Multipathing Rayleigh Waves From Long‐Distance Noise Cross Correlation Along an Ocean‐Continent Boundary (Alaska to California)

Abstract

Seismic interferometry can reliably extract interstation surface waves in homogeneous or smooth media. We test the validity of this technique in the case of sharp lateral heterogeneity, by examining paths along the western edge of continental North America. After cross correlating several years of time series of ambient seismic noise, we extract interstation Rayleigh waves with different arrivals in the frequency of 0.04 to 0.06 Hz (periods 17 to 25 s). Using beamforming and seismic wavefield simulations, we show that the different Rayleigh wave arrivals are related to the oceanic and continental paths, respectively. This multipathing of Rayleigh waves that is identified from ambient noise is also identified from earthquakes. Our results demonstrate that seismic noise interferometry is capable of extracting realistic surface waves for complex structural paths such as along the continental margin of North America. Additional studies from other regions may demonstrate the potential for using multipathing surface waves within full waveform inversion.

Automatic Slowness Vector Measurements of Seismic Arrivals with Uncertainty Estimates using Bootstrap Sampling, Array Methods and Unsupervised Learning

“…For each arrival, we mark the path from the mean station location along the mean backazimuth (dashed white line inFig 9)to determine a possible cause for the multipathing. Also shown are the paths showing the backazimuth uncertainty bounds (solid white lines inFig 9), which suggest it is reasonable to hypothesise possible causes of the measurements.The top and middle paths may come from interactions with the boundary between the continental and coastal regions, which agrees with the interpretation ofXia et al (2018). The direction of the western most arrival suggests it could be caused by interacting with a coastal-ocean velocity Example application of the method for identifying multipathing in surface waves.…”

“…From this observation, the phase velocities and backazimuths of the multipathed arrivals can be measured and analysed with uncertainty bounds. Xia et al (2018) would be needed to recover the anisotropic properties, but this example shows how our technique can be used to identify statistically significant differences in phase velocity measurements.…”

“…Seismic array techniques which measure the full horizontal slowness vector (backazimuth and inclination) of seismic arrivals have been used to investigate Earth structure for decades. These analyses have been applied to a wide variety of seismic arrivals and problems such as by using long period surface waves to identify upper mantle and surface heterogeneity (Ji et al, 2005;Maupin, 2011;Xia et al, 2018), short period S-waves to analyse lower mantle structure (Cottaar & Romanowicz, 2012;Schumacher & Thomas, 2016;Stockmann et al, 2019;Ward et al, 2020), high-frequency P-waves to study scatterers in the mid and lower mantle (Niu & Kawakatsu, 1997;Thomas et al, 2002;Cao & Romanowicz, 2007;Frost et al, 2013;Bentham & Rost, 2014;Yang & He, 2015;Ritsema et al, 2020), event detection and spatial location (Chevrot et al, 2007;Landès et al, 2010;Liu et al, 2016), ambient noise (Behr et al, 2013;Roux & Ben-Zion, 2017), nuclear test spatial location (Bowers & Selby, 2009;Assink et al, 2018) and meteorological event spatial location (Gerstoft et al, 2006(Gerstoft et al, , 2008.…”

Crustal Structure of the Collision-Subduction Zone in South of Iran Using Virtual Seismometers

“…3). It is assumed that the records do not include multi-pathing from source to receivers ( 29 and 30 ). The earthquake waveforms (for each stationary station) are firstly prepared using the common low-frequency technique outlined in 28 .…”