Hi All. Kind of looks like the M>4.0 quake northwest of Healdsburg has gotten the attention of some seismologists.

This was the second Sonoma County earthquake in two months and provides more evidence of the region's young and active fault system.

Both the 4.0 temblor five miles northwest of Healdsburg on Tuesday and a 4.3 earthquake centered in Santa Rosa on May 25 hit on the Healdsburg Fault.

There was, however, a notable difference between the two, with the first quake packing a much more powerful punch.

"This one looks like it's right on the extension where we've got the fault mapped right through Healdsburg," said Robert McLaughlin, a U.S. Geological Survey field geologist. "It seems we are getting some more activity on that fault.

Tuesday's quake was strong enough to get people out of bed, and was felt across Sonoma and parts of Napa counties though there were no reports of serious damage or injuries.

Geologists said the epicenter of the 07/29/2003 quake was in an area featuring harder rocks that make up the hills, but May's earthquake was centered closer to homes built over thick layers of softer, sediment-filled basins that tend to shake more.

The two earthquakes add to a string of moderate events over the past several years on or near three earthquake faults connecting the North Coast to the Hayward Fault system to the south.

"So if you look at all the activity, it's kind of like connecting the dots," McLaughlin said. "It gives us some idea of how some of these faults interact with each other."

I recently had the chance to talk to a seismologist about the worst-case quake that could occur in the Bay Area. It didn’t take him very long to come up with the combination of the Healdsburg, Rodgers Creek and Hayward faults rupturing at the same time. The earthquake wouldn’t be that much larger, but the damage would be in the neighborhood of 3 to 4 times greater then it would be if just one fault ruptured. I asked him what the odds were of that occurring. I never got an answer, but I did get the impression that while possible the probability wasn’t that great. Take Care…Don in creepy town