EARTHSCOPE-DERIVED SINGLE-STATION REGIONAL SITE RESPONSE CORRECTION FACTORS FOR THE ATLANTIC COASTAL PLAIN

The 2011 magnitude 5.7 Virginia earthquake produced larger-than-estimated site response caused by the unconsolidated sediments of the Atlantic Coastal Plain (ACP), highlighting the need to improve earthquake site response estimates in the eastern United States. The horizontal-to-vertical spectral ratio (HVSR) method, using either earthquake signals or ambient noise as input, offers an appealing method for measuring site response because it uses only a single seismometer rather than requiring two or more seismometers traditionally used to compute a horizontal sediment-to-bedrock spectral ratio (SBSR) We analyzed teleseismic signals from the EarthScope Transportable Array, SouthEast Suture of the Atlantic Margin Experiment, Eastern North American Margin Array, and the DC Shake array and found a close match in the frequencies of the first primary resonance peaks (f₀) with both the SBSR and HVSR methods. The HVSR method estimates the amplitude of f₀ within a factor of 2 for ACP strata up to about 200 m thick, but consistently underestimates by a factor of ~5 the amplitude for ACP strata with thicknesses above about 200 m. Although previous studies show mixed results when comparing HVSR with SBSR methods, many of these studies were carried out on confined sedimentary basins that can generate substantial 3D basin surface wave effects. The strong bedrock reflector underlying ACP strata causes 1D resonance effects to dominate the site response estimates, with the amplitudes of the resonance peaks determined largely by the reflection coefficient at the base of the sediments. Here we present correction factors which offer a means to estimate regional site response amplifications from the ACP, or similar geologic environments, using the HVSR method utilizing a single seismometer. [This abstract represents the views of the authors and does not necessarily represent the views of the Defense Nuclear Facilities Safety Board.]