What is the Risk?
Although the seismic hazard in New York City is moderate, because of the potential occurrence of a unique set of factors, summarized by this equation, the risk to the area could be high due to the high cost of dealing with the repercussions of any earthquake damage in a congested city environment.
Moderate seismic hazard + High density & monetary value + Lack of seismic design (before 1995) = HIGH SEISMIC RISK
With nearly one million buildings, New York City’s risk is very high, largely due to the dense built environment and highly interconnected infrastructure.
Most buildings in New York City were built before 1995, when more stringent seismic provisions in the Building Code were adopted; so, many of the most common building types here, such as unreinforced masonry buildings, are particularly vulnerable to seismic events.
New York City’s newest commercial and residential buildings are built to modern seismic standards, which minimizes physical risk. Yet, the economic risk remains — real estate and new development sprouting across the boroughs is so valuable that the costs associated with repairing damage from an earthquake are extremely high.
Any event that interrupts the flow of business, transportation, tourism, or finance in New York City, poses the risk of a negative economic impact on domestic and international trading partners.
Unlike other natural hazards, earthquakes occur with little or no warning – a situation that places the local population at immediate risk. Since New Yorkers experience earthquakes less frequently than other natural hazard events, people might be at higher risk, because they are less likely to be prepared to respond to this type of emergency.
Earthquakes present a significant risk to public safety and health. A large-magnitude earthquake may cause significant injuries and casualties, disrupt emergency and medical services, and endanger individuals who depend on these services. Long-term health risks associated with earthquakes include post-traumatic stress disorder and a range of mental health problems, such as depression and anxiety.
A moderate (magnitude 5.5 to 6) earthquake such is possible in New York City could cause significant injuries and casualties. Mortality and injury typically peak within the first 72 hours following an earthquake. In a study of 1,100 fatal earthquakes around the globe, 75 percent of fatalities were caused by collapsing buildings.
According to FEMA, non-structural failures account for the vast majority of earthquake damage, causing serious injuries or fatalities and making buildings nonfunctional. Non-structural components (not part of a building's structural system) that cause risk include:
- Architectural components, such as cladding, windows, glass, and plaster ceilings
- Mechanical, Electrical, and Plumbing (MEP) components
- Furniture, Fixtures, & Equipment (FF&E) and contents, such as heavy picture frames, mirrors over beds, hanging plants, and heavy furniture (bookcases, filing cabinets, and china cabinets)
During an earthquake, these components may slide, swing, or overturn if they are not tightly affixed to the structure of the building. Theaters, libraries, and other large public areas often have plaster ceilings that are highly vulnerable to collapse when an earthquake shakes the building. Non-structural failures can cause fatalities, injuries, and property loss, and also block exit routes during emergencies.
In California and in other seismically active regions of the country, many homeowners understand earthquake risk and take precautions, such as securing shelfing to walls, anchoring valuable items, anchoring water heaters, and embarking upon additional mitigation efforts. In Eastern U.S. cities, residents rarely take these precautions, because they experience so few earthquakes and assume the risk is low.
Buildings (6 stories and taller) that have rooftop water towers are another risk in New York City. If an earthquake hits, water tanks can be toppled, disrupting water service to residents and potentially injuring pedestrians.
Destruction of roads, bridges, and tunnels as the ground shakes during an earthquake would trigger widespread injuries and fatalities. The disruption of and damage to infrastructure and other critical systems often has a cascading set of impacts. Ground shaking during earthquakes could generate fires, putting residents at significant risk. The disruption of transportation networks puts anyone who depends on them at risk and also hinders delivery of emergency and medical services. In an earthquake’s aftermath, health risks increase due to the potential for polluted water and diseases spreading throughout the community.
The time at which an earthquake occurs also influences its impacts. If an earthquake occurs on a weekday between 9 a.m. and 5 p.m., mortality rates rise, because people are more likely to be working in a large building and children are likely to be at school. If an earthquake occurs during the night, people are likely to be at home inside with their family members.
Damage to buildings after a moderate earthquake could force thousands of New Yorkers into interim housing or require permanent relocation for many people. This poses a challenge on where to locate interim housing because the surrounding region may be affected as well.
An earthquake can put New York City’s economy at risk, displacing and disrupting businesses and utilities, and impairing people's ability to work and generate income. Property owners are at risk of economic loss from the need for expensive repairs and the loss of rental income. Any downtime in New York City’s operation as a major global financial center potentially affects the entire world’s economy.
If important national monuments and landmarks are damaged during an earthquake, the psychological and cultural impact from damage to these icons would be felt across the entire nation.
