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Another small quake 413 miles away

A project log for Device for Seismic Noise Analysis

A device that monitors the statistics of the magnitude and the 3-D direction of seismic noise might detect earthquakes before they happen.

michael d. 6 days ago0 Comments

A minor earthquake occurred on Wed Sep 13, 2017 at about 12:33:10 CDT (Sep 13, 2017 17:33:10 UTC) 11.43 km northeast of Peterstown, WV. The magnitude was 3.1.

Our main machine recorded this event 23 seconds later. The vector magnitude plot for that hour  is:

The brief event early in the hour appears to be something very local. It showed up the local USGS affiliated "strong motion" machine 7 miles or so away even though the West Virginia event did not show up well (see below). Here is an isolated view of the vector magnitude data from the West Virginia event:

There appears to be no advance vibration from this distant event whatsoever.  Here is the combined probability statistic data from the entire hour.

This shows a substantial deviation from normal statistics for about 1000 seconds after the main front of the West Virginia tremor, a hint of which can be seen in the actual vector magnitude data. I speculate that the deviation from normal statistics may be due to echoes from the nearby Smoky mountains to our South and from the Appalachian mountains farther away to the East. 

This graph shows the horizontal location in radians of the data points for the hour, indicating a persistent Eastward trend in  the average location of the noise for about 1000 seconds:

Here is the data from the Knoxville USGS machine, by way of comparison. It records (in black) the event early in the hour that showed up on my machine, but there is only the barest hint of the West Virginia event at 1:33 PM EST. Here is the data from all of this afternoon on that machine:

Here is a cutout view of this data showing the local early event (in black) and the barely perceptible West Virginia event. I added the time labels.

The take home message that seems to be evolving is that distant events are not associated with detectable anomalies of the noise before the event, but local events do seem to be associated with anomalies. More data points (and lots of them!) are needed.

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