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- Title
Long Period Rayleigh Wave Focal Spot Imaging Applied to USArray Data.
- Authors
Tsarsitalidou, C.; Hillers, G.; Giammarinaro, B.; Boué, P.; Stehly, L.; Campillo, M.
- Abstract
We demonstrate the effectiveness of seismic dense array surface wave focal spot imaging using USArray data from the western‐central United States. We study dispersion in the 60–310 s period range and assess the image quality of fundamental mode Rayleigh wave phase velocity maps. We apply isotropic spatial autocorrelation models to the time domain zero lag noise correlation wavefield data at distances of about one wavelength. Local estimates of the phase velocity, its uncertainty, and the regression quality imply overall better ZZ relative to ZR or RZ results. The extension of the depth resolution compared to passive surface wave tomography is demonstrated by the inversion of three clustered dispersion curves from different tectonic units. We observe anisotropic surface wave energy flux and the influence of body wave energy, but sensitivity tests at 60 s targeting the data range, correlation component, and processing choices show that the ZZ focal spots yield consistent high‐quality images compared to regional tomography results in the 60–150 s period range. In contrast, at 200–300 s the comparatively small scales of the imaged structures and the imperfect agreement with low‐resolution global tomography results highlight the persistent challenge to reconcile imaging results based on different data sources, theories, and techniques. Our study shows that surface wave focal spot imaging is an accurate, robust, local imaging approach. Better control over clean autocorrelation fields can further improve applications of this seismic imaging tool for increased resolution of the elastic structure below dense seismic arrays. Plain Language Summary: Seismic tomography is an established imaging method that estimates properties of the medium using information of the seismic waves that propagate between source and receiver. This concept is routinely applied to earthquake waves and also to waves that are reconstructed using seismic noise correlations, and has led to impressive high‐resolution images in areas with high seismic sensor density. Here we apply an alternative imaging approach that has been developed in ultrasound medical imaging to surface wave data from the dense seismic USArray covering the western‐central part of the contiguous United States. In contrast to tomography the focal spot method does not analyze propagating waves but properties of the spatial autocorrelation field. The seismic wave speed and potentially other medium properties are estimated at the location of each seismic sensor using data obtained at other dense array sensors that are closely spaced in terms of the wavelength. The focal spot imaging technique is elegant and simple to implement because it does not involve the solution of an inverse problem. In this work we demonstrate its effectiveness by reproducing images from available USArray tomography results. Key Points: The local Rayleigh wave speed can be estimated from the focal spot, the time domain spatial noise autocorrelation field at short distancesWe use USArray focal spots to image the elastic velocity structure in the 60−310 s period range and compare the results to tomographyClean seismic dense array focal spots can enhance vertical and lateral resolution and feature detection for improved imaging
- Subjects
UNITED States; RAYLEIGH waves; SURFACE waves (Seismic waves); SEISMIC wave velocity; SEISMIC waves; SEISMIC tomography; SEISMIC arrays; EARTHQUAKE zones; MICROSEISMS; SEISMOLOGY
- Publication
Journal of Geophysical Research. Solid Earth, 2024, Vol 129, Issue 5, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB027417