Although New York City does not sit on a major fault system, like the San Andreas in California, earthquakes are possible here.
The likelihood that a strong earthquake will occur is moderate, but the risk is heightened by New York City’s population density, the scale of its built environment, the interdependencies of its critical infrastructure systems, the age of its infrastructure, and the high proportion of buildings that were built before seismic design provisions were adopted in City building codes in 1995.
In the future, the impact of any earthquake affecting New York City should be diminished due to improved building construction codes and infrastructure replacement initiatives.
What is the Hazard?
An earthquake is a sudden, rapid shaking of the earth as tectonic plates shift, rock cracks beneath its surface, and large plates either collide or try to push past one other. As rocks and the earth’s plates are strained by these tremendous geological processes, energy builds up under the earth’s surface. Eventually, accumulated energy deep underground becomes so great that it is abruptly released in seismic waves.
From this source, or “focus,” deep underground, the waves travel away and shake the earth’s surface. An earthquake’s epicenter is the point on the earth’s surface that lies directly above the focus. Seismologists and engineers measure the shaking that occurs as “ground acceleration.”
The intensity of ground shaking depends on several factors, including the amount of released energy, the depth of the earthquake beneath earth’s surface, the distance from the fault, and the type of underlying soil or bedrock.
How intensely a built structure responds to shaking during an earthquake depends on the building’s height, weight, and design.
An earthquake has the potential to damage and destroy buildings and a city’s infrastructure and take lives. Under certain conditions, earthquakes can trigger landslides and cause soil liquefaction. The latter occurs when shaking and ground vibration during an earthquake cause unconsolidated, water-saturated soils to soften and turn fluid. Ground shaking, landslides, and liquefaction together can damage or destroy buildings, disrupt utilities, trigger fires, and endanger public safety.
Aftershocks are part of the earthquake’s sequence that follows the largest, initial earthquake shock. Aftershocks are typically less intense than the main shock, and may occur for weeks, months, or years after the initial earthquake event.
Earthquake size is classified according to a magnitude scale that expresses the energy released at the earthquake’s source. Seismographs and other scientific tools are used to measure and record data to understand the severity of each tremor in the earth and the severity of each earthquake event. In the past, earthquake tremors were ranked according to the Richter scale, but in the 1970s, the scientific community began to use the more accurate Moment Magnitude scale. The Moment Magnitude scale measures the size of an earthquake at its source in regard to the size of the fault and the degree to which the fault is displaced. It is a logarithmic scale — each point that an earthquake’s magnitude increases on the scale represents an energy release that is 32 times larger than the point that precedes it.
The 2011 Virginia earthquake, which rattled the ground as far away as New York City, was a magnitude 5.8. By comparison, the 2011 earthquake that created such damage to the eastern coast of Japan was a magnitude 9.0 and considered catastrophic. In theory, these earthquake magnitude scales do not have an upper limit, but no earthquake event has yet reached a magnitude of 9.5. The Modified Mercalli Intensity (MMI) scale is a measurement based upon what has been observed in seismic shaking during earthquakes. The MMI reflects twelve categories of intensity based on people’s reactions, their observations, and building damage during seismic events.
The Modified Mercalli Intensity Scale
On August 10, 1884, New York City experienced its most severe earthquakes, which were estimated to have a magnitude of 5.2 on the Richter scale. On the MMI scale, the reported maximum intensities of the 1884 earthquake would correlate to Levels VI to VII. Experts also use quantitative methods to describe earthquake severity, such as Peak Ground Acceleration (PGA). PGA is an expression of the ground’s maximum acceleration as it shakes and moves during an earthquake and can be described by its changing velocity as a function of time. Acceleration is an important way to measure and discuss the intensity of an earthquake, because many seismic building codes incorporate it into better, more effective guidelines for building construction. Building codes stipulate, for example, the amount of horizontal inertial force (or mass times the acceleration) that buildings should be able to withstand during an earthquake without life-threatening damage. PGA is expressed as a percentage of acceleration and the force of the earth’s gravity (%g). A very strong earthquake, such as 1994’s magnitude 6.7 earthquake near Los Angeles, produces PGAs of over 100%g in the horizontal direction, which is greater than acceleration due to gravity. The effect of 100%g horizontal acceleration is similar to holding a building by its foundation and turning it on its side for a moment. The table below shows the approximate relationship between MMI and PGA near an earthquake epicenter.
