Estimating Site Velocity Characteristics for Strong Motion Stations in Anchorage, Alaska

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications
Type: Oral
Date: 4/28/2020
Time: 08:45 AM
Room: 110 + 140
Description: 

Site fundamental frequency has been used as a method to estimate site response in recent studies. Site fundamental frequency often is developed by horizontal to vertical spectral ratios (HVSR). In recent studies HVSR-based site fundamental frequencies have been utilized as a V_S30 proxy for sites where no V_S30 data exist for strong motion stations in less seismically active regions such as the Central and Eastern United States (CEUS) and more active regions including Iran. The initial research focused on sites where a strong impedance contrast was observed. Recently, Anchorage, Alaska experienced a M7.1 earthquake and over 30 strong motion stations recorded the event. However, only a few stations have V_S30 measurements or estimates. The HVSR-based site fundamental frequency and V_S30 data was used to select and verify the validity of the V_S30 proxy model as effective for Anchorage and was modified to account for the regional geology, where strong impedance between surficial soils and underlying glacial till exists. This proxy was then utilized, along with the local geologic conditions to extend a V_S30 estimate to the remaining strong motion stations to better estimate site response characteristics. At several sites, where geotechnical data was also available, V_S30 estimates were compared to the V_S30 proxy estimate.

Past research has also utilized topographic slope methods to estimate V_S30 at these sites. In general, topographic slope estimates have shown poor correlation to actual measured V_S30 estimates. The V_S30 proxy estimates are compared to the topographic slope methods. The differences between the two results highlight the importance of utilizing local subsurface conditions and geology to estimate site characteristics to better estimate site response characteristics. These updated estimates then provide a better estimate until actual site measurements are performed at these strong motion stations.

Presenting Author: John Thornley

Authors