Some of the worst earthquakes in the country have happened in that area, or so I read somewhere I forget.
In all honesty, I am somewhat skeptical of the announced magnitudes (3.9 to 4.2) having that much widespread effect. I lived in Los Angeles for over 35 years, lived through two major quakes (Sylmar/1969, Northridge/1994) and scores (if not hundreds) of lesser quakes, and my experience was that 3.9/4.2 was only slightly perceptible. Perhaps enough to make you pause briefly in what you were doing, think to yourself, "Gee, that's an earthquake", and resume your activity. A quake that was felt over several states certainly seems like more than a 4.2.