Although earthquakes in New York City have a low probability, any potential damage here could be catastrophic due to the density and age of buildings and the inter-dependencies of complex layers of infrastructure.
New York City’s built environment consists of a unique concentration of commercial and residential high-rise skyscrapers and low-rise buildings that are largely made of unreinforced brick. Each building type has a very different risk profile according to its height, material, location, and foundation.
High-rise and Low-rise Buildings
The structural systems of New York City’s high-rise buildings are less vulnerable to earthquake damage than low-rise buildings. Large earthquakes with long-period waves tend to damage tall buildings; however, these categories of earthquake events are less likely to occur in New York City. Large-magnitude earthquakes that occur farther away from New York City, such as in Canada or the Midwest, can create low-frequency (slow-moving) shaking in the city that can affect tall buildings.
Buildings built according to the Department of Buildings 1995 building code and successive seismic regulations are expected to be capable to mitigate the impact of an earthquake. The regulations require buildings be designed, at minimum, to preserve human life if a major earthquake hits and to preserve general occupancy conditions if less severe earthquakes shake the building.
Unreinforced Masonry and Wood BuildingsStructures in New York that were not designed for earthquake loads are inherently vulnerable should seismic events occur. Unreinforced masonry (brick) buildings are most at risk, because masonry is unable to absorb tensile forces during an earthquake. Instead of bending or flexing, walls, facades, and interior structures break or crumble. During a strong earthquake, the structural support system of an unreinforced masonry building has an increased risk of collapse. The typical modes of failure are:
- Failure of the roof-to-wall connection with a resulting collapse.
- Out-of-plane (when forces are exerted perpendicular to the surface) failure of unreinforced masonry walls.
- In-plane failure of unreinforced masonry walls, when cracks develop in the plane of the wall.
New York City has over 200,000 multi-family, unreinforced brick buildings, most built between the mid-1800s and 1930s. All are between three and seven stories high. See graph indicating the high proportion of masonry building in New York City.
Brooklyn has the largest number of masonry buildings (165,661), followed by Queens (108,694), the Bronx (49,734), Manhattan (29.766), and Staten Island (7,041).
Many New York City neighborhoods consist of rows of attached unreinforced masonry buildings. The buildings rely on one other for stability, so any building that sits at the end of a block or next to a vacant lot is particularly vulnerable during an earthquake event. Masonry loft buildings, which are common in New York City, are vulnerable because they lack interior walls and have higher-than-average ceilings.
Because wood is a more flexible building material, wood frame buildings respond better to earthquakes. In New York City’s fire districts, buildings constructed with wood frames are required to have a masonry veneer (or larger distances between buildings). Most one- to two-family houses in New York City are wood frame construction. For these homes, an earthquake could damage the masonry façade, but the structure could still stand. However, for three- to four-story buildings with load-bearing masonry, the building’s stability could be compromised during an earthquake.
Even if an earthquake caused little damage above ground, damage to a building’s foundation could render it uninhabitable or unusable. A large portion of New York City's waterfront originated as wetland or wasteland that was filled in, reclaimed, and built up over time. During colonial times, this land was typically created by using fill with poor structural properties. A few decades ago, more controlled fill and construction procedures were applied.
New York City has recently adopted new guidelines to protect structures from flooding and has increased its resiliency by recommending that coastal buildings be elevated so that a soft story base permits floodwaters to pass through – for example, supporting the first floor on piers. However, during an earthquake, this combination of a soft story base and poor subsurface conditions could shift most of the building’s load to the foundation, concentrating most of the damage in the bottom story.
Source: FEMA, 2009
|"When unreinforced masonry buildings begin to come apart in earthquakes, heavy debris can fall on adjacent buildings or onto the exterior where pedestrians are located. The diagram on the left shows the failure of parapets, one of the most common types of unreinforced masonry building damage. This level of damage can occur even in relatively light earthquake shaking."|
Assessing Potential Earthquake Impacts on New York City Buildings
NYCEM uses FEMA’s HAZUS-MH software to project losses and to assess structural vulnerability of New York City buildings should an earthquake occur. The five overall damage state categories for the HAZUS-MH earthquake module are None, Slight, Moderate, Extensive, and Complete. The graphic explains the four structural damage states (Slight to Complete) for a single building class (in this case, Type W1-wood, light frame).
HAZUS-MH Earthquake Damage States
Source: HAZUS-MH Earthquake User Manual, Figure 9.17
To quantify New York City’s built-environment risk from earthquakes, NYCEM modeled the potential impact of a hypothetical earthquake scenario, assuming that the epicenter was in the same location as the August 10, 1884 New York City earthquake. This model, which utilized HAZUS-MH software, was adapted using the current New York City building stock and the Department of Finance data to assess building values.
