Inversion of Earthquake-HVSR in the Anchorage Basin, Alaska, for Delineation of Shallow Sedimentary Structures
Description:
The Anchorage strong-motion network has been operational in and around Anchorage, Alaska, since 1995. The stations are primarily Kinemetrics force-balanced accelerometers with sampling rates of 200 Hz. Many seismological studies have been conducted using the recorded data collected from these stations. An earlier study utilized strong-motion records of 95 earthquakes of magnitude 4.5 and above between 2004 and 2019, including the November 30, 2018, MW7.1 Anchorage Earthquake, to compute the earthquake horizontal-to-vertical-spectral-ratio (e-HVSR) at 35 strong-motion stations across Anchorage. A total of 1,727 three-component recordings were used for the e-HVSR analysis. These records were processed, and the e-HVSR was calculated for each station over the 0.25–10 Hz frequency range. In this study, an inversion of the e-HVSR data from each strong-motion station was performed to obtain a 1-D layered earth soil profile for understanding the subsurface characteristics at individual sites. The inversion searches for models that satisfy least-squares fit criteria using a very fast simulated annealing algorithm and selected statistical tools, e.g., parameter correlation matrix and marginal posterior probability density function for quantitative assessments of each model. Where available, shear wave velocity data from the shallow boreholes were set a priori during the inversion analysis. The inversion results indicate the presence of higher-velocity (400–550 m/s) sediments at a relatively shallow (10–20 m) depth in the eastern part of the basin, at the foothills of the Chugach Mountains, in comparison to the western and northwestern parts of the Anchorage area. The inversion modeling of the e-HVSR results from the sites on the western and northwestern sides indicates sediments with lower shear wave velocities (250 –350 m/s) at 30-50 m depth. A detailed analysis of the 1-D inversion results and a comparison to the local geology is also presented.
Session: How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far? [Poster Session]
Type: Poster
Date: 5/1/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Utpal
Student Presenter: No
Invited Presentation:
Authors
Utpal Dutta Presenting Author Corresponding Author udutta2@alaska.edu University of Alaska Anchorage |
John Thornley john.thornley@wsp.com WSP Global |
Zhaohui (Joey) Yang zyang2@alaska.edu University of Alaska Anchorage |
Yue Zhao yzhao8@alaska.edu University of Alaska Fairbanks |
William Stephenson wstephens@usgs.gov U.S. Geological Survey |
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Inversion of Earthquake-HVSR in the Anchorage Basin, Alaska, for Delineation of Shallow Sedimentary Structures
Session
How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far?