What-if impact desk · inland

St. Louis / New Madrid — hypothetical M8

A plain-English scenario brief for a great earthquake centered in the New Madrid Seismic Zone (NMSZ), asking how strong shaking could play out across St. Louis metro and Mid-South / Midwest river cities — for education only.

Assumptions (read these first)

Scenario assumes a hypothetical ~M8 rupture in the New Madrid Seismic Zone (illustrative epicenter near the historic NMSZ core, SE Missouri / adjacent states).
Grounding: USGS and partner educational materials note that the 1811–1812 NMSZ sequence produced widespread felt shaking across the Midcontinent; modern urban exposure is very different from 1812.
Intensity language uses Modified Mercalli (MMI) concepts — what people and buildings might experience — with honest uncertainty (“could,” “might,” “historically…”).
No tsunami: this is an inland continental scenario.
Attenuation note: Midcontinent crust can transmit shaking farther than typical West Coast crust for a similar magnitude — a reason NMSZ scenarios matter for distant metros — but exact intensity at any address requires a full ShakeMap-style model we are not inventing here.

Qualitative shake map

Illustrative distance rings · Esri dark gray basemap

Very strong (MMI VIII+ language) Strong (MMI VII language) Felt / moderate (MMI V–VI language) Assumed epicenter region

Rings are schematic distance envelopes for teaching — not contour science. Soft soils, basin effects, and building type can change local intensity dramatically.

Shake intensity desk

MMI VIII–IX+ Near / core NMSZ

Closest communities in the Bootheel and adjacent river lowlands could experience very strong to violent shaking in an M8-class scenario. Unreinforced masonry and older river-town stock are historically vulnerable themes in NMSZ education.

MMI VII–VIII Strong-shake metros

St. Louis and Memphis metros sit in the range where a great NMSZ event could produce strong, damaging shaking — especially on soft Mississippi embayment soils. Exact MMI at a neighborhood is not something this desk invents.

St. Louis, MO–IL Memphis, TN Paducah, KY Cairo, IL

MMI VI–VII Who might feel strong shake

Farther Mid-South and Midwest cities might still feel strong or damaging shaking depending on path and site effects. Historically, NMSZ shaking has been felt over a very large footprint relative to West Coast crust.

Little Rock Nashville Evansville Springfield, IL Jackson, MS

MMI V–VI Widespread felt

Much of the central U.S. could feel a great NMSZ event. Feeling an earthquake is not the same as building damage — intensity falls with distance and local geology.

Infrastructure & impact themes

Educational themes commonly discussed for Midcontinent / river-city exposure — not a damage forecast for any structure.

Bridges & river crossings Mississippi / Ohio corridor mobility; liquefaction themes on river sediments.

Unreinforced masonry Older brick and stone stock in Midwestern / Mid-South downtowns.

River cities & soft soils Embayment and floodplain soils can amplify shaking relative to rock sites.

Lifelines Pipelines, rail, power, and water systems spanning a wide felt region.

Tsunami

Not applicable (inland)

A New Madrid continental rupture does not generate an ocean tsunami. Local seiche or river-bank effects are sometimes discussed in extreme scenarios, but this desk does not model them. For Pacific / coastal tsunami guidance, see official sources — not this page.

Educational framing informed by USGS New Madrid Seismic Zone materials, ShakeMap / MMI concepts, and Midcontinent attenuation discussion. Official science: USGS NMSZ · ShakeMap. This page is Ring of Fire education — not an official USGS product.

Disclaimer: Hypothetical scenario for information and education. Not a prediction, not financial or insurance advice, and not life-safety guidance. For emergencies, follow official civil defense and USGS instructions.