Analysis of Spatial Variation of Seismic Ground Motions in the Anchorage Bowl From 30th November, 2018 Anchorage Earthquake (Mw 7.0)

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

An M 7.0 earthquake vigorously shook Anchorage, the largest city in the state of Alaska on 30th November, 2018. The quake was located about 14 km northwest of Anchorage and at a depth of 41.8 km on the subducting Pacific plate, underneath the North American plate. The ground motions were recorded by approximate twenty-five 3-component accelerometer sensors deployed at various parts of the Anchorage bowl covering major geological units. The maximum value of peak ground acceleration (PGA), with maximum 0.5 g is observed towards the southeastern part of the area, which clearly shows the influence of subsurface soil on the recorded ground motions. The spectral accelerations (SA), spectral velocity (SV) and the spectral displacement (SD) of the recorded ground motions are computed at each site in the interval between 0.04 sec to 15.0 sec. The maximum SA at periods of 0.2 sec and 1.0 sec are observed over the area dominated by the sensitive Bootlegger Cove Formations. The spectral displacement values are found to be well correlated with the observed damages at different parts of the area. The site response (SR) at each station site has also been computed from Fourier amplitude spectra of recoded S-wave motions of 10 s duration starting from the S-wave arrival, using the standard spectral ratio (SSR) and horizontal to vertical ratio (HVR) methods in the frequency range from 0.5 Hz to 10.0 Hz. The observed SSR values are averaged over two frequency bands namely Low-Frequency Band (LFB) and High-Frequency Band (HFB) with central frequency at 1.0 Hz and 5.0 Hz, respectively. A strong correlation between the spatial distribution of the average SSR at LFB and HFB and the local geology is noticed in the area.

Presenting Author: Utpal Dutta

Authors