There is a growing need to characterize the engineering material properties of the shallow subsurface in three dimensions for advanced engineering analyses. However, imaging the near-surface in three dimensions at spatial resolutions required for such purposes remains in its infancy and requires further study before it can be adopted into practice. To enable and accelerate research in this area, we present a large subsurface imaging data set acquired using a dense network of three-component (3C) nodal stations acquired in 2019 at the Garner Valley Downhole Array (GVDA) site. Acquisition of this data set involved the deployment of 196 stations positioned on a 14 × 14 grid with a 5 m spacing. The array was used to acquire active-source data generated by a vibroseis truck and an instrumented sledgehammer, and passive-wavefield data containing ambient noise. The active-source acquisition included 66 vibroseis and 209 instrumented sledgehammer source locations. Multiple source impacts were recorded at each source location to enable stacking of the recorded signals. The active-source recordings are provided in terms of both raw, uncorrected units of counts and corrected engineering units of meters per second. For each source impact, the force output from the vibroseis or instrumented sledgehammer was recorded and is provided in both raw counts and engineering units of kilonewtons. The passive-wavefield data include 28 h of ambient noise recorded over two nighttime deployments. The data set is shown to be useful for active-source and passive-wavefield three-dimensional imaging and other subsurface characterization techniques, which include horizontal-to-vertical spectral ratios (HVSRs), multichannel analysis of surface waves (MASW), and microtremor array measurements (MAM).
Empirical transfer functions (ETFs) between seismic records observed at the surface and depth represent a powerful tool to estimate site effects for earthquake hazard analysis. However, conventional modeling of site amplification, with assumptions of horizontally polarized shear waves propagating vertically through 1D layered homogeneous media, often poorly predicts the ETFs, particularly, in which large lateral variations of velocity are present. Here, we test whether more accurate site effects can be obtained from theoretical transfer functions (TTFs) extracted from physics-based simulations that naturally incorporate the complex material properties. We select two well-documented downhole sites (the KiK-net site TKCH05 in Japan and the Garner Valley site, Garner Valley Downhole Array, in southern California) for our study. The 3D subsurface geometry at the two sites is estimated by means of the surface topography near the sites and information from the shear-wave profiles obtained from borehole logs. By comparing the TTFs to ETFs at the selected sites, we show how simulations using the calibrated 3D models can significantly improve site amplification estimates as compared to 1D model predictions. The primary reason for this improvement in 3D models is redirection of scattering from vertically propagating to more realistic obliquely propagating waves, which alleviates artificial amplification at nodes in the vertical-incidence response of corresponding 1D approximations, resulting in improvement of site effect estimation. The results demonstrate the importance of reliable calibration of subsurface structure and material properties in site response studies.
more » « less- Award ID(s):
- 1664203
- PAR ID:
- 10526791
- Publisher / Repository:
- Seismological Society of America
- Date Published:
- Journal Name:
- Bulletin of the Seismological Society of America
- Edition / Version:
- 4
- Volume:
- 111
- Issue:
- 4
- ISSN:
- 0037-1106
- Page Range / eLocation ID:
- 2042 to 2056
- Format(s):
- Medium: X Size: 4.4MB Other: pdf
- Size(s):
- 4.4MB
- Sponsoring Org:
- National Science Foundation
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