SAUSALITO , Calif. -- A geothermal project getting under way in the North Bay has people there concerned about a possible increase in earthquakes in an area known for quake activity.

East of Santa Rosa, the Geysers is the largest producer of geothermal energy in the nation. Seismologists say dozens of small but daily earthquakes have been a consequence of the process for 40 years.

Now some residents are worried a new deep-earth drilling project may increase the number of earthquakes.

For the upcoming geothermal project, Sausalito-based start-up Alta Rock Energy will be using a technology similar to one that set off a 3.4 magnitude quake in Basel, Switzerland three years ago. That quake damaged buildings and ended the project.

Company officials said their technique now is different and less likely to cause damage. That has not calmed the community's unease.

Douglass and Susan Bartlett own a cottage near Anderson Springs, a community two miles from the Geysers.

"They're like nothing we experience in San Francisco," said Douglass Barlett. "It's like a MacK truck hitting the side of your house."

The Bartletts worry about Alta Rock Energy's two-part plan that started Saturday. The first part of the project calls for drilling 2.5 miles into the earth. Then the rock layer above the magma will be cracked before water is added to generate geothermal energy. That part of the process still requires a state permit.

Local residents are wondering not only what will happen when the rock cracks, but also what will happen to the soil and the water sources.

At Alta Rock's offices, the mood was optimistic Wednesday evening. "We feel highly confident that we can conduct this project safely," said Alta Rock's Vice President of Operations James Turner.

The company's has substantial resources with backing from Google and investment firm Kleiner Perkins.

Company officials said they have left little to chance. "We don't anticipate an increase in seismic activity over and above what they see today. Hopefully we'll have a successful experiment and be able to provide a new way," said Turner.

The Bartletts say they support the creation of alternative energy sources, but the uncertainties loom large. "My biggest concern is they don't know what's going to happen. They really don't," said Susan Bartlett.

U.S. Geological Survey seimologist David Oppenheimer said it's impossible to predict what might happen when deep rock layers are disturbed. But given that the area is far from major fault lines, a major earthquake remains highly unlikely.