When an earthquake occurs, two types of sound waves are generated and travel through the earth. the primary, or p, wave has a speed of about 8.0 km/s and the secondary, or s, wave has a speed of about 4.5 km/s. a seismograph, located some distance away, records the arrival of the p wave and then, 68.1 s later, records the arrival of the s wave. assuming that the waves travel in a straight line, how far (in terms of m) is the seismograph from the earthquake?