  The horizontal-to-vertical spectral ratio (HVSR) method has become an
increasingly popular tool for developing a quick and reliable estimate of a
site's fundamental natural frequency ($f_0$). This paper presents HVSRweb, an
open-source, web-based application for performing HVSR calculations in a
convenient, reliable, and statistically-consistent manner. HVSRweb allows the
user to upload three-component ambient noise records and perform the HVSR
calculation in the cloud, with no installation required. The HVSR calculation
can be performed using a single combined horizontal component (e.g.,
geometric-mean, squared-average) or multiple rotated horizontal components to
investigate azimuthal variability. HVSRweb can reject spurious time windows
using an automated frequency-domain window-rejection algorithm, removing the
need for subjective and time-consuming user interaction. It also facilitates
the use of lognormal statistics for $f_0$, allowing for a consistent
statistical framework capable of quantifying measurement uncertainty in terms
of either frequency or its reciprocal, period. In addition, HVSRweb presents
the opportunity to rapidly incorporate new developments in processing and
quantification of uncertainty as they emerge, and encourages standardization of
HVSR processing across users while avoiding the challenges associated with
traditional approaches that require the user to perform regular updates to keep
pace with new developments.
