How large is a region of Low Pressure? If a map indicates that there is low pressure around New York, will Chicago be affected?

No I don't belive so

Explanation:

I don't think I pocket of pressure could possibly go half way across the United States

true. earthquakes are felt whenever there is a slip around a fault in the rocks below the earth. this reorientation of faults create sesmic waves and is known as earthquake, the severity of which is measured in richter scale. these are more prominent in hilly regions as the rocks usually form faults to balance the pressures on it.