Experts reject rain-earthquake link

[snopes]

The local weather bureau has used its emergency weather information system to dismiss rumors that the torrential rain falling on Zhanjiang would cause an earthquake.

http://www.chinadaily.com.cn/china/2...nt_6025071.htm

[Silas Sparkhammer]

It isn't wholly nonsense: whenever a major dam is completed and water begins to fill the reservoir, seismographs will record a swarm of "microquakes," as the earth balances the changing stresses. My old geology prof. called this "isostasy."

However, there is, to date, no link between this and any major earthquake.

Silas

(A bit of math: the Glen Canyon Dam has a volume of 27,000,000 acre feet; this is the same volume as one inch of rainfall over a circular area 400 miles in radius. A major dam, however, takes weeks or months to fill, whereas an inch of rain can fall over a very wide area in as little as a single day.)

[Hans Off]

What on gods earth is an "acre feet"?

That's the first time I have heard that unit of measurement!

Hans "metric rulez ok" Off!

[Eddylizard]

Originally Posted by Hans Off

What on gods earth is an "acre feet"?

That's the first time I have heard that unit of measurement!

Hans "metric rulez ok" Off!

The volume of water required to cover a one acre area to a depth of one foot.

http://en.wikipedia.org/wiki/Acre-feet

Approximately 0.124 hectare metres.

[ganzfeld]

Originally Posted by Hans Off

What on gods earth is an "acre feet"?

That's the first time I have heard that unit of measurement!

It's 43560 cubic feet of water. What's so hard to remember about that?

[Mosherette]

Originally Posted by Silas Sparkhammer

It isn't wholly nonsense: whenever a major dam is completed and water begins to fill the reservoir, seismographs will record a swarm of "microquakes," as the earth balances the changing stresses. My old geology prof. called this "isostasy."

I'd say isostasy isn't quite the right term for it. Isostasy is when the rigid lithosphere sinks or rises on the plastic asthenosphere according to the load its bearing - parts of Northern Europe (and I presume probably northern Asian and Americas too, I just never learned about them) are currently undergoing isostatic rebound after the relieving of the weight of the ice caps after the end of the last Ice Age. In my opinion, the forming of a reservoir by a dam would (a) be a negligible weight to have any effect on the isostasy of a continent and (b) the time it takes to have an effect is measured in hundreds if not thousands of years. I don't doubt that a microearthquake swarm could be caused by a reservoir filling up, but I think it's a localised effect and therefore not an isostatic response by the lithosphere.

However, you do have to watch out for this kind of thing with dams, reservoirs and heavy rainfall.

[Keeper of the Mad Bunnies]

Originally Posted by Silas Sparkhammer

It isn't wholly nonsense: whenever a major dam is completed and water begins to fill the reservoir, seismographs will record a swarm of "microquakes," as the earth balances the changing stresses. My old geology prof. called this "isostasy."

I have to agree that your professor was mistaken, as this is not really an example of isostasy, more likely it should be referred to as hydrostatic loading.

Originally Posted by Silas Sparkhammer

However, there is, to date, no link between this and any major earthquake.

I must disagree with you here. There are many examples of earthquakes caused by reservoirs. The largest I have seen reference to is Koyna, India in 1967 with a magnitude of 6.7.

Lake Oroville, M 5.7

Reservoir Induced Earthquake References

Originally Posted by Silas Sparkhammer

(A bit of math: the Glen Canyon Dam has a volume of 27,000,000 acre feet; this is the same volume as one inch of rainfall over a circular area 400 miles in radius. A major dam, however, takes weeks or months to fill, whereas an inch of rain can fall over a very wide area in as little as a single day.)

Yes, but rainfall doesn't hang around the same area for a sufficient amount of time.

However, while it is highly unlikely that torrential rainfall will cause an earthquake, I would not say it never could be the cause. It would definitely be a lower priority concern than the direct effect of flooding.

James Powell