Earthquakes aren’t frequent in Colorado, but the state has a history of moderate- to large-magnitude earthquakes. Map shows earthquakes (1882–2000), including an 1882 magnitude-6+ earthquake west of Fort Collins.

You can report shaking at the DYFI tile: earthquake.usgs.gov/earthquakes/...

This is a region of high seismic hazard due to large crustal faults that accommodate deformation associated with subduction of the Indian Plate beneath Eurasian (and Burma) Plate.

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Earthquakes in this region occur in the crust, on the subduction interface (between the subducting Juan de Fuca/Explorer and North American plates), and in the subducting plate. This was a crustal earthquake in the North American plate. At this location the subducting plate is about 60 km deep.

Earthquakes in this region are not frequent, but the historical record shows larger earthquakes with the potential to cause damage. USGS earthquake catalog searches at: earthquake.usgs.gov/earthquakes/...

Magnitude 3.9 earthquake in southern Maine this morning. This is an area of low but persistent seismicity, including large historical earthquakes. Shaking reported by more than 20k people at distances of several hundred miles from the epicenter, including responses from Boston, New York, and DC.

@plutokiller.com I assume this account us impersonating you.

Because this earthquake ruptured to the east, sites “in front” of the rupture experienced this effect, having higher ground motions (and different frequencies). We see some of this in the asymmetry of ground motions, with higher ground motions east of the fault. earthquake.usgs.gov/realtime/pro...

Whoa, something weird with me posting this URL. Reposting with alt text.

earthquake.usgs.gov/realtime/pro...

These same physics happen with seismic waves and cause a sort of seismic Doppler effect, known as the directivity effect. We see this effect in the ground motions—higher ground motions off the west of the fault and asymmetry of the contours of ground motion.

earthquake.usgs.gov/realtime/pro...

Finite fault solutions tell us a bit more about what happened in the fault during the rupture. These analyses are only done for larger earthquake about M7+ for USGS. The model shows where the earthquake started (hypocenter) and where slip occurred on the fault.

Knowing when and how frequently large earthquakes have occurred is part of earthquake hazard assessment. Many events pre-date written records so geologists look for evidence in the geologic record, like this sand layer deposited by the tsunami from the last interplate Cascadia earthquake...

I was in coastal Oregon for part of the Thanksgiving holiday. Always a good reminder to think about what to do in the event of an earthquake and resulting tsunami. If you feel strong or long-duration shaking at the coast, make your way to high ground, following evacuation routes if they exist.

South of Juneau, July 2021

Not too many earthquakes where I live in Colorado, but I‘ve felt earthquakes while traveling in Alaska, Oklahoma, and Japan. I’m participating in #GreatShakeOut because knowing what to do in an earthquake is important for anyone who lives or travels to seismically active places.

The Midland area has seen moderate seismicity since at least 2015. Plots shows locations of M4.5+ earthquakes since 2015 overlying the long-term hazard estimates, which indicate relative low historical rates of seismicity.

Great post on Threads from Yann LeCun (who isn’t on bsky) about managing scientists.

Magnitude-3.7 earthquake near Pierre, South Dakota this afternoon. This is an area with infrequent seismic activity - only a few events occurring near today's epicenter in the past 40 years.

If you felt this earthquake, report it to the US Geological Survey:
earthquake.usgs.gov/earthquakes/...

Widely felt East Coast earthquake this morning. New Jersey epicenter, magnitude 4.8 (M4.8). This earthquake occurred in an area with previous historical seismicity but with low historical seismicity rates. Moderate-intensity shaking near epicenter, and light shaking felt more than 500 miles away.