joining us now to talk more about the strength of the earthquake is seismologist gene hartivic. thanks for joining us. rang thk this in terms of its magnitude. >> it's 6.0. so this means it's a this is a fairly large earthquake but not as large as the low ma pree ya ta earthquake in 1989. that earthquake had about 30 times more energy. >> i read that this is a fairly shallow quake. what is the significance of that? >> it was about 6 miles deep, which is fairly typical of this region, actually. one of the effects of the depth is that it was felt most strongly in sort of a small area around napa. and then it was felt through a broader area of california, but not with as strong a shaking. >> many victims have describe add waving feeling. does that say anything to you about what might have caused this or what it means? >> typically a larger earthquake like this will tend to have a long rolling motion like waves on a sea where as the smaller earthquake will have a short, jolting shocking moment to it. but the larger earthquakes can produce these big rolling motions. >> i see. tell me