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3-D view of earthquakes in the New Madrid Seismic


3-D view of earthquakes in the New Madrid Seismic Zone

Data on thousands of earthquakes in the New Madrid Seismic Zone since 1974 is available from the Center for Earthquake Research and Information at the University of Memphis. Most of those were too small to feel. But they’re real interested in that zone at Memphis because they’re awfully close to it, and it has unleashed some monster quakes in the past.

The data includes the estimated depth of the quakes as well as the geographic coordinates. Below is my first effort to use that data to visualize the fault zone in 3 dimensions. There is a lot of data that gets in its own way, so an animation that tilts and rotates was chosen as a a means to see it from different angles.

Depth data

Did you notice that there seems to be a plateau of sorts in the data at exactly 5 km? That’s suspicious. Likewise the lighter grouping at 10 km. I can take a bucket of data and manipulate it into a visualization. But I’m afraid that I don’t know enough about this particular data, how it is collected, and what issues there are in its accuracy and reliability. The page titled Description of Catalog Data doesn’t help much in that regard, but it does make me think I should comb the data I’m using for zero depths.

So, as interesting and useful as this looks, I don’t think I’m going anywhere with it until I know why the data bunches up at those two depths. If anyone comes across this who can tell me how to cull potentially unreliable entries from the dataset, I’d love to hear from you.

If that data is true, then those groupings at 5 and 10 km depths would be very interesting, indeed.

Update: Here is a histogram of depths rounded to the nearest kilometer. Remove data at zero, 5, and 10, and the smoothing curve will be even lower than shown.

Historgram of depths of 8,557 central US quakes to nearest 0.1 kilometer

Historgram of depths of 8,557 central US quakes to nearest 0.1 kilometer

Update #2: The curator of this data kindly responded to a query, and he reports that the USGS normally fixes the depth at 5 km in order to get a more accurate epicenter and origin time. The data is from a variety of sources, though, and that’s why it doesn’t all describe a level plain right at 5 km.

He also states that the USGS sometimes fixes the depth of events at 10 km, but normally not in this part of the country. This second histogram rounds all depths to 0.1 km. There is an obvious spike at exactly 10.0 that certainly suggests artificial coersion of some class of data; if it were due to actual activity at around 10 km, it would more likely create a hump in the histogram including 9.8, 9.9, 10.1, 10.2, etc.

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