Yes, swarms aside, it is still Friday, and on this channel, that means #FaultFriday. To learn more about the area around the Westmorland swarm, let’s look at the Imperial fault of southern California today.
The Imperial fault is a right-lateral strike-slip fault (ow.ly/gKEq50BIfDq) that runs south of the Salton Sea, across the US-Mexico border, and into Mexico. The Imperial fault had two significant earthquakes in the 20th century, a M6.9 in 1940 and a M6.5 in 1979. Map showing Imperial fault and Westmorland Swarm in southern
Before the 1940 El Centro event, this fault probably did not have an earthquake in the previous 300 years. Geologists can literally uncover the history of past earthquakes along a fault by digging a shallow trench across a fault and observing and dating the offset layers.
The Imperial fault is part of the San Andreas fault system and overall Pacific-North America plate boundary. The Imperial fault transfers slip from the spreading occurring in the Gulf of Mexico and plate boundary faults in Mexico onto the San Andreas system.
The Westmorland swarm has been occurring to the north of the Imperial fault. This swarm is rupturing in an area typical of swarms, perhaps because of thin crust here and high heat flow given the seafloor spreading in the Gulf of California.
Here is a scenario event (this event has not occurred!) for shaking that could result from an M7 event on the Imperial fault. MMI>VII is expected close to the fault. Weak to light shaking would be expected >100 km from the epicenter. --🐋 Scenario Shakemap of hypothetical event on the Imperial faul

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More from @USGS_Quakes

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
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
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
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
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
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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