T108 Geologic Maps, Digital Geologic Maps, and Derivatives from Geologic and Geophysical Maps (Posters)

Monday, 1 November 2010
8:00 AM - 6:00 PM
Hall D

A COMPARISON OF DIGITAL Vs30 CLASSIFICATION MAPS FOR ALBUQUERQUE, NEW MEXICO: RESULTS FROM 62 SITE-SPECIFIC IMASW Vs30 SURFACE SURVEYS VS. U.S. GEOLOGICAL SURVEY TOPOGRAPHIC-BASED Vs30 MAP SERVER

Paper number: T108-42
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

30-meter average shear wave velocity (Vs30) estimates are now often used in ground motion prediction equations to characterize ground shaking hazards during seismic events. Vs30 measurements were collected at 62 sites in and around Albuquerque, New Mexico using interferometric multi-channel analysis of surface waves (IMASW) survey techniques in June, 2010. The site-specific Vs30 profile data were assigned to geologic units from the “Preliminary Geologic Map of the Albuquerque – Rio Rancho Metropolitan Area and Vicinity, Bernalillo and Sandoval Counties, New Mexico “ (Connell, 2006) by correlating the measured shear-wave velocity values to geologic units that are similar in age, physical characteristics, and depositional processes to create a regional Vs30 map.

We present a comparison of the Vs30 map based on 62 site-specific Vs30 values to a Vs30 map derived from the U.S. Geological Survey’s (USGS) Global Vs30 Map Server (Wald and Allen, 2007) which uses topographic slope to create a first order assessment of Vs30 in active geologic environments. Preliminary results indicate an approximate 50% match in classification within the 1-sigma error. A percentage of the remaining unmatched values can be attributed to geologic conditions which cannot be evaluated by topographic slope alone, including shallow flat-lying Holocene basalt flows, clast-supported gravel-cobble units characteristic of Rio Grande axial-fluvial deposits, and progressive development of carbonate cement in older Pleistocene piedmont and alluvial units.

This study reveals that in geologically complex regions site-specific Vs30 field measurements and geologic interpretation can be use to augment and substantially improve the results of modeled Vs30 values based on topographic slope alone.