The Friday Intel | 03.14.26: What's Underneath Westchester — The Seismic Data Nobody Talks About

Tuesday's magnitude 2.3 earthquake in Sleepy Hollow was small. But the seismic data underneath Westchester County tells a much bigger story — about a 185-mile fault system, a previously unknown seismic zone discovered less than a mile from Indian Point, and buildings that were never designed to handle what the geology says is coming.

In This Episode:
(0:00) Cold Open — Your house shook. Here's the question nobody's asking.
(0:30) Intro — Why the data behind Tuesday's quake matters
(1:30) The Data — Ramapo Fault, Dobbs Ferry Fault, and Columbia's 2008 discovery
(3:30) The Surprise — New York's 70-year gap in seismic building codes
(5:00) What This Means for You — Property risk, insurance, and Indian Point
(6:00) Close

Sources:
USGS Earthquake Hazards Program — https://earthquake.usgs.gov
Columbia University Lamont-Doherty Earth Observatory — https://lamont.columbia.edu
FEMA Unreinforced Masonry Guidelines — https://mitigation.eeri.org
Nuclear Regulatory Commission — https://www.nrc.gov

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Transcript

SPEAKER_00 0:01

On Tuesday morning, your house shook. A 2.3 magnitude earthquake hit Sleepy Hollow, and 1,200 people reported it to the USGS. Most of us moved on. But what if I told you Westchester County sits on one of the most active fault systems in the northeastern United States, and that Columbia University scientists estimate a magnitude 5 earthquake hits this area once every hundred years. This is the Friday Intel. Let's go deeper. Welcome to the Friday Intel from I Live Here Westchester. Every Friday we go deeper on one data story that affects your life in Westchester County. This week, earthquakes. Specifically, the seismic data beneath your feet that most residents have never thought about. Tuesday's quake was small, no damage, no injuries. But the data behind that event tells a much bigger story about fault lines, building vulnerability, and a nuclear plant the NRC once ranked as having the highest earthquake risk of any reactor in the country. Here are the numbers. Over the past 56 years, the USGS has recorded an average of 2.8 earthquakes per year in or near Westchester County, most you never felt. But roughly once every eight years, one hits magnitude three or higher, strong enough to rattle windows and send dishes across countertops. The fault driving this is the Ramapo Fault, 185 miles long. It runs from Pennsylvania through New Jersey and terminates here in Westchester. It is the most seismically active fault corridor in the northeastern United States. Closer to home, the Dobbs Ferry Fault runs along the eastern Hudson through Westchester. In 1985, a magnitude four earthquake struck Ardsley, felt in Philadelphia and southern Canada. That event upgraded it from a fracture zone to a full fault classification. Then in 2008, Columbia's Lamont Doherty Earth Observatory discovered a previously unknown seismic zone running 25 miles from Stanford, Connecticut to Peakskill, New York. It intersects the Ramapo Fault and passes less than one mile north of Indian Point. Based on that discovery, they estimated a magnitude five earthquake occurs here on average once every hundred years and a magnitude six once every six hundred seventy years. Here is what caught me off guard. New York did not adopt seismic building codes until 1995. California started in 1925. That is a 70 year gap. And while modern buildings now meet stringent standards, the vast majority of buildings in Westchester were built before those codes existed. The specific vulnerability is unreinforced masonry, brick and stone buildings where walls are not secured to roofs and floors. According to FEMA, these account for 75% of all building losses in a magnitude 7 earthquake. Think about the pre-war brick buildings lining Terrytown, Dobbs Ferry, White Plains, Yonkers, and Peakskill. None were built with earthquake resistance in mind, and here is the kicker. East Coast earthquakes travel four to five times farther than west coast earthquakes of the same magnitude. Our bedrock is older, harder, denser. It conducts seismic energy like a bell. So what does this mean if you live here? Tuesday's earthquake was not unusual. 2.8 per year is the baseline. The risk of a larger event, magnitude five or above, is real, not imminent. But statistically, it is when, not if. Columbia's data says once every hundred years. The last event in that range was 1884. Do the math. If you own property here, particularly older brick or stone, it is worth understanding what unreinforced masonry means for your exposure. FEMA has retrofit guidelines. Your insurance may or may not cover earthquake damage. An Indian point may be closed, but spent fuel is still on site. The NRC kept it in the highest category of seismic evaluation for a reason. That is your Friday intel. The ground under Westchester is more active than most people think. The buildings on top of it are more vulnerable than most people realize. If this was useful, share it with someone who lives here. I will see you Monday on the Westchester brief. I am Jim, and I live here.