In November of 2014, there has been a swarm of earthquakes in the Sheldon National Antelope Refuge in Northern Nevada, near the Oregon border.
To me, these quakes sound more like rock collapses than common earthquakes. Common earthquakes almost always sound like explosions because their energy is released all-at-once. Their audio envelope has a very steep attack, followed by an exponential decay. But these events sound like scratches, not explosions. Their audio envelope has a gradual attack! The attack part of their audio envelope was not instantaneous, but instead takes a few seconds to rise.
Something is slowing down the energy release. I imagine the sound rises slowly because it is due to rocks rolling down a slope.
Perhaps a sinkhole is growing. I wonder if it could be due to an unusually low water table, but I haven’t done any research into local rainfall.
Here is the seismogram of UW.JORV..EHZ of November 8th. Click on 2014.3188.8.131.52.910.UW.JORV..EHZ to hear these quakes, or rockslides, starting at 18:50 UTC. Every 30 seconds of audio represents 1 hour of activity.