Monday, July 16, 2012
Negative quake?
Was awakened early this morning by a big THUMP.
Sounds that wake you are not completely heard; sometimes you can mentally 'replay' the sound to get more detail, but usually not. With that limitation, the sound reminded me of three possible sources: a car crash, a falling tree, or a small earthquake. A car crash of that intensity would bring sirens and other activity, but I didn't hear any of that afterward. There's no wind tonight, and tree-cutters aren't usually active at 2 AM, so a falling tree is unlikely. Earthquake is thus the least unlikely of those three known sounds.
I looked at the NW Seismic Network webpage to see if any quake is on the map yet. No, but they don't record small quakes immediately, so I need to check later.
However: the webpage showed something more interesting than a minor quake.
A negative magnitude.
I'm sure it's a computer glitch, but it made me think. What would a negative magnitude mean? Well, the Richter scale is part math and part subjective, so we can't say for sure. If it were pure math, a negative magnitude would mean a time of unusual stillness. Specifically, a "-0.5 quake" would represent a moment when the earth's movement was only 32% of its typical baseline wiggling.
The formula would be:
Actual amplitude = 10^(-0.5) * Baseline amplitude.
= = = = =
Later: the NW Seismic map was updated, but no quakes anywhere around here, not even the negative kind. Maybe the Thump was a car hitting something after all. ¶ 3:29 AM
Sounds that wake you are not completely heard; sometimes you can mentally 'replay' the sound to get more detail, but usually not. With that limitation, the sound reminded me of three possible sources: a car crash, a falling tree, or a small earthquake. A car crash of that intensity would bring sirens and other activity, but I didn't hear any of that afterward. There's no wind tonight, and tree-cutters aren't usually active at 2 AM, so a falling tree is unlikely. Earthquake is thus the least unlikely of those three known sounds.
I looked at the NW Seismic Network webpage to see if any quake is on the map yet. No, but they don't record small quakes immediately, so I need to check later.
However: the webpage showed something more interesting than a minor quake.
A negative magnitude.
I'm sure it's a computer glitch, but it made me think. What would a negative magnitude mean? Well, the Richter scale is part math and part subjective, so we can't say for sure. If it were pure math, a negative magnitude would mean a time of unusual stillness. Specifically, a "-0.5 quake" would represent a moment when the earth's movement was only 32% of its typical baseline wiggling.
The formula would be:
Actual amplitude = 10^(-0.5) * Baseline amplitude.
= = = = =
Later: the NW Seismic map was updated, but no quakes anywhere around here, not even the negative kind. Maybe the Thump was a car hitting something after all. ¶ 3:29 AM
