I just read that the epicenter of the 06 shake was near the Mendocino Humboldt line
Another way of classifying an earthquake is by the seismic energy released. Frankly, I am not familiar with that method. When I first worked out magnitudes, they were done by hand by estimating the length of rupture, measuring the highest amplitude on the seismograph, measuring the duration of the shaking, etc. It's all done instantly today by computer algorithms, and the more reporting stations the better.
I would again caution against using tsunami evidence to back-calculate the size of the earthquake (if any) that spawned a particular tsunami. One of the largest tsunamis for which evidence exists (tsunmai deposits at unusual elevations along the coast of South America) have been related by some credible researchers to the sloughing off of the east half of the island of Maui. Such an event of mass wasting would be comparable to a wave caused by a very fat man doing a cannonball into a kiddie pool. ;^)
I'll have to round up my atlas or go out to the car to get a state map. What's the reference?
The evidence for the San Andreas fault tacre at Point Delgada dates back to an observation by Lawson (1908) of a lanslide in the area. I believe that Lawson mistook arecetn landslide, possibly caused by shaking from the earthquake, with the trace of the fault itself.
Mapping of the offshore extension of the San Andreas fault, northwest of Point Arena, conclusively shows that the modern trace of the fault extends northwest, consistent with the strike of the fault, as it passes San Francisco trending north-northwest through Bolinas, Tomales Bay, Bodega Bay, and then lastly onshore at Point Arena. The large curved trace, often drawn to connect the Point Arena area trace with the doubtful Point Delgada (Shelter Cove) landslide, and then with the onshore extension of the Mendocine Fracture Zone, is fanciful at best.
The relationship with the northern trace of the San Andreas fault, as a plate boundary, to the Mendocino fracture is highly complex, and most likely includes a some sort of deep, basal decollemont.
As far as the epicenter is concerned, I don't know if it can ever be located accurately. The earliest locations were based on greatest surface offset, near the Bolinas-Tomales Bay area (lateral offset of over 20 feet). Later work, and the study of subsequent earthqukes suggested that the epicenter may have been further south, near Daly City (some researchers even suggest the mid-1950's Daly City quake was an aftershock(!) of the 1906 event). There is no reason why the epicentral point must be near the greatest offset, or even near a central point of the earthquake trace (indeed, the 1857 San Andreas earthquke had an epicenter very near the northern terminus). However, the epicenter is usually the greatest offset.
An interesting idea was tested in the late 1960's, of comparing "stopped watch" and "stopped clock" data. The thining was that the earthquake could be timed by recording all of the data from timepieces that were detroyed during the 1906 earthquake. A distribution of the readings could be developed and estimates made of when the shaking occurred at any one point. The epicentral location would record the "first" shaking (always). The problem with this approach was that in 1906, the "time of day" varied from twon to town - that is to say there was no good, established datum. And the earthquake apparently shook for at least a couple of minutes, so the timing on the destruction of the watch had considerable uncertainty. I recall some results were published, but I do not remember if they were accepted as valid. I believe the results indicated an epicenter a little bit south of San Francisco - possibly the Daly City area.