Hi Beth. When you think of a fault try to see it in a 3 dimensional form. It has length, depth and width. It is almost never like the line you see on the map. That fault can be 10 miles long, 8 miles deep and 2 miles or more wide.

The fault can lock near the bottom, the top, in the middle, or it can lock from top to bottom. Something can trigger the first quake so there is just the slightest bit of movement which in turn sets up a sort of chain reaction at which time there can be many quakes at various depths. At times they will end with nothing more then a little popcorn quake or they are building towards the big one. The problem is that you never really know until one or the other happens, or doesn't happen.

My take on the recent quake activity in the LA area is the swarm was probably caused most by an external trigger and not by a large amount of stress buildup. The reason being is that there was an extreme wide area in which there was quake activity occurring about the same time. There was stress there, but not in sufficient amount to cause a quake of its own accord. It had to have had some help such as the most recent geomagnetic storm. Sort of like the straw that broke the camels back, but in this case it cause the straw to slide off the camels back before it became heavy enough to break the camels back. Take Care…Don in creepy town