how far away could an earthquake be felt if san andreas fault ruptured

Short answer: A major rupture of the San Andreas Fault (magnitude ~7.8–8.0 in many scenarios) could be felt across much of California and into neighboring states — from Southern California up through the Bay Area and potentially felt as far away as central Nevada, southern Oregon, and northern Baja California depending on magnitude, depth, and local ground conditions.

Why distance varies

• Earthquake magnitude controls how much energy is released; larger events send perceptible shaking much farther from the rupture.

• Soil and sediment amplify shaking, so places built on thick young sediments (river valleys, basins) feel stronger shaking at greater distances than areas on bedrock.

• The length of the rupture matters: a long rupture (hundreds of km) concentrates energy and can produce strong shaking over a very large region.

Examples from historic and modeled events

• 1906 northern San Andreas rupture (M~7.8–7.9) was felt from southern Oregon to south of Los Angeles and inland into central Nevada — an area of roughly 200,000 square miles.

• The Southern California “ShakeOut” scenario (M~7.8, ~186 miles rupture) predicts damaging shaking across large parts of the Los Angeles Basin and perceptible shaking across many Southern California counties and beyond.

Practical ranges to expect (rule-of-thumb)

• Very strong / damaging shaking: within tens of kilometers of the ruptured fault trace (depends on magnitude and local site conditions).

• Noticeable shaking (people indoors feel swaying): for a magnitude ~7.8 event, commonly up to a few hundred kilometers from the rupture, depending on direction and geology.

• Rare, weakly felt motion or triggered distant quakes: seismic triggering and aftershocks have been observed hundreds of kilometers away in some cases, so the probability of some distant effects can extend to several hundred kilometers (or ~600+ miles for triggered activity in exceptional cases).

What increases felt distance

• Larger magnitude and longer rupture length, shallow depth, and propagation direction toward a population or basin increase felt distance.

• Basin amplification (e.g., Los Angeles Basin) and liquefaction-prone sediments increase local intensity even at greater distances from the rupture.

One short example story

Imagine a southern San Andreas rupture (ShakeOut-style M7.8) beginning near the Salton Sea: people near the fault would experience very strong, long shaking for tens of seconds; residents across greater Los Angeles and adjacent valleys would feel damaging shaking; people in the Bay Area, central California, and parts of Nevada could still feel the event as noticeable shaking hours earlier or as strong secondary shaking from triggered quakes.

Bottom note: Information gathered from public forums or data available on the internet and portrayed here.