Travel Time vs. Pressure (IMAGE) DOE/Lawrence Berkeley National Laboratory Caption Time delay of seismic waves was normally correlated with changes in stress due to barometric pressure (above). Two seismic events, one of magnitude 3 and another of magnitude 1, caused excursions from this relationship. The excursions were detected before the events occurred (arrows), possibly because of preseismic changes in the crack structure of the rock. Credit Niu et al Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.