PGA continues to be an important ground-shaking measurement; however, Spectral Acceleration (SA) is the ground-motion measurement unit commonly used today in modern seismic building codes. Compared to PGA, SA is considered to be a better indicator of damage to specific building types and heights. SA reflects how buildings of particular masses, heights, and structural stiffness (and related natural response period) react to being shaken by an earthquake.
How to Model a Building’s Spectral Acceleration (SA)
In a simplified manner, a building is represented by an inverted pendulum of a certain mass on a mass-less vertical rod that replicates the building’s natural period of vibration and the mechanical damping.
A very approximate rule for the natural spectral period Tb (seconds) of a building as a function of the numbber of stories n in the building is as follows: Tb (sec) = 0.1n
For example, a two-story building tends to have a natural period of about 0.2 second (frequency of 5Hz), whereas a ten-story building tends to have a natural period near Tb=1 second (frequency of 1 Hz)
PGA is also used to understand more about the types of earthquake hazards that are likely. The U.S. Geological Survey (USGS), which studies seismic conditions nationally, produces maps that indicate where future earthquakes are most likely to occur, how frequently they might occur, and how hard the ground may shake (PGA).
These maps estimate the probability that ground shaking, or ground motion, will exceed a certain level in 50 years.
In comparison to the previous map, the latest USGS maps, released in July 2014, show that larger, more damaging East Coast earthquakes are more likely to occur in the NYC area. The USGS map here shows that New York City has a moderate seismic hazard.
Strong earthquakes in New York City have not been registered, but moderate-magnitude earthquakes are possible. Even if an earthquake’s epicenter is far from New York City, the geology underlying the Northeast United States can cause some ground shaking to be felt right here.
When an earthquake occurs, the older, harder bedrock of the Northeast generates high-frequency motions that can travel long distances before they subside. For example, tremors from the 2011 earthquake in east-central Virginia and the 2013 earthquake along Canada’s Ottawa River were felt by many people in the eastern United States, including New York City. The 2011 Virginia earthquake, which had Moment Magnitude of 5.8, was felt more than 500 miles from its epicenter, making it the most-felt earthquake in modern U.S. history.
If an earthquake occurs in New York City, the unique geologic characteristics of the metropolitan area could result in significant effects due to soil amplification. The two main factors contributing to soil amplification here are the sharp contrast between softer soils and very hard bedrock, and the bedrock motions, which are expected to be relatively short and shake with high frequency.
High-frequency shaking is more common in the bedrock of Eastern United States and typically affects short, two- to five-story masonry buildings. A shallow layer of soft soil (less than 100 feet in depth) sits atop hard bedrock, so shaking is amplified but only for a relatively short period of time. By contrast, a high-rise building atop deep soil deposits will shake longer and shake more slowly during an earthquake.
Subsurface conditions in New York City, which vary widely across the five boroughs, can affect the degree to which an earthquake’s ground motion is amplified. As shown on this map, geologic conditions range from solid bedrock at ground surface (green) to artificial fill (purple).
For centuries, large areas of the New York City have been filled to cover soft sediments and marshes to create new space for building development. For example, Manhattan’s present-day Chinatown is on land created by filling in a large pond; the World’s Fair Park site in Flushing, Queens was built on an ash dump; and JFK Airport on Brooklyn’s south shore was built atop a hydraulic sand fill.
Between 1700 and 1986, over 400 earthquakes with a magnitude of 2.0 and above have been recorded in New York State.
Between 1973 and 2012, New York State had only two damaging earthquakes with magnitude of 5.0 and above. Historically, larger earthquakes have a longer “return period” in New York City. That is, they happen much less frequently than smaller earthquakes.
On August 10, 1884, one of the strongest earthquakes happened near New York City somewhere between Brooklyn and Sandy Hook, New Jersey. Based on contemporary reports of its damage, scientists today estimate it to have been a magnitude 5.2 earthquake. Although considered moderate by today’s magnitude scales, the shaking from this earthquake event was felt from Virginia to Maine, damaging chimneys and brick buildings in New Jersey and New York City. Considering the amount of building and development along the Hudson and in New York City since 1884, if the same magnitude earthquake occurred today, the amount of damage to people and property would be far worse.
The historical earthquakes map shows the distribution of earthquake epicenters throughout the tri-state area from 1737 to 2014. Note that this map shows only approximate locations of epicenters for pre-1973 events; also, not every pre-1973 earthquake event is included on the map.
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.
