August 24, 2011
And the Walls Came Tumbling Down
image by Кузьмин Владимир (Vladimir Kuzmin), Russia, Moscow
On Tuesday afternoon at 1:51 PM, millions of people in the eastern US and Canada were shaken by an unusually large earthquake. Nearly everyone in my building felt the magnitude 5.8 earthquake, but I didn't; how sad to miss such a gift from nature. One of the interesting features of this earthquake was the very wide area where it was felt. A similar size earthquake in California would have been felt in a much smaller region. Seismologists say that the crust in the western USA is strongly fragmented into many blocks so that the seismic waves aren't easily transmitted. But in the east the crust is ancient and strong, so that a quake in one area gets transmitted widely, with the crust ringing like a bell. As soon as a TV seismologist said that phrase I immediately thought of the Moon, which also has an ancient and strong crust that indeed continues to vibrate long after a moonquake, like a powerful peal from a bell. This implies that seismic shaking caused by impacts onto the lunar surface was more widely damaging than I had previously thought. Consider Vladimir's image. When first formed, every one of the larger craters here looked like Tycho. Each had a complex wreath of terraces stepping down from the rim crest to the floor. But they don't now. Their walls are smooth, having lost all vestiges of terracing. Part of the smoothing was due to covering by ejecta, but long-lasting shaking from every impact that occurred must have also caused downslope movement that reduced wall slopes and variations of topography. In fact, in looking at this image I realize that the attraction of this classic view is because Tycho is the only fresh feature superposed on a bed of its worn out predecessors.
STF8" Mirage Mak-Cass, Barlow 2x, DMK31 / UV-IR cat filter "Baader" / 30 fps, 1/60.
Processing in AviStack, postprocessing in AstraImage (deconvolution) and PS (curves, contrast, noisereduction).
Rükl plate 64
Yesterday's LPOD: Unknown Boundary
Tomorrow's LPOD: Classic Geology