1. Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089, USA
2. GNS Science–Lower Hutt, 1 Fairway Drive, Avalon, Lower Hutt 5011, New Zealand
3. Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, 595 Charles E Young Drive East, Los Angeles, California 90095, USA
4. Department of Geography, University of Sheffield, Western Bank, Sheffield S10 2TN, UK