Earthquake Preparedness Month — February 2026

As part of our commitment to keeping LaSalle County residents safe and informed, February is designated Earthquake Preparedness Month. While earthquakes are less frequent here than in parts of the western United States, our county and region are not free from seismic risk. Understanding that risk, recognizing local geology, and knowing what to do before, during, and after an earthquake can save lives and reduce damage.

LaSalle County’s Seismic Context

LaSalle County sits atop a landscape shaped by ancient geological forces. While Illinois does not sit on a major active plate boundary like those in the western U.S., the region contains ancient fault and fold structures that can influence seismic activity.

🔹 Sandwich Fault Zone Northern Illinois is home to the Sandwich Fault Zone, a broad system of ancient faults that trends roughly northwest from Oswego through DeKalb and into Ogle County — and it intersects parts of LaSalle County’s northern neighboring region. Although it is generally not highly active in modern times, small earthquakes have been recorded along or near this structure, such as a 3.4-magnitude event near Somonauk in July 2024, likely associated with movement on this old fault system.

🔹 Peru Monocline & LaSalle Anticlinorium Another significant subsurface feature is the Peru Monocline, which extends southeast from Dixon across western portions of LaSalle County. This fold is part of the larger LaSalle Anticlinorium, representing ancient crustal deformation. Evidence shows seismicity in the vicinity of this structure, including a 4.2-magnitude event northwest of Ottawa in 2004.

🔹 Regional Seismic Zones Impacting Illinois Beyond local geologic structures, LaSalle County is also influenced by larger seismic zones that lie to the south and southeast:

• The New Madrid Seismic Zone (NMSZ) — historically responsible for significant earthquakes in the central U.S. (1811–1812) — still poses a long-term risk to Illinois.

• The Wabash Valley Seismic Zone (WVSZ) — along the Illinois-Indiana border — is another source of moderate earthquakes that can propagate shaking into northern and central Illinois areas.

These geological features, though ancient and often dormant, underscore the importance of understanding local seismic risk — even in regions like LaSalle County where earthquakes are infrequent.

Documented Earthquakes in the Past 25 Years

Though strong earthquakes are rare here, LaSalle County and nearby areas have experienced measurable seismic activity:

June 28, 2004 — Magnitude 4.2A seismic event about 8 miles northwest of Ottawa produced noticeable shaking across multiple states.

November 15, 2023 — Magnitude 3.6 (nearby)An early-morning earthquake centered near Standard in neighboring Putnam County was felt in LaSalle County.

Historical Regional Activity Records also show earthquakes of various magnitudes in northern Illinois and surrounding areas — including events in the late 1990s and early 2000s — reminding us that seismic activity, while infrequent, does occur.

What the Science Tells Us

Illinois lies within the central United States seismic belt and is influenced by intraplate stresses. • The probability of a magnitude 6.0 or greater earthquake in major Midwest seismic zones (over 50 years) is significant. • While most events are small and go unnoticed, the underlying geology can transmit shaking over larger distances than in many western states.

How to Prepare This Earthquake Preparedness Month

Here are key steps every household and business should take:

🔹 Secure Your Space

• Anchor heavy furniture

• Secure water heaters and appliances

🔹 Plan & Communicate

• Develop a family emergency plan

• Know safe spots in each room (e.g., sturdy tables)

🔹 Build an Emergency Kit Include essentials — water, food, flashlight, first aid, meds, and important documents.

🔹 Practice “Drop, Cover, Hold On” During shaking, drop to the ground, take cover under sturdy furniture, and hold on until the shaking stops.

Stay Informed — Stay Prepared

Earthquake preparedness isn’t about fear — it’s about readiness. Take this month to educate your family, update your emergency plans, and strengthen your home against seismic hazards. The LaSalle County Emergency Management Agency is here to support you with resources and guidance including our website www.lasallecountyema.org and smart phone application available in your Google or Apple App Store.

Stay safe, LaSalle County!

Fred Moore

Director

LaSalle County EMA