New findings on the developments of the earthquake disaster

[orogenicman]

Did the quake cause any downward displacement and permanent drowning of the coastal region behind the headwall like there was on the coast of Oregon as a result of the 1700 Cascadia quake? Since the Cascadia trench appears to be substantially closer to coast then the one off Japan, a rupture on the Cascadia trench will give much shorter warning time between quake and Tsunami. Is there any study on what sort of Tsunami would result from shelf and coastal topography off Oregon?

It is probably too early to tell. Likely, all that will come out once the quake is studied in detail and the results published. Kerry Sieh, of Caltech, published a paper in January of 2004 that warned of an impending earthquake along the Sumatran trench in the vicinity where the Boxer day earthquake occurred. His evidence included pre-quake uplift along the coast resulting in exposure of coral reefs and the islands offshore that was a result of flexure/bulging of the plate boundary prior to rupture. I don't know if any of that was seen before this Japanese event, but since that megathrust zone is further offshore, it is unlikely that such uplift was seen onshore. If it had, it would likely have raised alarm bells in Japanese academia. I guess we'll have to wait until some papers are published before we will know for sure.

As for the Cascadia subduction zone, I've known about it for a long time (ever since Brian Atwood first published his paper), but I am no expert on that area. I would do a search for some of his papers and see what he thinks. He's with the U.S.G.S. I do know that there have been tsunami studies of the Cascadia subduction zone, though I couldn't quote from any of them since I've not read them. What I do know is that any megathrust temblor of similar magnitude in the Cascadia zone would be devastating to the Pacific Northwest, and possibly further afield.

It is an interesting question whether such bulging would occur in the Cascadia, since the fault is of shallow dip. But having such a shallow dip angle also means that a much broader region could be affected by the quake itself. This does not bode well for Seattle and vicinity.

[Anomalocaris]

There is evidence of cyclic bulging associated with each of the past big quakes on Cascadia. There is evidence, for example, of land that was dry and forested when each cascadia earthquake struck, but were covered with tsnami sand deposite and then become innudated for hundred of years afterwards by brackish water after each quake, thus implying slow uplift between quakes, rapid subsidence during and after each quake. I don't know what is the degree of bulging now, but I do know there are formerly forested land that submerged with the 1700 quake that still remain submerged as coastal lagoons, with dead aspens sticking up through the water surface. So maybe the bulging has not reached its full extent and a quake is not imminent.

[orogenicman]

There is evidence of cyclic bulging associated with each of the past big quakes on Cascadia. There is evidence, for example, of land that was dry and forested when each cascadia earthquake struck, but were covered with tsnami sand deposite and then become innudated for hundred of years afterwards by brackish water after each quake, thus implying slow uplift between quakes, rapid subsidence during and after each quake. I don't know what is the degree of bulging now, but I do know there are formerly forested land that submerged with the 1700 quake that still remain submerged as coastal lagoons, with dead aspens sticking up through the water surface. So maybe the bulging has not reached its full extent and a quake is not imminent.

That sounds like what I have read. Understand that when oceanic crust gets subducted, what happens is that where the fault becomes locked on both sides, bulging can occur on the hanging wall side (in this instance, on the North American plate side). When the rupture occurs, the oceanic crust slides down into the Earth, releasing the built up stress, and so the bulge will subside. In the case of the Cascadia subduction zone, what I have read is that they have noted long-term slow slipping along the fault, an effect called a slow earthquake. This often happens when the rock on both sides of the fault consist of serpentine, which is very slippery and allows the rocks to slide slowly past one another. This might explain why there appears to be no apparent bulging going on today. And if that is the case, it could mean that the stress is slowly being released, and so not building up to a megaquake. But I don't think that this is in any way a certain thing.