There are three major factors: magnitude, your distance from the fault, and local soil conditions.
- Magnitude is discussed above.
- As for distance, the seismic waves that cause the shaking become less intense farther from the fault.
- Certain soil conditions amplify the shaking; generally, the looser the soil, the greater the amplification.
Although most of San Francisco escaped serious damage in Loma Prieta, those with unconsolidated landfill or soft soils (such as the Marina District) suffered serious damage. The ground motion in such areas was 10 times stronger than at neighboring sites on rock.
[Information from: "Frequently Asked Earthquake Questions" - "Earthquakes - A Whole Lotta Shakin’ Goin’ On" - State of California - Department of Conservation]