← Back to Sessions

Comparison of Site Amplifications Estimated Using Three Techniques in the Fort Worth Basin, Texas

Session: How Well Can We Assess Site Effects So Far? [Poster]

Type: Poster

Date: 4/21/2021

Presentation Time: 03:45 PM Pacific

Description: 

Following the development of unconventional oil and gas production across the Fort Worth Basin (FWB) in Texas, a rapid increase in seismicity across the basin began in 2008 that grew to include earthquakes affecting a substantial portion of the urban metropolitan area. In order to assess and mitigate the seismic hazard in the area, motivated by the thickness of the sedimentary basin and the accompanying soft soil layer, we estimate site effects at 22 seismic stations deployed to record these events. Site responses are derived using three different approaches: 1) a modified generalized inversion technique (GIT), 2) horizontal-to-vertical spectral ratio (HVSR), and 3) quarter-wavelength approximation (QWA). The site effects from the GIT and HVSR are based on the observed S-wave Fourier amplitude spectra from earthquake recordings, while the QWA is calculated using estimates of average shear wave velocities in the upper 30 m (V_S30). We find that site amplification estimates based on the three techniques are consistent with one another over resonance frequencies that range from 2.5 to 10 Hz. The mean amplification values from the three site factors are found to be on average about 3 times larger than the vertical site response derived from GIT, which is averaged to unity. These site amplification estimates also correlate with the geology proxy V_S30 determined by rock types and geologic age. Old and harder rocks (e.g., Pennsylvania limestone and sandstone) show lower site amplification while young and soft rocks indicate the higher amplification (e.g., Quaternary alluvium).

Presenting Author: SeongJu Jeong

Student Presenter: Yes

Authors