Isabella Anomaly (image) Brown University Caption Mostly gone, not forgotten: the Isabella anomaly (IA), is the seismic signature of a "fossil" slab of the Farallon oceanic plate that was pushed under North American starting around 100 million years ago. The anomaly occurs at the same depth as known Farallon slabs under Washington and Oregon, and lines up due east of a known Farallon fragment off the coast. Credit Forsyth lab/Brown University Usage Restrictions None 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.