Assuming you have latitude and longitude of the point from which you want to search:
DECLARE @Origin GEOGRAPHY,
-- distance defined in meters
@Distance INTEGER = 40000;
-- center point
SET @Origin = GEOGRAPHY::STGeomFromText('POINT(-122.084039 37.42227)', 4326);
-- return all rows from events in 40km radius
SELECT * FROM dbo.Events WHERE @Origin.STDistance(Localizaton) <= @Distance;