I’ve read that, for instance, in Scandinavia the weight of glaciers has compressed the earth, and as the glaciers retreat, the earth is able to “rise” again.
So what I’m wondering is, if global warming is causing the ice caps to shrink and thus add a huge volume of water to the earth’s oceans, could all this added weight & pressure have an effect on deep sea earthquakes? Could it have caused an earthquake earlier than it should have occurred. Or, for all I know, could it have suppressed the quake so it wasn’t as powerful as it could have been, or delayed when it eventually occurred?
Further, if it could be scientifically proved that global warming did accelerate a deep sea earthquake that resulted in devastating tsunamis, could the governments of the affected areas sue the countries most responsible for acceleration of global warming?
What we are dealing with here is the increase in hydrostatic pressure caused by increased water depth. The volume of water released into the ocean is not so much what’s important, only the increased height of the water column.
The formula for hydrostatic pressure in psi (sorry, oilfield units as that’s the industry I work in) is:
.052 x fluid density (pound per gallon or ppg) x depth in feet
Sea water has a density of about 8.7-8.9 ppg. If we take the higher figure and assume a water depth of 6000 feet, the pressure at seabed is about 2776psi.
Fresh water has a density of about 8.35 ppg. If we assume, say, that the average water depth in given location may have risen three feet in the past fifty years due to global warming (and that’s a highly generous estimate) then pressure at sea bed for the example above has risen by just over 1 psi, or about 0.00036% . I have to doubt this would have any detectable effect on earthquake frequency.
Maybe there is an effect where a long column of ice has been reduced in height, but that would directly affect the area underneath the ice column, not elsewhere.
Inasmuch as the Sumatra quake that spawned the tsunami occurred over 18 miles below the earth’s surface, the weight of the column of water above the miles of solid rock would seem trivial to the forces acting on the tectonic plate.
There might actually be something to this, but it is a stretch.
It is thought that the re-activiation of the New Madrid Fault Zone during the Holocene (the fault zone itself is Precambrian) may be due to the “unloading” of sediment in the present-day Mississippi River valey. The Mississippi River hasn’t always existed, as you are undoubtledly aware, and hasn’t always been where it is today. Recent sedimentological, structural, and geophysical research has demonstrated that it may be possible that the release of overburden on the ancient, buried faults by the Mississippi River washing this overburden into the Gulf of Mexico could be responsible for the release of energy “stored” in this system.
Could an analogy be drawn with glacial overburden and global warming in places like Antarctica? Possibly. Could it affect faults deep underwater, such as the one off the coast of Sumatra? I doubt it.
Cites:
Van Arsdale, R., Waldron, B., Ramsey, N., Parrish, S., and Yates, R., 2003, Impact of river channelization on seismic risk: Shelby County, Tennessee. Natural Hazards Review, v. 4, p. 2-11.
Van Arsdale, R. B., 2003, The New Madrid seismic zone, p. 169-186 in Field Trip Guidebook for the 52nd annual meeting of the Southeast and South Central sections of the Geological Society of America: Tennessee Division of Geology, Report of Investigations 51.
We might see the opposite, that the tsunami will affect climate and ocean currents. The huge muddy ocean areas surrounding the stricken beaches will gather more solar heat, which will temporarily affect water temperature and currents. Such an effect will not last more than a few months, but ocean currents are the cause of the El Nino and La Nina weather patterns. (I just spent 5 minutes trying to find out how to make an n with a tilde. No luck. Sorry.)
The world’s increasing sea levels would seem to have had little to no chance of causing or strengthening the quake, but they may have had a hand in making the tsunami more devastating. After all, if the water is higher today than it was a few decades ago, it would take less of an event to trigger the kind of flooding we have seen than it would have taken a few decades ago.
If Michael Crichten is a doper, I’m sure he’ll be along to dispute this.
I’m not Crichton, but sea-level records indicate a possible sea-level increase of about 1-2 cm over the last century. True, this might be more serious in the future if global warming pans out, but it certainly didn’t affect the devastation caused by this wave. Also, it’s not at all clear that this rise is related to global warming. Look here: http://www.agu.org/revgeophys/dougla01/node3.html