Research Abstract
It is commonly accepted that the horizontal-to-vertical spectral ratio (HVSR) technique enables the detection of the
fundamental resonance frequency (fHVSR) of a given site. The
utility of this fHVSR is analyzed using the nonlinear regression
relationships between fHVSR and bedrock depth (h). The derived
relationships are mostly site-specific, so that the present paper
consists of two main parts. The first is a literature review for the
available empirical relationships between fHVSR and h. The aim of
this part is to highlight the practical limitations of these established
relationships and to make fair comparisons. The second is to
generate new relationships, taking advantage of the very wide
range of available lithological, geophysical, and geotechnical
borehole drilling data of the 697 KiK-NET seismic stations in
Japan. For this purpose, HVSR are calculated using 10,000 weak
earthquakes or linear events recorded at KiK-NET stations to
determine the fHVSR and correlate it with the corresponding h. The
overlying layers/bedrock interface falling within sedimentary,
igneous, or metamorphic layers significantly affect the derived
frequency–depth relationships. In addition, these relationships are
strongly reproduced by the Vp=Vs ratio of the bedrock in the range
of 1.6–2.2. Interestingly, it is found that fHVSR less than 1 Hz
corresponding to h more than 100 m leads the trend of the overall frequency–depth relationship.
