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Achieving Deep Site Characterization in Greater Vancouver, British Columbia, Canada

Description: 

Towards achieving seismic microzonation hazard mapping for Greater Vancouver, British Columbia, site characterization data collection spans 5 years and multiple non-invasive seismic field methods (https://metrovanmicromap.ca). This presentation focuses on our efforts to achieve deep (~1 km) shear-wave velocity (Vs) depth profiling at 6 large seismic array sites. Sites are selected to target Vs of the overlying 100’s of meters of post-glacial or glacial sediments and into the underlying glacial sediments or rock, respectively. There are no Vs (some Vp) measurements of these deeper geologies in the region. All 6 large array sites are chosen based on our previous smaller-scale multi-method seismic data collection, i.e., previous Vs profiling achieved in the upper 10’s to 100’s of meters. We developed 13 seismometer deployment kits consisting of a DiGOS Data-Cube³ digitizer, three-component 4.5 Hz geophone, external battery, GPS antennae, with metal chain and lock of the plastic housing for minimal security. At each large array site, two simultaneous ambient vibration arrays each consisting of 6 sensors with a 13^th central sensor of 0.5 to 2 km circumradii were performed for a duration of 2-4 hours to obtain low frequency Rayleigh wave dispersion estimates, i.e., 3-4 arrays are accomplished per site over the field day. We present our preliminary one-dimensional dispersion analyses of these data; future analyses will treat the data in three dimensions. We obtain dispersion estimates that transition into the higher velocity underlying layer at depth, albeit with significant variability (resolution error). We present the first kilometer(s) deep constrained Vs profiles for Greater Vancouver. This work is in combination with an ambient noise tomography experiment in which we deployed the 13 seismometer kits with 5 other broad-band seismometers across Metropolitan Vancouver for 60 days to update our three-dimensional Vs model beneath Greater Vancouver.

Session: From Sensors and Networks to Site Characterization and Site Response: Coming Full Circle

Type: Oral

Date: 4/18/2023

Presentation Time: 10:45 AM (local time)

Presenting Author: Sheri Molnar

Student Presenter: No

Invited Presentation: 

Authors