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 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 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
Wood	12,400	1,600	90	0	14,100	42%
Steel	1,200	400	40	0	1,640	5%
Reinforced Masonry (RM)	900	500	80	0	1,480	4%
Unreinforced Masonry (URM)	9,400	4,300	800	100	14,600	44%
Other	1,000	350	40	0	1,390	4%
Total	24,900	7,150	1,050	100	33,200	100%

Source:  NYCEM, HAZUS, and Department of Finance 2018.

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)
5.2	4,672.00	77.00	4,749.00	66*	1,800	130	100	493,000

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)
100-year	$0.1	$0.1	$0.2	0	0	0	0.2
500-year	$6.1	$2.0	$8.1	28	575	50	3.1
2,500-year	$64.3	$20.4	$84.8	1,430	84,626	900	34.0
Annualized Losses	$0.1	$0.1	$0.2	N/A	N/A	N/A	N/A

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.