💧🌏 Greg Cocks: "Earthquake Focal Mechanisms – …" - TechHub

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Greg Cocks @GregCocks@techhub.social

Earthquake Focal Mechanisms – Life’s A Beach(Ball) [USGS]
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https://www.usgs.gov/observatories/yvo/news/earthquake-focal-mechanisms-lifes-a-beachball <-- shared technical link
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https://doi.org/10.1029/2003JB002675 <-- shared paper
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#geology #faulting #risk #hazard #spatialanalysis #spatial #GIS #mapping #earthquake #beachball #beachballdiagram #slip #orientation #slipdirection #focalmechanism #focalsphere #structuralgeology #seismic #waves #compression #tension #mechanism #geomorphometry
@USGS

schematic - earthquake focal mechanisms

photo - rock slide after Hebgen Lake Earthquake

graphics and charts - Focal mechanism determined by moment tensor analysis, which uses a model to fit the long-period (~10 s period or greater) ground motion records recorded at multiple locations. This example is for a M4.4 event that occurred during the 2017 Maple Creek earthquake swarm. Left-hand plots show the fit between recorded ground motions at different seismic stations (black lines) and modeled ground motions (red dashed lines). The associated focal mechanism beachball diagram is shown at the right, with labels showing the directions to stations used in the model. Above the mechanism, various parameters of the model solution are listed. Depth indicates the earthquake depth. Strike indicates the horizontal directions of the two possible fault planes. Rake indicates the angle of modeled slip on those fault planes. Dip indicates the steepness angle of the fault plane from vertical. M0 indicates seismic moment of different components of the mechanism. Mw indicates moment magnitude. Percent DC is the percentage of the modeled source that represents simple faulting, while CLVD and ISO indicate deviations from simple faulting. Variance, Var. Red., and RES/Pdc indicate parameters associated with how well the model explains the data.

beach ball plots - Left hand plot shows a focal mechanism from an earthquake where the fault is horizontal (red line), and the motion is right-lateral strike skip. The initial direction of wave motion (either back toward the source or away from the source is shown by the arrows. Right hand plot shows the associated beachball diagram, with compressional (“C”) and tensional (“T”) quadrants labeled. (Source, wikipedia.com, By Mikenorton - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4050363)

Oct 21, 2024, 10:20 PM··Web

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