High Seismic Risk Equation
High Seismic Risk = Moderate Seismic Hazard + High Density & Monetary Value + Lack of Seismic Design (Before 1995)
With approximately 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 which 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)[xii]
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 shelving 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. Historically, 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 city has limited housing options, and 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, landmarks, cultural heritage and arts institutions housing artifacts of great significance are damaged during an earthquake, the psychological and cultural impact from damage to these icons would be felt across the entire nation or perhaps internationally.
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 New York City Department of Buildings (DOB) 1995 building code and successive seismic regulations such as the 2008, 2014 and 2022 New York City Building Codes, which include a chapter for structural requirements, 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 Buildings
Structures 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 100,000 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.
As of 2019, 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 another 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 adopted 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.
“When reinforced 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.”
-Rutherford & Chekene
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).
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 New York City 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 Earthquake
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 $97 million dollars and 17,200 thousands of 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 Earthquake
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.
How to Manage the Risk?
Even though earthquakes hit without warning and cannot be prevented, many strategies can be used to reduce the risks associated with them. Risk-mitigation strategies continue to grow more successful as seismologists, geologists, engineers, architects, emergency responders, and other experts innovate new public-safety initiatives in their respective fields.
The primary strategies involve more robust building code seismic requirements, enhanced seismic design requirements, and increased effort to inspect and maintain critical infrastructure.
NYC’s approach to risk management:
Protecting Buildings: Regulations, Enforcement, Engineering Strategies, and Maintenance
The 2023 earthquakes in Turkey and Syria brought renewed attention to the importance of building codes and proper enforcement. In New York City, DOB develops and updates building codes to mitigate risk from earthquake events and enforces them through extensive administrative measures. The seismic regulation follows the developments and improvements in national seismic standards.
Since 1985, FEMA has sponsored earthquake engineering research by the National Earthquake Hazards Reduction Program (NEHRP). Their latest (2009) publication FEMA P-750: NEHRP Recommended Seismic Provisions for New Buildings and Other Structures is the primary source of national seismic design requirements for new buildings and other structures[xv]
The goal of the NEHRP recommendations is to assure that building performance will:
- Avoid serious injury and loss of life
- Avoid loss of function in critical facilities
- Minimize costs of structural and nonstructural repair where practical
New York City’s current building code is as stringent as any in the United States, with the likelihood of failure or collapse of a modern, code-compliant structure being the same as that in California. Codes provide general occupancy conditions for less severe earthquakes. Any existing building in New York City that undergoes substantial modification is also required to adhere to these standards.
The Evolution of Seismic Building Code Provisions
The first seismic provisions in New York City’s Building Code were signed into law in 1995 and took effect in February 1996. The DOB further addressed the city’s structural vulnerability to earthquakes in 2008 and subsequently in 2014 and 2022, when it adopted the International Code Council’s family of codes as the basis of the New York City Construction Codes. It’s important to note that while the NYC Construction Codes adopted the ICC codes, they also amended some portions to be more stringent than the ICC.
The 2008, 2014 and 2022 Codes aim to make buildings stronger, more flexible, and more ductile – able to absorb energy without breaking in a brittle manner. The Codes have sections on soil types and building foundations. Seismic detailing is required to enable a building’s joints, structural connections, and piping to hold up during an earthquake.
Under the 2008, 2014 and 2022 Construction Codes, critical facilities such as firehouses and hospitals were required to be designed to both survive an earthquake event and to also remain open and functional following one.
In 2014, the DOB revised the Construction Codes and moved toward a new concept — the risk-based approach, following the model of the American Society of Civil Engineers Standard 7-2010 for designing and constructing seismic-resistant structures. In a similar manner, the 2022 Code follows the model of ASCE 7-2016. These enhanced codes require that new buildings in New York City are designed so it is less likely they will collapse or sustain significant damage during an earthquake.
The revised code also strengthens the design requirements for soil liquefaction and takes the city’s unique geologic conditions into account. Building designs must account for site-specific soil conditions and building foundations, and must ensure that joints and structural connections are flexible. Special detailing for electrical and mechanical systems, building contents, and architectural components are also specified.
Code committee work is now in progress for the next revision to the construction codes. DOB is also working on a draft of the NYC Existing Building Code, which includes a structural chapter intended to address issues related to seismic loads in existing buildings, among other concerns, by referring the user to the NYC Building Code structural requirements. This initiative aims to improve safety or mitigate hazards in buildings constructed before the seismic requirements were enacted.
To make sure that buildings are built to code, new construction and major renovations cannot begin until the DOB has reviewed plans and issued work permits. Most of the details required by earthquake design are subject to special inspections performed by qualified private engineers and responsible to report findings to DOB.
