Predicting Earthquake Damage in New Jersey

New Jersey Geological Survey

Information Circular Predicting Earthquake Damage in New Jersey

Damaging earthquakes are with the density and value of the standard, analyzes these factors to rare, but not unknown, in New buildings, place New Jersey tenth generate damage estimates. Jersey (fig. 1). Earthquakes with an among all states for potential eco- Soils influence damage in two estimated magnitude of 5.2 on the nomic loss from earthquakes. ways. Soft soils amplify the motion Richter scale occurred in the New Predicting the location and of earthquake waves, produc- York City area in 1737 and 1884. extent of damage is key to pre- ing greater ground shaking and In historic times, earthquakes with paring for earthquakes. Damage increasing the stresses on struc- magnitudes between 6 and 7 have depends on the location, depth, tures. Loose, wet, sandy soils may occurred in the Boston, Massachu- and magnitude of the earthquake, lose strength and flow as a fluid setts and Charleston, South Caro- the thickness and composition of when shaken (a process known lina areas, and in the St. Lawrence soil and bedrock beneath the area as liquefaction), causing founda- Valley of Quebec. New Jersey is in in question, and the types of build- tions and underground structures a similar tectonic setting as these ing structures. A computer model to shift and break. Mapping the places and earthquakes of this commissioned by the Federal ground-shaking and liquefaction magnitude are possible. The risk of Emergency Management Agency potential of soils is an essential a damaging quake, in combination (FEMA), now used as a nationwide component in predicting earth-

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Figure 1. Surficial geology of the Newark area (from Stanford, 2002a, 2002b) and location of historic earthquake epicenters in and near New Jersey. of swamp and salt-marsh peats vital transportation links, includ- �� that are now completely covered ing Newark-Liberty International �� by fill. Engineering data from the Airport, the New Jersey Turnpike, �� many boring logs provide informa- Interstate Route 78, the Amtrak �� tion on the density and compaction Northeast Corridor rail line, and of the sediments. the Port Newark marine terminal. This information was used The mapping and simulations to generate maps of liquefaction indicate that this is a priority area susceptibility and ground-shaking for strengthening vulnerable struc- � � � potential (fig. 2). Till, which -under tures. �� lies the western half of the city, is Similar soil mapping and �� compact and has low liquefaction earthquake simulations have been �� and ground-shaking potential. completed for Hudson, Bergen, �� Peat, deposited in wetlands, and Essex, and Union counties, and silt, clay, and fine sand deposited are planned for eight additional in floodplains and glacial lakes, counties, in northern New Jersey. are soft, saturated soils that are highly susceptible to shaking and References liquefaction. These underlie much Figure 2. Liquefaction susceptibil- of the eastern half of the city. Sand Stanford, S. D., 2002a, Surficial geology of the Orange quadrangle, Essex, Pas- ity and ground-shaking potential for and gravel deposited in glacial-lake saic, Hudson, and Bergen Counties, New Newark. deltas and river plains, which form Jersey: N. J. Geological Survey Open-File a narrow belt through the center of Map OFM 41, scale 1:24,000. quake damage. Ground-shaking the city, are of intermediate com- ______behavior is mapped by summing paction and have medium shaking 2002b, Surficial geology of the Eliza- beth quadrangle, Essex, Hudson, and physical measures of the density and liquefaction potential. Union Counties, New Jersey: N. J. Geo- and compaction of soil and rock logical Survey Open-File Map OFM 42, layers to a depth of 100 feet. Lique- scale 1:24,000. faction susceptibility is determined �� Wheeler, R. L., Trevor, N. K., Tarr, A. C., �� by the geologic history, depositional �� Crone, A. J., 2001, Earthquakes in and setting, and topographic position of �� near the northeastern United States, �� the soil. �� 1638-1998: U. S. Geological Survey Geo- �� Newark, New Jersey’s larg- logic Investigations Series Map I-2737, scale 1:1,500,000. est city, is built on glacial and postglacial deposits that overlie sandstone bedrock (fig.1). The glacial deposits include till, a compact �� sediment deposited beneath the �� glacier, sand and gravel deposited �� in glacial lakes and river plains, �� and silt and clay deposited in gla- �� cial lakes. The glacial deposits are Figure 3. Building damage in Newark �� as much as 250 feet thick. In places for a magnitude 5.5 earthquake. �� they are overlain by postglacial ��

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� terraces. The postglacial sediments west of the center of Newark, was �

� � are less than 20 feet thick. simulated on a computer using the � Data acquired during the geologic data outlined above. In the geological investigation of these simulation (fig. 3), less than 10% of �� deposits include soil observations the buildings underlain by till were �� at several hundred field stations, significantly damaged, whereas �� review of more than 800 boring and between 20 and 30% of those �� well logs, and archival maps that buildings underlain by wetland and �� show the extent of swamps and glacial-lake deposits were signifi- salt marshes prior to landfilling in cantly damaged. Utility pipelines �� the early 20th century. These data also suffer significantly increased �� permit mapping of the bedrock sur- damage on these soft, liquefiable �� face, the thickness and layering of soils. The vulnerable eastern sec- �� the glacial deposits, and the extent tion of the city contains within it ��