Here it is Sept.24 and look what happened the last hours.
BIGGER ONES
Today: 6.9 magnitude earthquake near Levuka, Eastern, Fiji
Today: 6.4 magnitude earthquake near Neiafu, Vava‘u, Tonga
Today: 5.6 magnitude earthquake near Nereju Mic, Vrancea, Romania
Today: 6.3 magnitude earthquake near Tamisan, Davao, Philippines
Yesterday: 6.2 magnitude earthquake near Katsuura, Chiba, Japan
WOW!
Now, why don't these make the headlines instead of random events about animals etc.???
Not a bad question. Earthquakes have been getting to be more frequent in recent years, but then the public has become jaded with news of earthquakes so the news doesn't sell like random events about animals, etc. People never get tired of news about animals, etc., but maybe that's a GOOD thing.
The increase of earthquakes in middle America raises awareness for two reasons. A lot of people who had thought they were never going to go through the terror of an earthquake are finding themselves having to go through it anyway. Secondly, the building codes in areas where quakes are infrequent are not as stringent as codes in earthquake-prone areas. The National Building Code actually has earthquake zones drawn out in which less likely areas do not have to use as much reinforcing steel (for example) or shear wall specification is less demanding. Hold-down anchors are not used much and base plates on steel frame columns are thinner. In a word, the construction details allow for cheaper construction, and the buildings are more easily damaged by earthquakes.
After the Northridge quake in 1994, the code was revised to require UPLIFT resistance on base plates to the effect that tall buildings all over the county had to be retrofit with thicker base plates. It was the first quake in recorded history that registered a 1.5 G uplift, which means that one and one-half the weight of the building pulled UP on the framework, causing many of the base plates to CRACK under the stress. Imagine replacing the heavy 2" thick steel base plates welded onto all the columns of a high rise, each of which holds up 300 tons of weight. You have to jack up the column, cut the old plate off and replace it with one 4" thick, then weld it on with as many as 100 weld beads going all around the column, before you can let the column down again, then move on to the next column. One column at a time. Not to mention re-drilling all the anchor bolts and replacing them with thicker, longer, stronger ones, and more of them. Some of the bolts are two inches thick.
In Japan, they build their high-rise steel frame buildings on shock-absorbers and roller skates (so to speak) so that base plate fracture isn't going to happen.
A 26-story building in Los Angeles is today able to emerge unaffected by a 7-magnitude quake, whereas the same floor plan and elevation built in Tulsa, Oklahoma would likely be severely damaged, and the reason is, it isn't the same building. It might LOOK the same and have the same features, but the strength of the framework and seismic resistance is less, because the Building Code does not demand as much in Tulsa as it does in L.A., since it is in a seismic zone less prone to strong quakes. I doubt there has ever been a 7 mag quake in Tulsa, but we've had worse than that in L.A.
In the past few years there have been quakes in areas where no quakes are expected to occur, and new earthquake faults are being discovered as a result.
The way things are going, who knows what will come in the future?
Topic: Another EARTHQUAKE (Read 1410 times)