Magnitude is not an elevation measurement. The magnitude is a measure of energy released. Look again. This is showing two quakes with negative energy released! Both M -0.2 in Nevada.
I'm a faggot for this slide. I thought I found some USGS fuckery afoot. I will KMS now.
Here's the USGS explanation of why they have negative magnitude earthquakes:
How can an earthquake have a negative magnitude?
Magnitude calculations are based on a logarithmic scale, so a ten-fold drop in amplitude decreases the magnitude by 1.
If an amplitude of 20 millimetres as measured on a seismic signal corresponds to a magnitude 2 earthquake, then:
10 times less (2 millimetres) corresponds to a magnitude of 1;
100 times less (0.2 millimetres) corresponds to magnitude 0;
1000 times less (0.02 millimetres) corresponds to magnitude -1.
An earthquake of negative magnitude is a very small earthquake that is not felt by humans.
https://www.usgs.gov/faqs/how-can-earthquake-have-a-negative-magnitude?qt-news_science_products=0#qt-news_science_products