Found this article quite interesting....specifically the following comment..

Long Valley Caldera has shown sustained unrest since 1980 characterized by recurring earthquake swarms, inflation (dome-shaped uplift) of the resurgent dome, and increased levels of fumarolic activity accompanied by high concentrations of carbon dioxide (CO2) gas in the soils around Mammoth Mountain on the southwest margin of the caldera.

[link to www.icdp-online.org]

There has definitely been further uptick in activity of late so that means the volcano has been showing sustained increased actiivty for 32 years...makes you wonder exacty what has built up underneath in all that time...quakes are getting shallower so can now understand why they decided to do an indepth survey of the area to find out exactly what is going on.