Monday, October 21, 2013

Shakin' It

The Clark Range, within the southeast corner of Yosemite National Park, has been seismically active in recent years. Many nearly imperceptible earthquakes occur here each year. There was a series of 4 shakers last night, some of which were noticed on the west side of Yosemite. The park community of El Portal sits astride the boundary of the granitic batholith and the older metamorphic belt. The way ores can concentrate near a contact like this, vibrations may, as well. Deep but slender barium mine excavations at the igneous/metamorphic boundary may serve as sound boxes where the resonances of the earth can surface.

When the Merced River is low, El Portal is a pretty quiet place, especially at night. Some of us heard at least some of the four 1.0-2.2 magnitude temblors as deep roars, lower pitched and shorter in duration than a passing jet. I noted the time of the clearest roar, at 2:54 a.m., and there it was on the USGS website, as a restless moment east of Gray Peak, and 15.9 km deep.

Aspen on the East Side and in small pockets within the park, are past their peak color, but still bright. In the Valley, the sugar maple has gone bare, but there's lots of color remaining.

Dogwoods are red,

The sky is blue.

The oaks are all golden,

And maples are, too.