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.
%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
}