The Napa Valley Seismic Project is committed to the free education of passive seismic methods and towards developing a better understanding of Napa Valley geology.

This page is currently in development.

Seismic Glossary of Terms

Napa Valley Geology

USGS Napa Valley Geologic Map

Understanding Waves

Wavelet Modeler App by geo{DataScience}

Passive Seismic

View passive-seismic data (VS and HVSR) from all over the world with SeisImager.

Site Classifications

The International Building Code (IBC) has developed geologic site classifications, labeled A-E, for the use in structural engineering regulations designed to mitigate earthquake risk. Depending on the site classification of a site, certain structural building considerations will either be unwarranted or need to be made. This classifications is based on the averaged shear-wave velocity of the top 30 meters. Understanding the site classification code of a property, or for a large property, how the subsurface shear wave velocity (Vs) changes over distance and depth is very important. To learn more about site classifications, and their limitations, read our in-depth IBC Site Classifications – Explained.

HVSR – Nakamura’s Method

The Horizontal to Vertical Spectral Ratio (HVSR) is a passive-seismic method developed by Yutaka Nakamura and colleagues in the 1980’s. HVSR is a geophysical technique for estimating the resonance frequency and amplification of ground motions influenced by a surface layer. These influences on surface waves are calculated by dividing the (frequency) spectrum of the horizontal component by the spectrum of the vertical component of microtremors or earthquake motions. To collect HVSR data, a 3-component geophone is needed. Watch the video for a quick overview, or learn by visiting our HVSR Educational Webpage.