Site period estimations in the Fraser River delta using microtremor measurements - experimental and analytical studies

Abstract

SUMMARYThis paper presents site period investigations at nodes on a 1-km grid within a 6-km by 8-km area in Vancouver and Richmond, BC. The area includes a range of site conditions, and is selected as the pilot application area for an urban seismic instrumentation project (Canadian Urban Seismology Program -CUSP) undertaken by the Geological Survey of Canada (GSC). The pilot project area is situated in one of the most seismically active regions in Canada and part of it lies on thick deltaic sediments that are known to have amplified ground motions during past earthquakes. Reliable site response models for the area are needed to quantify the amplification potential. Microtremor measurements provide a relatively inexpensive and simple tool to obtain one of the key parameters in site response studies, the site period. A series of microtremor measurements in the pilot CUSP area yielded site periods ranging from 0.05 seconds at bedrock outcrop to 4.2 seconds at some sites on the Fraser River delta in Richmond. Site periods were also estimated using a 1-D site-modeling program, SHAKE, for sites on the Fraser River delta. Each site was represented by a simplified 3-layer model with Holocene deposits, Pleistocene deposits and bedrock. The highest site period obtained from SHAKE modeling was 4.4 seconds about 3 km east of Richmond City Hall, for which the microtremor measurements indicated a site period of 4.2 seconds.

Application of the HVSR Microtremor Method for Basalt Outcrops in Tanjung Batu, Jambi

“…thick sedimentary layers will give a small frequency value [7]. low value natural frequency due to thick surface sediment, while high values natural frequency due to thin sediment [8].…”