Figure S3a. Best-fit regression of decay in wave group velocity
with frequency (equations [1a] and [1b] in the main manuscript)
based on active seismic experiments for each of the 24 seismic sensor
locations. Each line is fitted through the average value of 20 repeated
sledgehammer impacts (see also Figure 5b in the main manuscript). The
thicker the line, the greater the number of seismic sensor locations
that share the same \(v_{p0}\) and \(\xi\) values (i.e. Table S3), from
a single seismic sensor location sharing the same parameter values (i.e.
thinner line), up to three seismic sensor locations sharing the same
parameter values (i.e. thicker line). Note that seismic sensor locations
presenting the same \(v_{p0}\) and \(\xi\) values were estimated based
on a single active seismic experiment encompassing multiple sensors
thanks to their geographical proximity. The parameters found by Bakker
et al. (2020) for an alluvial channel (in red), and proposed by Tsai et
al. (2012) for a generic bedrock site (in blue) are presented for
comparative purpose.