Deep Earthquakes of Yosemite

Seismograms courtesy of University of Arizona

There are no recent earthquake faults at the surface in Yosemite. Yet there are some earthquakes, mostly under the Clark Range to the southeast of Happy Isles. They are unusual in two ways.

There are normal types of earthquakes, like the one whose seismogram is at the top at left. The shaking is quite rapid and the two kinds of waves (P and S waves) are easily seen (P at 97s, S at 105s). These are caused by rock breaking and sliding across a fault. Unlike most of California and Nevada, these earthquakes are quite deep, down to more than 30 km (18 miles) below sea level.

The other earthquakes are more unusual. They shake more slowly and the S wave in particular is hard to see, as in the bottom seismogram. These are even deeper than the others, being more than 40 km (25 miles) deep. Earthquakes like these are usually found under volcanoes. Does this mean there is magma moving under Yosemite? Scientists do not know, but there are no recent volcanoes in the park.

Yet.