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Jul 14 • 10 tweets • 9 min read
Ok Oregon, you asked so we’re answering your #QuakeQuestions from Monday. If you’re not already following @OregonOEM or @PNSN1 be sure to do so as they are your go-to's for local info about emergencies and earthquakes in Oregon and the Pacific Northwest.
What’s the deal with earthquakes in Oregon? As many of you mentioned in Monday's #QuakeQuestions post, this region of the U.S. is capable of hosting very large (M9!) earthquakes along the #Cascadia subduction zone where the Pacific plate slides beneath the North American plate. Cascadia megathrust fault map. Topo-bathymetric map of the CSubduction zone schematic. Schematic cross-section of the ac
How do we know such large earthquakes are possible? Check out this thread to learn more about the 1700 M9 Cascadia earthquake – the largest known earthquake to have occurred in the conterminous U.S.
The @USGS has developed earthquake scenarios to simulate how an M9 earthquake would shake the Pacific Northwest in modern times. These scenarios help us examine the exposure of structures, lifelines, utilities, & transportation corridors to potential earthquakes. Scenario earthquake for a M9.0 along the Cascadia subduction
Speaking of structures, though @USGS doesn’t implement building codes or retrofits, our science and hazards maps ARE used to inform these types of preventive measures that help protect people and infrastructure from the hazards of earthquake shaking. usgs.gov/programs/earth… Earthquake hazard map showing peak ground accelerations havi
According to @OregonOEM, the two most common types of retrofitting are bolting the house (mudsill) to the foundation and reinforcing the cripple walls (aka “pony” walls) with plywood sheathing. oregon.gov/CCB/homeowner/… Image from @OregonOEM showing a diagram of a house to help e
.@FEMA and @Readygov's QuakeSmart program can also help businesses identify and address their seismic risks through retrofitting and other earthquake mitigation activities.
fema.gov/emergency-mana…

ready.gov/sites/default/…
Tsunamis are possible along the OR (& entire U.S. west) coast from earthquakes near & far. Tsunami messages are issued by Tsunami Warning Centers like @NWS_NTWC & may come through outdoor sirens, local officials, text message alerts & phone notifications. ow.ly/u1Ow50JWiQb Diagram of what to do if you are near the coast and feel a l
#DYK OR, CA & WA, are now powered by the @USGS_ShakeAlert earthquake early warning system? With ShakeAlert you can receive messages about EQ shaking on your phone before it arrives at your location, giving you time to drop, cover, and hold on. Learn more: ow.ly/6k2y50JWiYv ShakeAlert Is Not Earthquake Prediction. Cartoon showing tha
Thanks to @NWSPortland for retweeting our #QuakeQuestions tweet on Monday! We plan on answering more questions over the next couple weeks. Want more info on OR earthquakes, tsunamis & preparedness? Visit the @OregonOEM hazards & preparedness page ow.ly/475m50JWj42

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More from @USGS_Quakes

USGS Earthquakes Profile picture
Jan 26
Today marks the 322nd anniversary of the 1700 AD Cascadia earthquake – the largest known earthquake to have occurred in the "lower 48" United States.
This (estimated) magnitude 8-9 earthquake ruptured along the 1300-km-long Cascadia subduction zone which sits off the coast of northern California, Oregon and Washington. Topo-bathymetric map of the Cascadia subduction zone. Cascad
Here, the eastern margins and dense oceanic crust of the Gorda and Juan De Fuca plates meet their demise as they subduct beneath the lighter continental crust of the north American plate. Cross-section or side view schematic of the Cascadia Subduct
Read 9 tweets
USGS Earthquakes Profile picture
Oct 14, 2021
An intro to earthquake prediction 🧵🧵

Individual earthquakes can’t be usefully predicted. It’s not because they’re mystical or magical. Earthquakes obey very simple physics. The issue is that earthquakes occur deep underground.
In California, earthquakes typically rupture faults at depths of ~10 mi (~15 km). We have no eyes on the fault at depth: can’t see what materials are in the fault, where they’re lubricated by fluids, how close any point is to failure, or how large an area might fail.
If you can’t see the fault at depth, you can’t directly predict what the fault will do. Instead some researchers try to correlate large quakes with other things like having small quakes – or maybe not having small quakes? It’s not clear that there is any predictive power here.
Read 6 tweets
USGS Earthquakes Profile picture
Sep 1, 2021
**New publication alert**
What could happen to communication networks if a large #earthquake happened in the SF Bay Area, along the Hayward fault? 📞📱☎️📳
The new #HayWiredScenario chapter on telecommunications & ICT asks “what if” & explains why we should #TextNotTalk Map depicting SCENARIO distribution of shaking severity in a
Using proxies including power shutoffs, wildfires, & other earthquakes to model what happens to #telecom in a #HayWiredScenario, they found vulnerabilities in power service, cell sites on buildings and poles, and data lines crossing the fault surface rupture. Map of the San Francisco Bay region, California, showing fib
Contributing to the issue are multiple competitive service providers in a largely unregulated industry, convergence of analog and digital systems, layers of hardware and software functionality, dependence on electric power, and the rapid evolution of technology. Photo showing co-located electrical and telecom infrastructuThese photos show repair dependence between telecommunicatio
Read 9 tweets
USGS Earthquakes Profile picture
Jul 9, 2021
Yesterday afternoon, just before 4 pm local time, a M6.0 earthquake occurred at the California-Nevada border. Let’s dive deeper into some of the regional geology on this edition of #FaultFriday.
East of the San Andreas fault, the plate boundary doesn’t stop moving. Even though ~70% of the relative motion of the Pacific-North American plates occurs within the San Andreas fault system, that leaves ~30% to be accommodated elsewhere.
Moving east from the San Andreas fault from ~San Francisco, more plate motion is accommodated at the eastern rangefront of the Sierra Nevada. If you’ve ever wondered why the Sierra look even more impressive from the east than the west, enter: active tectonics.
Read 13 tweets
USGS Earthquakes Profile picture
Jul 9, 2021
Update on the M 6.0 #earthquake that occurred at 3:29 pm Pacific Time July 8, in Antelope Valley, California, near the Nevada border. #califearthquake You can find up-to-date details about the earthquake here: earthquake.usgs.gov/earthquakes/ev…
Shaking of intensities up to VII was reported nearest the epicenter. The quake was felt all the way to the Pacific Coast and throughout CA’s Central Valley as well as strongly in Reno and Carson City.
Did You Feel It? Report here:
earthquake.usgs.gov/earthquakes/ev…
Our @USGS_ShakeAlert earthquake early warning system sent out some ShakeAlert-powered alerts through phone apps and @Google @Android. Check out earthquake.usgs.gov/earthquakes/ev… for more information about ShakeAlert’s performance.
Read 5 tweets
USGS Earthquakes Profile picture
Jul 6, 2021
An M5.2 earthquake occurred 12 km (7.5 mi) NNW of Kukuihaele, Hawaii yesterday at 1:34 PM local time. So far >1,300 people have reported feeling shaking. If you felt this quake (or not!), click the link below to tell us about your experience. For more on EQs in Hawaii, see 🧵👇.
Thousands of earthquakes occur every year in the State of Hawaii most of which are small & caused by eruptive processes w/in the active volcanoes on & around the Island of Hawaii, especially in the southern districts where the Kilauea, Mauna Loa & Loihi volcanoes are most active. Image
Other EQs can occur in Hawaii along tectonic faults in the crust & upper mantle & can be related to deep structural adjustments from the weight of the lava-built islands on Earth's underlying crust. This is the most common source of damaging EQs north of the Island of Hawaii. Image
Read 7 tweets

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