Rechecking the USGS earthquake map of the Nevada-California border, one can notice that there are yet more four point mag plus earthquakes, as well as quite a few three point mag quakes. These events range from .9 km below the surface to 9 km down. These quakes are in an area where there is a surface old lava flow, one that you can clearly see on Google Earth. There is also an open strip mine very near where these quakes are centered. Another thing of note is that these quakes are taking place in the same spot, very localized, each within a few miles of one another. The USGS has not provided any wave forms for these quakes, but I suspect that this has something to do with the movement of magma or hot steam. If this is not the case, then they are manmade. Like I say a lot, the only way to really know the nature of these quakes is to examine the waveform to see if the waves are seismic or volcanic in nature, and then take a measurement of possible gases in the area, and if they have changed.
Here's the link to the earthquake list, where, as of this writing, is about 52 earthquakes in one tightly located area.
Here is that list at this very moment: