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Improving seismic hazard assessment in New England through the use of surficial geologic maps and expert analysis

TitleImproving seismic hazard assessment in New England through the use of surficial geologic maps and expert analysis
Publication TypeJournal Article
Year of Publication2012
AuthorsBecker, LR, Patriarco, SP, Marvinney, RG, Thomas, MA, Mabee, SB, Fratto, ES
JournalSpecial Paper - Geological Society of America
Pagination221 - 242
Date Published2012/01/01/
PublisherGeological Society of America (GSA) : Boulder, CO, United States
ISBN Number007210779780813724935
Keywords#StaffPubs, civil engineering, earthquakes, Eastern U.S., Engineering geology 30, Environmental geology 22, geologic hazards, mitigation, natural hazards, New England, Northeastern U.S., risk assessment, risk management, safety, seismic risk, seismicity, United States

(GSA Special Paper) In New England, earthquakes pose a risk to the built environment. Emergency preparedness and mitigation planning are prudent in this region as older unreinforced masonry buildings and numerous critical facilities are common. New England state geological surveys cooperate with the Northeast States Emergency Consortium (NESEC) to improve risk communication with emergency managers. To that end, Connecticut, Maine, Massachusetts, and Vermont employed surficial geologic maps, deglaciation history, knowledge of the glacial stratigraphy, and professional judgment to reclassify surficial geologic material units into one of the five National Earthquake Hazards Reduction Program (NEHRP) site classifications (A, B, C, D, and E). These new classifications were used as a substitute for the HAZards U.S. Multi-Hazard (HAZUS-MH) site class value of "D," which is used throughout New England as a default value. In addition, coding of surficial geologic materials for the five NEHRP site classifications was compared with classifications using the Wald methodology, a method that uses a slope analysis as a proxy for shear-wave velocity estimates. Comparisons show that coding to site classes using the Wald methodology underestimates categories A (high-velocity shear-wave materials, least relative hazard) and E (lowest-velocity shear-wave materials, greatest relative hazard) when evaluated side by side with coding done with the aid of surficial geologic maps. North of the glacial limit, derangement of drainage resulted in extensive ponding of meltwaters and the subsequent deposition of thick sequences of lacustrine mud. Inundation by the sea immediately following deglaciation in New England resulted in the deposition of spatially extensive and locally thick sequences of glacial marine mud. Surficial geologic maps better capture this circumstance when compared with the Wald topographic slope analysis. Without the use of surficial geologic maps, significant areas of New England will be incorrectly classified as being more stable than the site conditions that actually exist. By employing surficial geologic information, we project an improved accuracy for HAZUS-MH earthquake loss estimations, providing local and regional emergency managers with more accurate information for locating and prioritizing earthquake planning, preparedness, and mitigation projects to reduce future losses.

Short TitleSpecial Paper - Geological Society of America
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