Ever wonder what #EarthquakeHazard looks like for the entire US? The @USGS’s National Seismic Hazard Map (NSHM) defines the potential for earthquake ground shaking for various probability levels across the country.
The NSHM represents an assessment of the best available science in earthquake hazards and incorporates new findings on earthquake ground shaking, seismicity, slip-rates, frequencies of various magnitudes and long-period amplification over deep sedimentary basins.
Periodic revisions of these maps incorporate results of new research. The above, 2018 map is based on the most recent USGS models for the conterminous U.S. (2018), Hawaii (1998), and Alaska (2007).
Previous NSHM’s were developed in 1996, 2002, 2008, and 2014 and a 2023 update is on its way!
These maps provide information essential to creating and updating the seismic design provisions of building codes, insurance rates risk assessments, and other public policy used in the United States and can also help people assess the hazard to their homes or places of work.
Buildings, bridges, highways, and utilities built to meet modern seismic design provisions are better able to withstand earthquakes, not only saving lives but also enabling critical activities to continue with less disruption.
Many folks (and their kids) asked why earthquakes happen in the central and eastern U.S., far away from plate boundaries. There are many reasons! #QuakeQuestions🧵
First, the plate boundary is a lot wider than you might think. In California, most motion between the Pacific and North America plates happens on the San Andreas fault. But that plate motion is stretching the crust (and causing earthquakes) as far east as the Colorado Plateau.
In the past, the tectonic plates were very different than they are today. Remnants of ancient plates and past mountain building have left faults throughout the U.S. on which earthquakes can occur to relieve stress. And there are plenty of non-tectonic stress sources.
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.
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.
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.
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.
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.
**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
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.
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.
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.