Delaney Park Downhole Array in Anchorage, Alaska—Site Properties Inferred From M7 Anchorage, Alaska Earthquake

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

We used waveforms from the moment magnitude (M) 7.0 Anchorage earthquake and six select aftershocks, ranging from M4.2 to 5.7, to quantify site properties including shear-wave velocity profile, predominant frequencies, site amplification, soil damping and shear modulus at Delaney Park in downtown Anchorage, Alaska. The waveforms were recorded by surface and six borehole (up to 61 m depth) three-component accelerometers. The deconvolution of the waveforms at various borehole depths on horizontal sensors with respect to the corresponding waveform at the surface provides incident and reflected traveling waves within the soil. The shear-wave velocities determined from these events are consistent, and agree well with the in-situ measurements. The site amplification based on surface-to-downhole traditional spectral ratio (SSR), response spectral ratio (RSR), cross-spectral ratio (c-SSR), and horizontal-to-vertical spectral ratio (HVSR) of the surface recordings was also evaluated. Based on c-SSR, we computed the site amplification as 4.8 at 1.35 Hz (0.74 s), close to the predominant frequency of the soil column. This amplification matches with the average amplification reported in and around Anchorage by previous studies.

Presenting Author: Erol Kalkan

Authors