Originally posted by Violater1
Originally posted by ns9504
reply to post by Violater1
Magnitude, type, depth, and location need to be factored in before sweeping statements are made. Yes, the numbers are higher than last year,
but 3K in the world of earthquakes is really not that big.
Respectfully, this thread feels like its trying to make mountains out of mole hills...
Please read the tables that I provided as well as the links before posting.
This is about earthquakes in the USA not world. If you read the facts, it's quite clear.
3000 additional earthquakes in the USA is something not to shake a stick at.
I did read the facts, for the USA and the world. I'm not confused. I still think you are taking the information and putting in to your own context.
However, I e-mailed my dad (50 years with the USGS as a seismologist) and asked him why more earthquakes in 2010 in the US. This is his response:
"It's unfortunate that the USGS doesn't explain the apparent increase in earthquakes in the US over the past decade.
Note, however, the increase in recorded earthquakes is not the same proportionally across all magnitudes. Proportionally, the number of M 7 to 7.9
quakes changed not at all over the decade. These are the most powerful & therefore the most destructive earthquakes. M 6 to 6.9 quakes showed a lot of
variation in number w/ an apparent uptick toward the end of the decade. These quakes are felt over wide areas. It's very unlikely that any M 6 to 7.9
quakes in the US have gone unrecorded in the US in at least the last 50 years. So to look for periodicity or episodicity one should look at least 50
years of available data.
On the other hand, there has been a significant increase in M 2 to 3.9 earthquakes throughout the decade and what looks like significantly more in
2010. M 2 & 3 quakes release too little energy to be felt by humans in all but the most quiet surroundings. The increase in energy release by these
small is not much compared to a single M 7 quake. Each increase in magnitude by one equals the release of 32 times as much energy. A M 7 quakes
releases 32 x 32 x 32 x 32 32 as much energy as a M 2 quake.
However, I can think of three reasons to explain the distribution of quakes across the decade & magnitude scale.
1. More sensitive instruments to detect earthquakes & greater density of instruments across the US. Over the last decade USGS has largely replaced
analog seismometers with more sensitive digital seismometers This would explain much of the increase in M 2-3 quakes. Any old seismometer can detect a
M 6 or 7 quake, but a really sensitive one is needed to detect M 2 & 3s.
2 Earthquakes are not evenly distributed over time. They happen more frequently at some times than at others. Just as with tossing coins. The
probability of getting a head on any toss is always 0.5, but still there is a significant probability of tossing heads two times in a row. Or even
getting a head four times in a row. Looking at the last 50 or so years of M 6 to 7.9 quakes would give a much better idea if how the amount of energy
released over time has changed.
3. There is a real variation in the number of earthquakes over time. I remember reading that the number of small quakes in southern California between
Palm Springs & the Gulf of California has increased in the last few years, but its the big ones we watch for."
Take or leave it. I believe and trust my dad, the scientist.
