scholarly journals Tomography of Southern California Via Bayesian Joint Inversion of Rayleigh Wave Ellipticity and Phase Velocity From Ambient Noise Cross-Correlations

2018 ◽  
Vol 123 (11) ◽  
pp. 9933-9949 ◽  
Author(s):  
E. M. Berg ◽  
F.-C. Lin ◽  
A. Allam ◽  
H. Qiu ◽  
W. Shen ◽  
...  
Keyword(s):  
Phase Velocity ◽  
Rayleigh Wave ◽  
Ambient Noise ◽  
Southern California ◽  
Joint Inversion ◽  
Cross Correlations

scholarly journals On seismic ambient noise cross-correlation and surface-wave attenuation

2019 ◽  
Vol 219 (3) ◽  
pp. 1568-1589
Author(s):  
Lapo Boschi ◽  
Fabrizio Magrini ◽  
Fabio Cammarano ◽  
Mark van der Meijde
Keyword(s):  
Rayleigh Wave ◽  
Ambient Noise ◽  
Cross Correlation ◽  
Wave Attenuation ◽  
Mathematical Expression ◽  
Seismic Ambient Noise ◽  
Multiplicative Factor ◽  
Cross Correlations ◽  
Noise Cross Correlation ◽  
Preliminary Application

SUMMARY We derive a theoretical relationship between the cross correlation of ambient Rayleigh waves (seismic ambient noise) and the attenuation parameter α associated with Rayleigh-wave propagation. In particular, we derive a mathematical expression for the multiplicative factor relating normalized cross correlation to the Rayleigh-wave Green’s function. Based on this expression, we formulate an inverse problem to determine α from cross correlations of recorded ambient signal. We conduct a preliminary application of our algorithm to a relatively small instrument array, conveniently deployed on an island. In our setup, the mentioned multiplicative factor has values of about 2.5–3, which, if neglected, could result in a significant underestimate of α. We find that our inferred values of α are reasonable, in comparison with independently obtained estimates found in the literature. Allowing α to vary with respect to frequency results in a reduction of misfit between observed and predicted cross correlations.

scholarly journals Crust and upper mantle structures of the Makran subduction zone in south-east Iran by seismic ambient noise tomography

2014 ◽  
Vol 6 (1) ◽  
pp. 1-34 ◽  
Author(s):  
M. Abdetedal ◽  
Z. H. Shomali ◽  
M. R. Gheitanchi
Keyword(s):  
Surface Wave ◽  
Rayleigh Wave ◽  
Group Velocity ◽  
Ambient Noise ◽  
Surface Wave Tomography ◽  
Seismic Ambient Noise ◽  
Velocity Anomaly ◽  
Empirical Green’S Functions ◽  
Wave Tomography ◽  
Cross Correlations

Abstract. We applied seismic ambient noise surface wave tomography to estimate Rayleigh wave empirical Green's functions from cross-correlations to study crust and uppermost mantle structure beneath the Makran region in south-east Iran. We analysed 12 months of continuous data from January 2009 through January 2010 recorded at broadband seismic stations. We obtained group velocity of the fundamental mode Rayleigh-wave dispersion curves from empirical Green's functions between 10 and 50 s periods by multiple-filter analysis and inverted for Rayleigh wave group velocity maps. The final results demonstrate significant agreement with known geological and tectonic features. Our tomography maps display low-velocity anomaly with south-western north-eastern trend, comparable with volcanic arc settings of the Makran region, which may be attributable to the geometry of Arabian Plate subducting overriding lithosphere of the Lut block. At short periods (<20 s) there is a pattern of low to high velocity anomaly in northern Makran beneath the Sistan Suture Zone. These results are evidence that surface wave tomography based on cross correlations of long time-series of ambient noise yields higher resolution group speed maps in those area with low level of seismicity or those region with few documented large or moderate earthquake, compare to surface wave tomography based on traditional earthquake-based measurements.

Shear-wave structure of southern Sweden from precise phase-velocity measurements of ambient-noise data

2020 ◽  
Author(s):  
Hamzeh Sadeghisorkhani ◽  
Ólafur Gudmundsson ◽  
Ka Lok Li ◽  
Ari Tryggvason ◽  
Björn Lund ◽  
...  
Keyword(s):  
Phase Velocity ◽  
Ambient Noise ◽  
Velocity Dispersion ◽  
Dispersion Curves ◽  
Upper Crust ◽  
Southern Sweden ◽  
Zero Crossings ◽  
Phase Velocity Dispersion ◽  
Cross Correlations ◽  
Velocity Bias

Summary Rayleigh-wave phase-velocity tomography of southern Sweden is presented using ambient seismic noise at 36 stations (630 station pairs) of the Swedish National Seismic Network (SNSN). We analyze one year (2012) of continuous recordings to get the first crustal image based on the ambient-noise method in the area. Time-domain cross-correlations of the vertical component between the stations are computed. Phase-velocity dispersion curves are measured in the frequency domain by matching zero crossings of the real spectra of cross-correlations to the zero crossings of the zeroth-order Bessel function of the first kind. We analyze the effect of uneven source distributions on the phase-velocity dispersion curves and correct for the estimated velocity bias before tomography. To estimate the azimuthal source distribution to determine the bias, we perform inversions of amplitudes of cross-correlation envelopes in a number of period ranges. Then, we invert the measured and bias-corrected dispersion curves for phase-velocity maps at periods between 3 and 30 s. In addition, we investigate the effects of phase-velocity bias corrections on the inverted tomographic maps. The difference between bias corrected and uncorrected phase-velocity maps is small ($&lt; 1.2 \%$), but the correction significantly reduces the residual data variance at long periods where the bias is biggest. To obtain a shear velocity model, we invert for a one-dimensional velocity profile at each geographical node. The results show some correlation with surface geology, regional seismicity and gravity anomalies in the upper crust. Below the upper crust, the results agree well with results from other seismological methods.

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