Posted on 04/23/2020 6:56:51 AM PDT by BenLurkin
The new research provides the first quantitative synthesis of faulting across the entire continent, as well as hundreds of measurements of compressive stress directions—the direction from which the greatest pressure occurs in the Earth's crust. The map was produced by compiling new and previously published measurements from boreholes as well as inferences about kinds or "styles" of faults based on earthquakes that have occurred in the past.
The three possible styles of faulting include extensional, or normal faulting, in which the crust extends horizontally; strike-slip faulting, in which the Earth slides past itself, like in the San Andreas fault; and reverse, or thrust, faulting in which the Earth moves over itself. Each one causes very different shaking from a hazard point of view.
In addition to presenting a continent-level view of the processes governing the North American plate, the data—which incorporates nearly 2,000 stress orientations, 300 of which are new to this study—offer regional clues about the behavior of the subsurface.
In the Eastern U.S., for example, the style of faulting revealed by the study is exactly the opposite of what would be expected as the surface slowly "rebounds" following the melting of the ice sheets that covered most of Canada and the northern U.S. some 20,000 years ago, according to Lund Snee. The discovery that the rebound stresses are much less than those already stored in the crust from plate tectonics will advance scientists' understanding of the earthquake potential in that area.
In the Western U.S., the researchers were surprised to see changes in stress types and orientations over short distances, with major rotations occurring over only tens of miles—a feature that current models of Earth dynamics do not reveal.
(Excerpt) Read more at phys.org ...
Boston.
There was a small quake in the gulf of Mexico awhile back. My mom felt it in Ocala.
I agree, the color bar on that grid needs to be inverted, Cali should be red, east coast green.
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