Engineering Strategies for Retrofit of Existing Buildings
To meet seismic standards, architects and engineers employ several methods to design and engineer the retrofit of older buildings — strengthening connections among building elements, increasing the structure’s flexibility, reducing building mass to minimize impact from seismic forces, and strengthening foundations placed in poor soil to ensure stability.
For existing unreinforced masonry buildings, connections between structural elements are strengthened by anchoring walls to the roof and walls to the foundation, thus increasing the structure’s ability to transfer loads during an earthquake. Another approach is to add steel frames to unreinforced brick walls to increase resistance to out-of-plane forces.[xvii]
Parapets are often the most damaged element of unreinforced buildings. Seismic risk can be reduced by anchoring parapets with bolt diagonal steel struts and repairing their mortar. Alternatively, unreinforced masonry parapets can be replaced by masonry parapets anchored to the building.
Simple, commonsense solutions are often enough to improve the seismic performance of a structure and to reduce the seismic risk. For example, anchoring or bolting furniture to a wall reduces the risk that the contents of a building will be damaged when an earthquake shakes it. Anchoring water tanks on buildings that are 6 or more stories is another method to reduce the risk that the tower topples over potentially injuring pedestrians and preventing the loss of water service to the building’s occupants.
Guidelines written to protect coastal buildings from flooding and coastal storms also discuss seismic safety issues, in particular, the vulnerabilities of elevated buildings. To protect buildings with a soft story base, solutions are to lessen the extra load by adding bracing or shear walls, or to enlarge or strengthen the columns and piles.
Routine maintenance on all buildings in New York City is essential to minimize the risks associated with earthquakes. This includes keeping roofs secure and in good condition, securing cornices and aluminum panels, repointing mortar regularly (especially on parapets and chimneys), and fixing all cracks.
Protecting Infrastructure: Government Guidelines, Inspections, and Engineering Strategies
Earthquakes can cause major damage to infrastructure that was not originally designed to withstand earthquake impacts – older bridges, tunnels, sewers, water supply systems, and wastewater treatment plants. New York City is acting to mandate that new infrastructure be designed to meet more robust seismic loading requirements, and that older infrastructure be retrofitted to meet those standards. Federal, state, and local government agencies all play roles in setting standards for and managing implementation of seismic safety improvements for infrastructure.
Seismic guidelines for infrastructure govern New York City’s actions in retrofitting older bridges, tunnels, and other critical facilities to withstand risks from earthquakes, and designing new infrastructure according to safer standards.
After the 1989 Loma Prieta earthquake, which caused extensive damage to several bridges in Northern California, many central and northeastern states began adopting new seismic provisions for highway bridges.
In New York, bridge owners hired seismologists to assess the risk of this hazard here. The Federal Highway Administration administers seismic retrofits of bridges through local authorities, under a 1991 inspection and rehabilitation program mandated by Congress. In 1998, the New York City Department of Transportation (DOT) developed Seismic Criteria Guidelines, which it updates as new science and solutions emerge.
New York City began seismic retrofitting of critical and essential bridges in 1998. Transportation agencies serving the New York area either have retrofitted or are in the process of retrofitting the bridges that they manage.
Seismic isolation is one of the more common methods of seismic protection in bridges and structures. In New York City, the JFK Light Rail system uses this method. This approach protects bridges or structures by isolating the earthquake movement from the foundation to the structures. Isolators (rubber and steel bearings) are mounted between the bridge deck and its piers, or between the building and its foundation. Isolators are intended to absorb the earthquake’s energy and minimize the energy transferred to the structure.
DOT is in the process of retrofitting the Brooklyn Bridge to conform to current seismic performance requirements outlined in the infrastructure codes. Under Contract 7, which began in September 2019 and is set to continue until 2023, the DOT is working to improve the load carrying capacity of the arch blocks, strengthen the masonry towers, and focus on repairs of the historic brick and granite components. This retrofit includes replacing the original timber piles with stronger structural piles and reinforcing the masonry elements of the bridge. Other bridges have been replaced where seismic performance was assessed as inadequate.
Seismic assessment of bridges in the New York City area requires evaluating each bridge for performance standards based on whether the bridge is determined to be critical, essential, or other. Retrofitting of older bridges or designs of new bridges should incorporate design elements that fit the level of damage expected from the projected earthquake and allow for repairs required after the event.
NYCDOT, which owns and maintains 799 bridges, is in the process of implementing seismic retrofits of all its critical, essential and other bridges.
