USGS has since upgraded the depth to a normal value but then a few hours after they did, there was another negative depth eq in the same spot and I am pretty sure they have changed the depth on that one by now, too.
what it seems is that these are being recorded as earthquakes but further research shows that other negative depth quakes nearby are recorded as quarry blasts. which makes more sense.
USGS has since upgraded the depth to a normal value but then a few hours after they did, there was another negative depth eq in the same spot and I am pretty sure they have changed the depth on that one by now, too.
what it seems is that these are being recorded as earthquakes but further research shows that other negative depth quakes nearby are recorded as quarry blasts. which makes more sense.