Site Period Characteristics across the Canterbury Region of New Zealand

The influence of multiple impedance contrasts on mHVSR site period estimates in the Canterbury Plains of New Zealand and implications for site classification

“…Several studies have collected recordings of microtremors, both in urban Christchurch and the surrounding Canterbury Plains, in efforts to improve the understanding of ground shaking in the region using results from mHVSR and/or other geophysical testing methods (Mucciarelli, 2011;Toshinawa et al, 1997;Wotherspoon et al, 2015Wotherspoon et al, , 2018. The details and experimental parameters for each of the microtremor datasets are summarized in Table 1 and were each considered for use in the present study.…”

“…Microtremor records up to 3 h long were collected for the passive surface wave testing and are well suited for mHVSR analysis. Wotherspoon et al (2015Wotherspoon et al ( , 2018 combined the microtremor data from the SMS studies, a study focused on the Heathcote Valley, and additional testing locations across the Canterbury Plains to develop a dataset of records with clear mHVSR peaks at 102 locations. In 2017-2018, ambient vibrations were recorded at an additional 50 locations, targeting southern Christchurch near the Banks Peninsula.…”

“…a rock site or a soil/gravel site with gradual increases in shear wave velocity), no clear peaks may be identified in the measured mHVSR spectra (Cha´vez-Garcı´a et al, 2007;Ryder et al, 2021). In complex depositional environments, such as the Canterbury Plains in New Zealand, the measured mHVSR periods associated with multiple impedance contrasts capture observed site effects better than V S30 or other site effects metrics alone (Mazzoni et al, 2014;Wotherspoon et al, 2015Wotherspoon et al, , 2018.…”

A VS30 Map for New Zealand Based on Geologic and Terrain Proxy Variables and Field Measurements

“…The “surface waves” data set refers to a compilation of V S 30 data from several surface wave analysis–based site investigations performed following the 2010–2011 Canterbury earthquake sequence (Cox et al 2011; Wood et al 2011, 2017; Wotherspoon et al 2013, 2016; Van Houtte et al 2014; Teague et al 2018). Cox et al (2011) compiled a rapid preliminary report of surface wave testing (multichannel analysis of surface waves (MASW)) performed in Christchurch after the 2010–2011 earthquake sequence along with inverted site profiles from which V S 30 estimates were obtained.…”

“…The sites’ V S 30 were inferred from surface wave–based methods using frequencies ≥ 14 Hz, meaning that V S 30 profiles could not be developed down to 30 m and assumptions were used. Wotherspoon et al (2016) report seven V S 30 values derived from surface wave–based site V s profiles measured in conjunction with work by Cox et al (2014). Deschenes et al (2018) provide these seven plus two additional V s profiles.…”