and Space}, keywords = {geophysics seismology}, month = jan, number = 12, pages = {1101--1109}, timestamp = {2021-02-09T13:26:37.000+0100}, title = {Mitigating artifacts in back-projection source imaging with implications for frequency-dependent properties of the Tohoku-Oki earthquake}, url = {http://dx.doi.org/10.5047/eps.2012.05.010}, volume = 64, year = 2013 }