ENAM: Seismic anisotropy of the Eastern North American Margin

Magnetic anomalies of the ENAM-CSE region with broadband OBS shown as circles and colored by depth. East Coast Magnetic Anomaly (ECMA); Blake Spur Magnetic Anomaly (BSMA); Inner Magnetic Quiet Zone (IMQZ); Outer Magnetic Quiet Zone (OMQZ).

The eastern north American margin (ENAM) formed during the early breakup of the supercontinent Pangaea ~200 Ma. Therefore, the structure of this passive margin holds the keys to understanding continental breakup. The ENAM Community Seismic Experiment (ENAM-CSE) consisted of an active source seismic experiment as well as a deployment of 28 broadband ocean bottom seismometers (OBS) from April 2014 – May 2015 that aim to answer these questions.

My research involves using ambient noise Rayleigh waves to image the relic flow patterns recorded in the lithosphere during continental breakup. We find azimuthal anisotropy with the fast direction parallel to the coastline, 90ยบ rotated from the paleo-spreading direction. This is at odds with the commonly accepted idea that the lithosphere records anisotropy parallel to the paleo-spreading direction. Our observations may be indicative of margin-parallel flow during the continental breakup. Alternatively, fast translation of the overall system relative to the slower breakup could have caused overprinting of the spreading signal by the plate motion signal.

Seismic anisotropy from the ENAM experiment. Fast directions are parallel to the margin rather than the paleo-spreading direction.