A Global Mosaic Vs30 Map With Regional Map Insets

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

The shear wave velocity in the upper 30 meters of the earth’s surface (Vs30) is a key parameter for estimating ground motion amplification as both a predictive and diagnostic tool for earthquake hazards. However, site-specific Vs30 measurements are rather limited, so geospatial inferences are necessarily made to interpolate and map Vs30 estimates elsewhere. A first-order approximation of Vs30 is commonly obtained via a topographic slope-based or terrain proxy (wherein steeper slopes generally indicate greater Vs30 values and gentler slopes indicate smaller Vs30 values) due to the widely available nature of digital elevation models; the USGS has produced such a map for the globe (https://earthquake.usgs.gov/data/vs30/). However, better-constrained Vs30 maps have been developed in many regions that are preferable to proxy-based Vs30 maps. Regional and local Vs30 maps employ Vs30 measurements, higher-resolution slope, lithologic, geologic, geomorphic, and other proxies, and often utilize refined interpolation schemes to achieve more accurate maps. Here we describe the development of a new hybrid global Vs30 map that defaults to the global slope-based Vs30 map but smoothly insets openly-available, high-quality regional Vs30 maps. Regional inset maps presently include California, Japan, Taiwan, New Zealand, Australia, Italy, Greece, Iran and others. Comparisons of the default slope-based proxy with the mosaic version (with higher-quality inset maps) are presented in terms of Vs30 differences as well as resulting amplification ratios. We aim to update the map regularly with the hope that new Vs30 regional maps become publicly available. USGS serves the new global Vs30 maps online via an ArcGIS web service; the underlying source code is provided on GitHub (https://github.com/usgs/earthquake-global_vs30).

Presenting Author: David C. Heath

Authors