>> reporter: scientists are asking park rangers to keep an eye on hot springs, sulfur pools and steam vents because of continuing seismic shocks. >> they can destabilize them. busy weekend. a lot of visitors. >> reporter: for about three years beginning in 1914, lasson erupted explosively. ash clouds. since last night's quake, no unusual volcanic activity. >> we have alarms. if we start to see increased levels. >> reporter: a line of faults runs from lake tahoe to lake almanor where the quakes are centered, then on to lasson. scientists still haven't identified the exact fault. they're swamped with so many aftershocks. >> it'll take us a few days to come up with a better image of what fault it's on. >> reporter: it's possible maybe even likely the quakes are not on any named fault. the area is riddled with faults, many of them unknown. reporting live, health and science editor, john fowler, ktvu channel 2 news.