Protecting Other Infrastructure
The New York City Department of Environmental Protection (DEP) currently conducts several projects to enhance seismic protection of the wastewater treatment system. DEP is retrofitting wastewater treatment facilities and methane gas storage systems to withstand earthquake activity, because most were designed and built prior to implementation of the current, more stringent seismic standards. To reduce the risks associated with seismic activity to New York City’s sewer system, DEP is inspecting and repairing structural deficiencies in some of the major sewers.
DEP is conducting a study to assess the seismic resiliency of our water supply system (water tunnels, piping, clean water pump stations, dams, shafts, and tanks) and to determine the appropriate seismic design standards. Study findings will prioritize areas in the water distribution system requiring retrofits to meet current seismic standards. City Water Tunnel 3 (described in the NYC Hazard Environment) is currently designed to strict seismic standards.
Applying the City’s seismic guidelines, the MTA, which is administered by New York State, is currently incorporating seismic requirements into its bridge and tunnel restoration projects within New York City.
Research and Professional Education
Collaboration among seismologists, geologists, engineers, architects, politicians, and emergency managers is required to manage earthquake risks. Further research into the potential impacts of earthquakes on New York City will expand knowledge about this hazard and promote greater public awareness.
Further research may include earthquake impact modeling of New York City’s unique built environment to estimate potential physical and economic losses, incorporating New York City’s large stock of older buildings, soil conditions, and unique geological characteristics. In July 2018, USGS produced a one-year probabilistic seismic hazard forecast for the central and eastern United States from induced and natural earthquakes.
The Next Generation of Ground-Motion Attenuation Models was a multi-disciplinary research endeavor that concluded in 2008. Involving collaboration from academia, industry, and government, this initiative focused on creating a consensus for new ground-motion prediction equations, hazard assessments, and site responses for the Central and Eastern North American region. This project marked a significant advancement in our understanding and prediction of ground motions, especially in the western United States. It replaced the earlier models from the 1990s and early 2000s, providing a more robust and reliable estimate of ground motions.
The Earthquake Engineering Research Institute established a New York–Northeast chapter to promote awareness of earthquake risk and to offer educational resources on how to reduce this risk at all levels. The organization relies on interdisciplinary expertise, drawing from the fields of engineering, geoscience, architecture, planning, and the social sciences.
The Multidisciplinary Center for Earthquake Engineering (MCEER), in collaboration with the Structural Engineering Association of New York, initiated studies to better understand the vulnerabilities of unreinforced masonry buildings in New York City. Working alongside the State University of New York at Buffalo, MCEER completed shake-table tests on prototypes of unreinforced masonry structures by 2015. This was a precursor to an extensive program aimed at devising engineered solutions for New York City’s archaic building stock.
Public Education and Outreach
Many New Yorkers are unaware that their community is at risk to seismic danger from earthquakes. Because earthquakes occur unexpectedly, New Yorkers will not have advanced warning that one will strike, so promoting awareness and preparedness among local communities is essential.
NYC Emergency Management (NYCEM)’s Ready New York campaign encourages New Yorkers to be prepared for all types of emergencies, to develop a personal disaster plan, and to stay informed about the entire range of hazards that may affect the City. NYCEM’s Ready New York Preparing for Emergencies in New York City guide explains what to do when an earthquake strikes and the steps to take immediately after.
NYCEM’s Ready New York Reduce Your Risk Guide includes long-term strategies for homeowners and residents to reduce the potential damage that an earthquake can cause.
Additionally, NYCEM’s Strengthening Communities program offers grants to community networks to build their emergency preparedness plan and support local community resources. The training program focuses on five key areas/deliverables to build an emergency plan specific to your community: Creating a needs assessment; Designing community maps of the area where you provide services; Building a resource directory; Preparing a communication strategy; Creating donations and volunteer management plans. NYCEM staff provide training, coaching sessions, and tools that guide participating networks through the program.
Earthquakes can inflict psychological harm in addition to physical harm, so it is essential to plan for mental health services as part of any future response and recovery effort. The New York City Department of Health and Mental Hygiene’s Mental Health First Aid education program alerts the public to the range of potential mental health issues, how to identify warning signs, how problems are manifested, and the types of commonly available treatments.
FEMA and the Northeast States Emergency Consortium organize annual Great Northeast Shakeout drills to encourage organizations, households, and agencies to practice safety during an earthquake. These drills are an opportunity for groups to update their preparedness plans, restock supplies, and secure items in their homes and workplaces to prevent damage and injuries if disaster strikes.