Sky Quakes, Broken Gear, or Something Else.

[guyfriday]

Now that I have a little more time, I decided to look for more "air quakes", and I found these:

1 - M 1.2 - 16 km WNW of Emery, Utah. Location 38.997°N 111.408°W. Depth -1.3 km
Altitude on Google Earth: 2746 metres, so that earthquake was 2746 - 1300 = 1446 metres below surface.

2 - M 2.1 - 14 km S of Fern Forest, Hawaii. Location 19.337°N 155.143°W. Depth -0.5 km
Altitude on Google Earth: 716 metres. 716 - 500 = 216 metres below surface.

3 - M -0.8 - 63 km ENE of Pedro Bay, Alaska. Location 60.013°N 153.070°W. Depth -0.9 km
Altitude on Google Earth: 2026 metres. 2026 - 900 = 1126 metres below surface.

4 - M -0.5 - 7 km E of Mammoth Lakes, CA. Location 37.650°N 118.897°W. Depth -2.4 km
Altitude on Google Earth: 2340 metres. 2340 - 2400 = -60 metres.
This was the only one that, apparently, was above ground, but the depth uncertainty is 700 metres, so it's inside the error margin.

This is a reasonable, with the exception of Mammoth Lake, explanation for most of these negative altitude quakes.