The results show the number of buildings by construction type that would be affected in New York City under the four damage-state classifications. Unreinforced masonry and wood constructed buildings are more likely to be damaged, compared to all New York City buildings. For clarity, the numbers in this table are rounded to the nearest hundred buildings.
Number of Buildings Damaged from M 5.2 Earthquake
|Construction Type||Slight||Moderate||Extensive||Complete||Total Damaged||% of Buildings Damaged|
|Reinforced Masonry (RM)||900||500||80||0||1,480||4%|
|Unreinforced Masonry (URM)||9,400||4,300||800||100||14,600||44%|
The NYCEM analysis also generated a projection of the dollar losses and economic impact using the same 1884 earthquake scenario as used above. The table provides estimates of building damage, transportation and utility damage, and the level of service and care required for people. As shown, fires, wreckage, and debris removal are all consequences related to earthquake hazards. If the same 1884 magnitude earthquake were to occur today, New York City could expect economic damages to equal $4.7 billion dollars and 493,000 tons of debris. Areas that would experience the most economic loss to buildings include south Brooklyn, JFK airport, and Breezy Point in the Rockaways.
Summary of Deterministic Results Modeled on 1884 M 5.2 Earthquake
|Moment Magnitude||Building Damage (millions of dollars)||Transportation and Utility Damage (millions of dollars)||Total (millions of dollars)||Hospitalization (people)||Shelter Required (people)||Fires||Buildings Completely Damaged||Debris (tons)|
Source: NYCEM, HAZUS, and NYC Department of Finance 2018. *Assume that the earthquake occurred at 0200 HRS, which is the maximum casualties.
Direct Economic Loss to Buildings - Modeled on 1884 M 5.2 Earthquake
NYCEM GIS is in the process of re-calculating potential damages for return periods of 100, 500, and 2,500 years. The table below is from the 2014 Hazard Mitigation Plan, which is a placeholder until new models are completed. As with projections associated with every HAZUS-MH model, there are limitations to the loss estimates generated.
Summary of Probabilistic Results of NYCEM Study
|Return Period||Building Damage (billion)||Income Loss (billion)||Total (billion)||Hospitalization (people)||Shelter Required (people)||Fires||Debris (million tons)|
Source: NYCEM, 2003
If an earthquake occurs in New York City, there is a risk that its impact will compromise infrastructure such as bridges, tunnels, utility systems, dams, and highways. As part of other capital improvements being made here, some of New York City’s existing bridges have been partially retrofitted to improve their seismic performance.
However, the seismic vulnerability of the city’s complex network of interlinked infrastructure remains poorly understood and exists as an area of high concern, even as parts of the infrastructure undergo change, upgrade, and renewal. Some of New York City’s critical infrastructure systems are vulnerable because they have aged and have maintenance problems.
During an earthquake event, soil liquefaction could result in large-scale ground failure that damages pavements and building foundations and massively disrupts underground utilities. Areas with artificial fill are vulnerable to liquefaction and include JFK airport, the World’s Fair site in Flushing, Queens, and Chinatown in Manhattan. A seismic event could cause structures built atop liquefied soils to sink and settle. Damage to underground infrastructure usually occurs wherever pipes and other utility transmission lines are unable to withstand soil movements. Damage to these critical links could trigger secondary impacts that pose even greater risk to the public -- water contamination, fires, and sudden, powerful explosions.
Upstate dams, reservoirs, and aqueducts are also at risk of serious damage from an earthquake. Damage to these resources could affect the water supply to New York City businesses and residents, and could impede the ability to suppress fires in the metropolitan area following an earthquake.
Earthquakes can severely damage the natural environment, destroying trees and disrupting the landscape, which potentially diminishes the aesthetic value of beloved natural features.
Earthquakes also pose risks that could cause severe harm to the natural environment -- fires caused by gas pipe explosions, flooding and other disruption caused by broken water pipes, accidental releases of hazardous waste, and devastating landslides.
As New York City’s substantial stock of seismically vulnerable (pre-seismic code) buildings is gradually replaced with new structures conforming to more robust seismic building code specifications, the percentage of vulnerable buildings will gradually decline; however this would take a very long time. The dollar value of New York City’s vulnerability would be expected to decline as well; however, if the value and volume of New York City’s built assets increase over time, the economic risk from seismic exposure could still increase.
Aging components of New York City’s infrastructure could amplify the structural impacts of earthquakes in the future. Investments, such as improving the seismic performance of existing bridges, should reduce the risks from future earthquakes.